inclining experiment vessel

Cult of Sea

Maritime Knowledge base

The Inclining Experiment – Ascertain the GM of Vessel

Ship’s stability calculations not only rely on the ship’s geometry but also on the knowledge of where the ship’s centre of gravity (G) is positioned. Although the distance of G from the keel can be ascertained for various conditions that the ship may be in, it is essential that it is accurately known for one specified ship condition.

To this end, the need to carry out an inclining experiment becomes necessary and from this, two facts should become known:

the displacement; and
the position of G in a known ship’s condition.

The inclining test is carried out to find the lightship KG at the lightship displacement. It is sometimes known as a ‘ controlled list experiment ’. By conducting the experiment by means of a series of weight shifts, the GM of the vessel can be ascertained under the test condition. This GM value can then be compared with the ship’s KM to obtain the vessel’s KG value: KM – GM = KG

The environment of the dry dock is ideal for performing such a stability check. While the vessel is in the dock, it is usually in its light condition, the water is still and the facilities for moving known weights are readily on hand.

Conditions for Carrying Out the Inclining Experiment

The vessel should be upright.
The moorings should be slack, allowing the vessel to be inclined without restraint.
The vessel should be in still water conditions.
The density of the water should be known.
There should be no free surface action inside the ship’s tanks.
The contents and weights of all the ship’s compartments should be known.
Calm weather conditions should prevail.
The vessel should be clear of all unnecessary personnel.
The light condition displacement should be known from the builders.
The fore and aft draughts and the mean draught should be noted.

Experiment Preparations

The ship in an upright position, in its light condition, is fitted with a wire plumb line suspended from a high point on the transverse centre line. The ‘ plumb bob ’ on the end of the line is set into a horizontal trough of light oil or other viscous substance to dampen the movement of the plumb bob, once the vessel is inclined. Fastened to the edge of the trough is a graduated scale batten, measured in millimetres.

The inclining weights are then placed on board, preferably by the dockside cranes. These weights are usually fitted with a wheeled platform to assist movement on board the vessel, throughout the period of the experiment. Finally, all non-essential persons are sent ashore and the gangway is landed.

Conduct of the Experiment

The vessel is then caused to be listed over, by moving the weights of the ship’s centre line, to a measured, accurate distance in a horizontal direction.

Because the exact weight and the exact distance are known, a set of listing moments can be obtained.

List Moments + Displacement = GG1 (namely the horizontal shift in the ship’s C of G)

Unless the displacement value is known, it would be usual practice to carry out a draught survey prior to conducting the experiment in order to obtain the exact displacement figure.

Graphic Presentation (vessel floating freely)

Consider the two similar triangles ABC and GMG1
In triangle ABC: AB represents the length of the plumb line.
BC represents the deflection when the ship is heeled.
In triangle GMG1: GM represents the ship’s metacentric height in this condition.
GG1 is the shift of ‘G’ due to the moving weight.

As the triangles are similar: Then Tan Ø = GG1 + GM but Tan Ø = BC ÷ AB Therefore: GM = GG1 × AB + BC But GG1 = (w × d ) ÷ Displacement Therefore: GM = (w × d × AB) ÷ (Displ. × BC) Where: w × d = list moments (in tonne metres) AB = Length of the plumb line (in metres) BC = Deflection of plumb line (in metres) Displ. (W) = Ship’s weight in this condition

Inclining Test – Example

Question 1.:

A vessel is to undergo an inclining test in the following condition:

Displacement = 9,400 tonnes KM = 8.5 metres Ballast on board =680 tonnes at a KG of 2.8 metres (FSMs = 166 tm) Fuel on board =160 tonnes at a KG of 1.4 metres (FSMs = 200 tm) Freshwater on board =80 tonnes at a KG of 3.0 metres (tank full) The inclining weight on board = 60 tonnes at a KG of 9.0 metres. The plumb line has a length of 7.6 metres. The weight is shifted 6 metres horizontally and gave a deflection of 850 mm Calculate the lightship displacement?

GM = (w × d × Plumb line length) ÷ (displacement × deflction) GM = (60 × 6 7.6) ÷ ( 9400 × 0.85) GM = 2736 ÷ 7990 GM = 0.3424 m KG = 8.5 m – 0.3424 = 8.1576 m

Take moments about the keel:

Comm Weight x KG of Distance = Moment Displ 9400t x KG of 8.1576m = 76681 tm Ballast – 680 t x KG of 2.8m = – 1904 tm Fuel – 160 t x KG of 1.4m = – 224 tm F.W. – 80 t x KG of 3.0m = – 240 tm Incl Wt – 60 t x KG of 9.0m = – 540 tm FSMs – 360 tm 8420 t 73407 tm Lt. Ship KG = 73407 ÷ 8420 KG = 8.7182 metres

Hatch Covers - Function, Inspection, Tests,…
BLU Code - Code Of Practice For The Safe Loading And…
Cargo Calculations - Tanker Work
Ballast Water Management - Merchant Ships
Condition Assessment Scheme (CAS)
Gas Tanker - Types, Tanks, Reliquefaction &…

Panamax Container Ship Completes 1st Arctic Voyage & Reaches China In Just 3 Weeks

Study Finds One-Third Of Seafarers Forced To Pay Illegal Recruitment Fees

Inquiry Reveals OceanGate CEO Knew Titan Submersible Would Fail & Kill Him

Wallenius Wilhelmsen To Upsize 4 Vessels Into The Largest PCTCs Ever Built

Ship Stability: Intact Stability Criteria and Inclining Experiment

Remember, in the first article of this series , we had mentioned that the value of GM needs to be obtained at various stages from design to construction of a ship. We had also mentioned that the purpose to obtain the value of this parameter at different stages differs from stage to stage.

The first time when the metacentric height of a ship is estimated, is during its initial design stages using the following methods:

Empirical Formulae: A number of empirical formulae have been developed based on results of experiments made on different types of ship hull forms that help naval architects to approach to an expected value of metacentric height based on very basic dimensional parameters, like Length, breadth and Depth of the ship. Though the results obtained from these empirical formulae are not always accurate, they are used to arrive at an approximate value, which is very necessary, since ship design is a closed loop iterative process.
Initial Hydrostatic Calculations: Once the hull has been designed based on the results obtained from the empirical formulae, it is necessary to calculate the metacentric height using the values of other hydrostatics. The formula used in this stage is as shown below:

The purpose to calculate the GM at this stage of design is to compare it with the value obtained from empirical formulae, and decide on the requirement of iterations in the hull design. For conventional designs, the percentage difference between the two would be within 2 to 3 percent. However, in case of novel designs, the values obtained at this stage is solely reliable, not the ones obtained from empirical calculations.

This article will discuss about the other two stages of ship design and construction where evaluation of GM is an absolute necessity and plays a major role in ensuring that the ship is stable, and built as per the requirements of the client.

Stability Criteria:

A number of criteria that are based on the shape and nature of the stability curve of a ship , are used to evaluate the stability of a ship. Remember, that since we are discussing about intact stability , we will only focus on intact stability criteria, i.e. to evaluate the point where the ship becomes unstable, the values of certain parameters will be obtained from the stability curve pertaining to the least favorable loading condition.

Some of the features of the stability curve that are studied here are:

The steady heel angle in case of any heeling moment (wind moments, grain shift moments, etc.) This angle is shown in the following figure, at the point of intersection of the heeling curve and static stability curve. This angle plays a major role not only in determining the safety of crew, personnel, and cargo on board, but also helps in determining the angle at which the deck edge of the ship is likely to submerge. In other words, it helps us evaluate a ship’s resistance to capsizing, for a given loading condition.

The range of positive stability for each loading condition. It is important to know this parameter because it gives us the angle upto which the ship can heel before capsizing.
The magnitude of the heeling arm relative to the righting arm for every loading condition. The available difference between the righting and heeling arm gives us the allowable margin for further upsetting forces (wind, waves, etc.) before the ship attains negative stability.

Some of the criteria used to assess stability of a ship are also based on the dynamic stability of the ship. So, what is dynamic stability? Whatever we have discussed in the previous articles on stability, we have only dealt with Static Stability, i.e. stability of a ship when it is static. You could imagine it as if you have photographed a ship that is heeling, and studied its stability for that static condition in the photograph. However, dynamic stability deals with the study of stability over a range of angle of heels on the curve of intact stability.

For any given angle of heel, dynamic stability is the measure of the work done in heeling the ship to that angle, very slowly and while maintaining constant displacement. This is measured by the area under the static stability curve upto that angle, as shown in the figure below, where the grey shaded area is the dynamic stability of the ship at 30 degrees of heel.

So if at every angle of heel, the area under the static stability curve upto that angle is plotted, the curve for dynamic stability is obtained, which is shown in blue. This curve plots the amount of energy that the ship can absorb in order for it to heel upto a certain angle.

As per as dynamic stability criterion is concerned, we are more interested in evaluating the Residual Dynamic Stability of the ship in the following conditions:

Shift of cargo within the ship.
Presence of wind heeling moments.
Wave heeling actions.
Lifting of weight over one side.

All the four above cases result in a heeling moment which can be plotted similar to that in Figure 1. The area between the heeling moment curve and the righting moment curve (curve of static stability) is the Residual Dynamic Stability, and is less than the Dynamic Stability in absence of any of these upsetting forces. This value is evaluated for every loading condition and is tallied with a criteria set by governing bodies.

There are various international and national governing bodies that have established a set of criteria for ensuring adequacy in stability of ships. Some of these bodies are:

International Maritime Organization (IMO)
US Coast Guard (USCG)
American Bureau of Shipping (ABS)
Directorate of Naval Design (DND), Indian Navy

DND, India has set a series of stability criteria that are to be complied with, by all the ships serving for Indian Navy and Indian Coast Guard. Information regarding the same is classified, and hence, out of the scope of this article.

Our focus will be on the criteria set for merchant ships that ply on national and international waters . These criteria are laid down by International Maritime Organization (IMO) in The IMO Code of Intact Stability for Merchant Ships . This code specifies the formulae that are used to calculate:

Heeling arm due to winds and rolling.
Heeling arm due to grain shift or shift of dry cargo.
Heeling arm due to crowding of passengers on one side.
Heeling due to high speed turn.

The above four parameters are used to plot the heeling arm curves for each condition. The GM values are calculated by carrying out stability calculations at each loading condition considering reduction in metacentric height due to free surface effect. The results are all plotted on a stability curve. The values obtained from the curve should follow the following stability criteria for all merchant ships:

The area under the GZ curve must not be less than:
055 meter radian up to 30 degrees.
09 meter radian up to 40 degrees or the smallest angle of heel at which flooding takes place through openings (this angle is called the Downflooding Angle ).
03 meter radian between 30 to 40 degrees or the downflooding angle (whichever is the least).
Righting arm (GZ) must be greater than 0.20 meter at 30 degrees.
Maximum righting arm should occur at an angle more than 30 degrees.
Minimum metacentric height should be 0.15 meter.

The criteria mentioned above, are however, only a part of all the criteria mentioned in the code. If any criteria is not complied with, required changes are to be made in the loading conditions or tank capacities, or tank positions, depending on the criteria and which stage of design it is.

The Inclining Experiment:

An inclining experiment is carried out when the construction of the ship is completed up to a stage when all the components that contribute to the lightship weight have been installed. The primary purposes for carrying out an inclining experiment are:

To measure the lightship weight of the ship.
To find the vertical, longitudinal, and transverse positions of center of gravity.
To calculate the metacentric height of the lightship.

It is always conducted by the shipbuilder because, at this stage, the shipbuilder must prove to the client that the lightship weight has not exceeded the design value. This is a very important milestone for the shipbuilder because, often, marginal increase in weight is likely to be observed due to various manufacturing constraints. It is due to this reason, a weight margin of approximately 15 to 20 percent is allowed in the technical contact. However, if the difference between the design lightship weight and that calculated during the inclining experiment exceeds weight margin mentioned in the contract, the shipbuilder must pay a penalty for each extra ton.

The experiment is carried out by inclining the ship using known weights. The known weight is first shifted to one side of the ship, and the inclination is measured by means of under deck pendulums placed at various longitudinal positions along the center line of the ship. The bobs of the pendulums oscillate on battens with readings marked on them. The length of the pendulums are usually about 10 to 12 meters, and they are submerged in oil or a dense fluid so as to increase damping.

When the ship is ready for the experiment, the weight is shifted on the deck in a transverse direction. This causes the ship to list. The ship is first allowed to settle down in this position and the deflection on the battens are measured on all the pendulums. The mean deflection is then calculated and considered as the value to be used for calculations. The same process is repeated by shifting the weight to the opposite side. In some cases, multiple observations are taken using different weights.

The above figure shows an inclining experiment in which a known weight of ‘w’ tonnes has been shifted by a distance ‘d’. The deflection of the pendulum is read as ‘BC’ on the horizontal batten. As a result of shift of weight on the ship, the center of gravity of the lightship shifts from ‘G’ to ‘G 1 ’ .

The metacentric height can then be calculated using the following expressions:

Where, ‘W’ is the measured mass displacement of the ship; AB is the length of the pendulum used; BC is the mean deflection read on the batten.

There are a number of precautions required to be taken in order to attain fairly accurate results, and they are to be ensured by the shipbuilder before the experiment commences:

The experiment should be carried out when no beam winds are present. In case beam winds are unavoidable, corrections of metacentric height for beam winds are to be incorporated into the calculations.
The ship must be floating upright at zero heel angle, and must not be restrained by mooring ropes.
All lose weight present inside the ship should be restrained. Often, a lot of temporary structures like scaffoldings, wooden platforms, welding machines, etc. are present inside the ship during the experiment. They are either to be removed, or to be fixed to the ship so that they do not shift during the experiment. In the second case, their weights are to be recorded and the weight of the ship ‘W’ is to be corrected accordingly for calculations.
Tanks should either be emptied or pressed to full capacity. In case none of that is possible, the level of liquid in the tank should be such that free surface effect is minimum, and corresponding free surface corrections should be made in calculation of the metacentric height.
There are a number of personnel who are required to be on-board during the experiment. The number of personnel is to be kept to a minimum, and they are supposed to take pre-decided positions on the ship (which is usually along the centerline) before the readings are taken.
All interconnections between tanks should be closed, irrespective of whether the tanks are empty, fully pressed, or partially filled.
The draft marks of the ship must be read before the experiment begins, so as to ensure design trim and absence of a condition of loll.
The density, salinity and temperature of the water on which the ship is floating, must be measured and recorded before the experiment. This density must be used to calculate the mass displacement of the ship ‘W’ . It is always recommended that the experiment is carried out in sea water.

Though the stability characteristics of a ship can be determined with considerable precision, most authorities and shipbuilders find themselves in a trap while quoting the primary characteristics like metacentric height and righting lever with great accuracy. This is because, a design cannot be replicated to the fullest, in the real world. Hence, a naval architect must be aware of the following reasons that often cause the real-time values to vary from the design values:

Ships are not built exactly according to the lines plan, because the curvature of plates is almost always not achievable as per the lines plan. There is always a difference of 0.1 to 0.3 percent in the curvature, which when scaled up to the size of the ship, creates a shift from design values.
The weights and center of gravity vary within a margin, due to the contribution of plate thicknesses and added weight due to welded joints.
The accuracy of the actual KG of the ship as assessed, depends largely on the level of accuracy involved in the inclining experiment. It is based on the results of this experiment that the stability booklet of the ship is updated, and further stability parameters are calculated.
One of the most important assumptions in all the stability calculations are that the ship is floating in an even keel or zero trim condition. However when values are recorded in real life, they are done in design trim conditions, and not at even keel. This results in a visible difference between design and practical values. However, recent design software are capable of carrying out all stability analyses in required trim conditions, which shoots up the level of accuracy.

All that we have discussed till now is, the stability of a surface ship when it is intact. How is the stability of a ship affected when its hull is damaged? How is a ship designed to be safe even if one or two compartments are completely flooded? These are aspects that fall in the category of Damaged Stability of Surface Ships, which we will be our topic in the next article of this series.

Disclaimer : The information contained in this website is for general information purposes only. While we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the website or the information, products, services, or related graphics contained on the website for any purpose. Any reliance you place on such information is therefore strictly at your own risk.

In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever arising from loss of data or profits arising out of, or in connection with, the use of this website.

Do you have info to share with us ? Suggest a correction

About Author

Soumya is pursuing Naval Architecture and Ocean Engineering at IMU, Visakhapatnam, India. Passionate about marine design, he believes in the importance of sharing maritime technical knowhow among industry personnel and students. He is also the Co-Founder and Editor-in-Chief of Learn Ship Design- A Student Initiative.

Daily Maritime News, Straight To Your Inbox

Join over 60k+ people who read our daily newsletters

By subscribing, you agree to our Privacy Policy and may receive occasional deal communications; you can unsubscribe anytime.

BE THE FIRST TO COMMENT

How to calculate known weight ?

When G1G2 & LBP is not given, and we’re asked to find the GM of a vessel, do we use:

GM = (w × d × Original Length) ÷ (Displacement × Deflection); to find the answer?

Like say for example, a vessel with the displacement of 4950 t, which is initially upright when a weight of 25 t is moved across the deck 9.14m and at the same time a plumb line of 4.26m in length is deflected 0.3m. Find the GM.

GM = (w × d × Original Length) ÷ (Displacement × Deflection)

= (25t × 9.14m × 4.26m) ÷ (4950t × 0.3m)

= (973.41) ÷ (1485)

Therefore, GM = 0.655 m.

We didn’t really cover this topic well in class so I don’t know if I did the correct thing to find the answer (GM).

tan theta is BC/AB NOT AB/BC…

corrected Deepak. Thank you for keeping a sharp eye.

Your email address will not be published. Required fields are marked *

Subscribe to Marine Insight Daily Newsletter

" * " indicates required fields

Marine Engineering

Marine Engine Air Compressor Marine Boiler Oily Water Separator Marine Electrical Ship Generator Ship Stabilizer

Nautical Science

Mooring Bridge Watchkeeping Ship Manoeuvring Nautical Charts Anchoring Nautical Equipment Shipboard Guidelines

Explore

Free Maritime eBooks Premium Maritime eBooks Marine Safety Financial Planning Marine Careers Maritime Law Ship Dry Dock

Shipping News Maritime Reports Videos Maritime Piracy Offshore Safety Of Life At Sea (SOLAS) MARPOL

WAIT! Did You Download 13 FREE Maritime eBooks?

Sign-up and download instantly!

We respect your privacy and take protecting it very seriously. No spam!

World Maritime Day 30% OFF Sale!

Knowledge Of Sea

We will keep you updated

Inclining Experiment

Why the vessel has to be inclined .

To obtain the metacentric height it is necessary to determine the position of the centre of gravity `G’. This calculation consists of two parts.

a) The first is the finding of the height of the metacentre ‘M’ above the keel ‘K’. This is purely geometrical depending only on the form of the ship.

The second is the height of the centre of gravity above ‘K’ and this depends on the lightweight of the ship hull including disposition of machinery and equipment, water or ballast, if carried and allowances for free surfaces.

Why Inclining Experiment

Ship’s officers are primarily concerned with the value of GM in any particular condition. The naval architect on the other hand is concerned about the position of the centre of gravity in the light ship or light mass condition, since it is the basis for calculations of stability for different condition of loading.

To determine the position of the vertical centre of gravity an inclining experiment is carried out. The immediate purpose of the experiment is to determine the metacentric height. The ultimate purpose is to obtain the height of the centre of gravity for a definite condition of the ship – the Light Condition.

Process for Inclining the Ship

A small known mass is moved transversely on the deck through a known distance. The resultant angle of heel is measured either by means of two pendulums or by an instrument called a stabilograph, which records directly the movement of the ship in degrees. Where pendulums are used, they should be as long as possible supported by a fine wire with a heavy bob weight. The deflection of the pendulum is measured against a horizontal batten as shown in figure later.

In the experiment, a mass (w) is moved transversely across the deck through a known distance (d). As the mass w is moved across the deck, the centre of gravity of the ship moves from G to G₁ such that:

where Δ = displacement of ship.

At the same time, the ship will be inclined through some angle Ɵ and will be in a position of stable equilibrium.

The centre of buoyancy B originally under G will have moved to B₁ to be in the same vertical line as G₁. GG₁ is parallel to the movement of w and hence the angle G₁GM is a right angle and

GG₁ = GM tan Ɵ

w x d= Δ xGM tan Ɵ

or GM = (w x d) / Δ tan Ɵ

also tan Ɵ = GG ₁ I GM = deflection of pendulum I length of pendulum

During the experiment, it is necessary to make several shifts of mass from side to side, take readings at each shift from the plumb lines and then use mean values.

Precautions to be taken during Inclining experiment.

The principle underlying the inclining experiment is simple but the carrying out of the experiment requires careful attention to ensure a reliable result. Since all subsequent stability calculations are based upon the position of the centre of gravity determined by this experiment it is essential that all the factors, which affect its accuracy, be considered.

A calm day should be chosen.
It is desirable that the experiment be made when the ship is nearly, if not, completed.
A list should be made of loads to be added, items to be taken off and items on board that are to be shifted along with their vertical and longitudinal positions of centre of gravity.
The ship must be floating freely. All mooring wires should be slack and shore gangways removed.
All tanks should be empty or pressed full.
All workmen, other than those engaged in experiment, should be sent ashore. Those on board should remain as nearly as possible in a constant position while readings are being taken.
All loose items such as derricks, boats, etc. should be secured, in their sia going condition.
Chalk lines on the deck should define the position of the inclining masses.
At least two plumb lines should be used one forward and one aft. A white wood batten should be placed so that its edge is close to the swing of the pendulum. If each successive position of swing is marked and numbered it is possible to check all the figures at the end of the experiment. A heavy plumb bob at the end of the line is conducive to steadiness and it is usual to have the bob swinging in the container of water in order to damp the oscillations. The pendulum readings could be used as a check on a stabilograph.
The draughts must be carefully measured. The draught amidships should also be taken by measuring with a batten the distance from the Plimsoll mark on each side to the water level. The hog or sag of the vessel is thus determined, and also the initial list, if any. The density of the water in which the ship is floating should be determined by a hydrometer.

Beyond the metacentre – towards more reliable inclining experiment outcomes

by RINA | 25th July 2023 | Editors Choice , The Naval Architect - News

Figure 1. Mesh model of a proa (reproduced from (a) with permission) Smith et al (g) in 2015 proposed adoption of Dunworth’s “generalised method’ of inclining analysis.

By Rob Gehling, FRINA

As a naval architecture student, I was taught that the metacentre was applicable only at zero angle of heel, irrespective of its role in determining the initial slope of the righting lever curve. But it can be easily proven that the metacentre moves around at small angles of heel and may not be on the centreline even for wall-sided symmetrical vessels. Plots of the vertical and transverse position of the metacentre often show that the metacentre can move vertically and off the centreline.

The lightship characteristics measured by inclining experiment are a fundamental input to managing a ship’s intact and damage stability throughout its service life or until it is re-inclined. In the latter case, considering that stability may deteriorate during the life cycle, informed decisions based on accurate GM measurements could feed back into design and operation for better stability management or indeed better designs.

It is, therefore, timely to re-examine the traditional inclining experiment analysis methods, taking account of the technological developments and tools now available to naval architects compared with those when I first inclined a ship in the early 1970s. My experience back in the 70s and 80s in inclining and reviewing reports for merchant ships could be summarised by the lightship VCGs of bulk carriers and single hull tankers up to 150,000dwt having a range of up to 10% depth, with no particular reason for the variation. These vessels were inclined in as light draught as practicable and under very tight checks on the consistency of GM measurements resulting from each weight movement. While these ships were generally very stiff from an intact stability perspective, the accuracy of measuring the lightship VCG from the inclining experiment may have been marginal from the broader safety perspective. A specification under which these inclining experiments were conducted drew attention not only to minimising “items on” and “items off” to obtain the lightship but also in changing the waterline such as by immersion or emersion of chines.

The importance of an accurate VCG with regard to damage stability has increased in recent years through amendments to SOLAS and MARPOL.

The wall-sided assumption that underpins the traditional GM method of analysing outcomes of experiments can be disproven by calculating the location of the transverse and vertical centres of buoyancy and applying the BM = I/Vol formula as the vessel is inclined.

Current developments

We now have computer modelling and calculation tools available to us for accurately tracking hydrostatic characteristics and the KN value at all stages of inclining. Most hydrostatic packages are no longer limited to moulded lines but can take account of hull thickness to provide more accurate hydrostatics. We no longer have to use free surface moments to track the centres of gravity for liquids on-board as the vessel heels, as computer models can similarly track these.

Commencing with his paper ref. (a) to the Pacific 2013 International Maritime Conference, and an expansion of that paper (b) in 2014, Dunworth has advocated for almost a decade for a change in the analysis of outcomes of inclining experiments to be based on KN values rather than classical GM. This method, later referred to by Karolius and Vassalos (d) as the “generalised method”, was described by (a) to provide reliable results for a proa hull form as a demonstration of its satisfactory application to asymmetric forms, centre of gravity off-centreline and changes to underwater geometry during inclining such as immersion/emergence of multihulls. The relevant hull form is reproduced here as Figure 1. In his second paper (b), Dunworth used the hull section model (HSM) to explore a range of inclining experiment scenarios on a hard chine craft, a theme that was further extended, including experiments with inclining in air in his most recent paper (c) in November 2021.

Figure 2. Component uncertainty contribution in the vertical location of the centre of mass for various inclining experiment parameters for the five case study ships (reproduced from (h) with permission)

In 2016 Woodward et al (h) published an assessment of inclining experiment parameters for five case-study ships of different types. The relevant diagram is reproduced with permission as Figure 2 and shows that the areas of greatest uncertainty are with the measured heel angle (for a ropax and buoy tender) and draught (for ropax). The figure was also reproduced in (d) whose authors extended the work to consider alternative methods of determining lightship characteristics in the diagram reproduced as Figure 3 which indicates an order of magnitude inaccuracy in VCG from the classical method compared with the alternatives.

In my view the problem with accuracy of angle of inclination could be improved by paying increased attention to its measurement. Possible measures include using multiple pendula, U-tubes (while attractive in terms of a U-tube across the breadth of a ship may be equivalent to a very long pendulum my experience is that viscous effects may result in reduced heel angles compared with pendula), midship draught measurement after each weight movement particularly for multihulls and apps or other electronic devices.

Figure 3. Percentage error for VCG, 2 degrees maximum heel angle and 0 degrees initial heel angle (reproduced from (d) with permission)

Apart from demonstrating the above-mentioned point with regards to movement of the metacentre, (d) provides an analysis of the accuracy of the various available methods of determining lightship characteristics, showing that the traditional classical GM method is at least an order of magnitude less reliable than the generalised, polar, and graphical methods.

The papers referred to above, when taken together, conclusively demonstrate that the classical method of analysing the outcome of an inclining experiment “will generally result in an incorrect VCG” as stated in (c). In it Dunworth notes that IMO’s Intact Stability Code (IS Code) (e) specifies in paragraph 2.22 of its introduction that the VCG can be determined “by applying basic naval architecture principles” to the information from the inclining experiment. Further guidance might be expected from the IS Code’s Annex 1 (f) but this document is only written in general terms. So paragraph 2.22 is likely to be interpreted to refer to the classical (GM) method. But in light of the information provided in the referenced papers and the assumptions involved in the classical method, paragraph 2.22 should more correctly be taken (and amended) to refer to the generalised (KN) method as that method more correctly reflects “basic naval architecture principles”. Accordingly, in (c) Dunworth questions whether continued and unquestioning use of the classical GM method would be consistent with RINA’s Code of Professional Conduct requirements, which are specifically for each member to:

“so order his/her conduct as to uphold the dignity and reputation of his/her profession: and to safeguard the public interest in matters of safety and health and otherwise” .

The generalised method should therefore be used in place of the classical GM method and any legislated requirements requiring use of the classical GM method should be amended to permit use of the generalised method in the public interest.

Conclusions

Since the generalised method has been proven much more accurate on a wide variety of hull forms, I would expect that, as an extension of what has already been demonstrated on a proa and chined vessels, the method will be proven to produce good results on all types of hull forms, including for example trimarans with surface-skimming side hulls, where the immersed body varies markedly as the vessel heels.

On the other hand, I would also expect that the generalised method might not produce markedly better results on a large catamaran high-speed craft, where the GM value may be in excess of 100m, since the variability of the intersection point for the various KN lines applicable during the experiment is likely to be substantial compared with the vessel’s depth.

Based on the above summary of papers on this subject, there are compelling reasons for all naval architects and regulators to adopt the generalised method, particularly for vessels whose waterplane may change to any significant extent across the range of heel experienced during an inclining experiment. These reasons are:

Lack of reliance on the metacentre being falsely assumed to be a single stationary point through which the buoyancy is assumed to act during the experiment;
Lack of reliance on the centre of gravity being on the centreline;
Catering for asymmetric hull forms;
Avoiding the wall-sided assumption by catering for immersion/emersion of chines, side hulls and so on; and
Taking advantage of improved accuracy provided by the capabilities of modern naval architectural software packages.

Even in such cases where the wall-sided assumption remains valid, the generalised method should be treated as at least equivalent to the classical method.

This article has been developed from that published in the April 2022 issue of The Naval Architect .

Finally, our profession should thank Richard Dunworth and Prof Dracos Vassalos for their perseverance in bringing this important practical subject to attention. The significance of references (a) and (c) has been recognised through Walter Atkinson Award for 2014 and 2022 being presented to Richard Dunworth for the best written paper published by or presented under the Australian Division of the Royal Institution of Naval Architects in the 12 months to 30 June of those years.

(a) Dunworth RJ, Back Against the Wall , Pacific 2013 International Maritime Conference, Sydney, and reproduced in The Australian Naval Architect , February 2014, pp30-35

(b) Dunworth RJ, Beyond the Wall , 12th International Conference on the Stability of Ships and Ocean Vehicles, Glasgow, June 2015

(c) Dunworth RJ, Scaling the Wall; Inclining Experiment Analysis on Vessels with Chines, Hull Discontinuities or Asymmetry , The Australian Naval Architect , Sydney, Australia, November 2021

(d) Karolius K B & Vassalos D, Tearing down the wall – The inclining experiment , Ocean Engineering no.148, Jan 2018

(e) International Maritime Organization: International Code on Intact Stability 2008, IMO Res. MSC.267(85)

(f) ibid, Annex 1 – Detailed Guidance for the Conduct of an Inclining Test

(h) Smith AC, Dunworth RJ & Helmore PJ, Towards the Implementation of a Generalised Inclining Method or the Determination of the Centre of Gravity , Pacific 2015 International Maritime Conference, Sydney, Australia

(i) Woodward MD, van Rijsbergen M, Hutchinson KW & Scott A, Uncertainty analysis procedure for the ship inclining experiment , Ocean Engineering 114 (2016), pp79-86

About the Author – Rob Gehling

On graduation in naval architecture in 1973 from the University of New South Wales, Sydney, Rob commenced his career as a design engineer at the Whyalla Shipbuilding and Engineering Works, builders of Australia’s largest commercial ships. In addition to design work, he undertook all types of naval architectural calculation work on ships under construction, including the conduct of inclining experiments and preparation of stability data.

With the shipyard closing in 1978 he joined the Department of Shipping and Transport in Melbourne, his main task being scrutiny of inclining experiment reports and stability data presented for regulatory approval. The organisation changed its name several times and moved to Canberra in 1982, becoming the Australian Maritime Safety Authority. Rob’s role also changed to move into ship design and construction regulatory matters as Chief Naval Architect and Manager Survey Planning & Development. He became Australian delegate to the International Maritime Organization’s Sub-committees on Ship Design & Equipment (DE) and Stability Load Lines & on Fishing Vessel Safety (SLF). He headed the working and drafting groups that drafted the International Code of Safety for High-Speed Craft in 1992-94 and was involved in its further development through to 2008. Rob chaired the SLF Sub-committee from 2005 to 2010.

A member of RINA’s Safety Committee since 1998, member of Council, past President and currently Secretary of the Australian Division, Rob has prepared this article on inclining experiments in furthering the Safety Committee’s efforts to improve maritime safety.

Harnessing wind power for the next generation of sustainable shipping

Commercial Shipping , Equipment , The Naval Architect - News

By Mikko Nikkanen, head of maritime, weather and environment, Vaisala With annual international shipping CO₂ emissions doubling since 1990 and now accounting for roughly 10% of global transportation emissions, the maritime shipping sector sits at a crossroads...

LR OneOcean expands digital portfolio with Ocean Technologies Group acquisition

Commercial Shipping , Rules & Regulations , The Naval Architect - News

Class society Lloyd’s Register (LR) has announced an agreement to acquire maritime e-learning software provider Ocean technologies Group (OTG) from private equity firm Oakley Capital. The buyout means that OTG, which provides critical training, compliance,...

Wind Propulsion 2024: Advancements in sails

RINA News , The Naval Architect - News

By Alberto Llopis Pascual, head of aerodynamics, bound4blue Since the decline of commercial sail-powered vessels, there has been remarkable progress in sail technology, driven by a renewed interest in sustainable maritime solutions. The modern sail has evolved far...

Sponsored: PALFINGER MARINE’s PFM 2100: A New Era of Heavy-Duty Cranes

Concept of the metacentre

Indexes of metacentric stability, vertical position of metacentre, vertical position of centre of gravity, inclining experiment, stability of submarines.

General arrangement features by ship type
Cargo handling
Watertight closures
Ballast tanks
Computing friction resistance
Wave-making resistance
Separation resistance
Resistance of submarines
Resistance in shallow and restricted waters
Ship form for minimum resistance
Action of propulsion devices
Interactions between propeller and ship
Efficiency of propulsion
General design and positioning of propellers
Model experiments
Dynamic stability of route
Steering and turning
Stopping and reversing
Rudders and planes
Heel when turning
Effect of propulsion-device action on maneuverability
Maneuverability of submarines in the vertical plane
Maneuvering predictions and model experiments
Ship motions in waves
Effect of shape and proportions
Hydrostatic and hydrodynamic loads in service
Variation of buoyancy and weight along the length of the ship
Determination of forces and moments
Superposition of calm-water and dynamic wave loads
Strength and stiffness
Structural configurations
Scantlings and strength calculations
Structural design of submarine pressure hulls
Detrimental effects of discontinuities
Materials of construction
Jointing, connections, and attachments
Structural tests of ships and models
Subdivision and floodable length
Situation after damage
Preparation of requirements
Compromises necessary
Preliminary design stage
Contract design stage

Metacentric stability

Our editors will review what you’ve submitted and determine whether to revise the article.

Encyclopedia of Greater Philadelphia - Shipbuilding and Shipyards
In-Depth History of Shipbuilding in Recent Times
Table Of Contents

One would think, at first sight, that the average surface ship , with its weight concentrated above its point of support (considered as the centre of buoyancy ), would fall over like a top that has stopped spinning. If properly designed it does not do so, because as the ship is inclined transversely, say by a strong wind, the centre of buoyancy of the immersed portion of the hull shifts sideways, in the same direction as the inclination. This is because the volume of the wedge of emersion shifts to the low side. At the new inclined waterline, the centre of buoyancy moves to the low side as well. The total buoyancy force continues to act upward along the true vertical. Provided no weights shift as the ship inclines, the centre of gravity remains at G, in the keel-to-deck centreline. The buoyancy force acting upward and the weight force acting downward through G produce a righting moment which acts to return the ship to its upright position.

For small angles of inclination, say less than 10°, the verticals through the shifted centres of buoyancy intersect the ship centreline at or close to a point M, called the metacentre. The stability provided by the action described is therefore called metacentric stability. For the situation most often encountered in practice, it is transverse metacentric stability. For a similar situation in which the ship is inclined or trimmed in its fore-and-aft centre plane, it is longitudinal metacentric stability.

If the centre of gravity of the ship is too high, the righting moment for any inclination is negative; that is, it acts to incline the ship still further. The ship then has transverse metacentric instability. Whether it will capsize or not depends upon whether the revised position G is overtaken by the vertical through the revised B as the inclination increases. If so, the ship remains in that inclined position, with a righting moment that is practically zero.

The distance GM for positive stability, known as the metacentric height, is taken as one index of the degree of metacentric stability. The other is the range of stability, or the angle of inclination at which the metacentric height diminishes to zero. For example, when a ship is heeled transversely until the depressed deck edge goes underwater, the centre of buoyancy cannot move to the inclined side far enough to keep the metacentre well above the centre of gravity on the ship centre plane. At a critical inclination the metacentre lies at the centre of gravity and the righting moment disappears. For inclinations beyond this the metacentric height becomes negative, the righting moment becomes a capsizing moment and the ship rolls over.

A greater range of metacentric stability can be built into a ship by raising the uppermost watertight deck to a higher position above the calm-water plane of flotation. The ship can then heel to a greater angle before water comes over the lower deck edge. For a craft like a sailing yacht , with a deep, heavy, stabilizing keel, the deck edge can actually go underwater and the range of positive stability can extend to large angles, provided water is kept out of the hull as the water level climbs higher and higher over the inclined deck.

The desirable value of transverse GM varies with the type, size, and service of the ship, but within limits it is still subject to the experience and judgment of the naval architect. It averages from 0.04 to 0.06 of the beam but may be as high as 0.10 of the beam for combatant vessels subject to heavy damage. For fishing vessels it may have two values, one for the outgoing and one for the return or loaded part of the voyage. The range of positive transverse GM for a normal ship to run in the open sea is usually in excess of 40° and may run as high as 70° or more, provided the hull remains intact and the weights do not shift.

The height of the metacentre above the keel, or other selected point, depends upon the shape and size of the underwater body and of the at-rest waterline. The total height KM is the sum of the height KB of the centre of buoyancy above the keel and the height BM of the metacentre above the centre of buoyancy. The latter is known as the metacentric radius. The distance KB can be estimated by an approximate formula, it can be calculated by procedures applying to irregular volumes, or it can be determined by a mechanical integrator. The metacentric radius BM depends entirely on the geometry of the underwater hull and can be calculated from the formula, BM = I / V where I is the transverse moment of inertia of the waterline plane about the centreline axis, and V is the immersed volume of the hull. This relationship was first derived by Pierre Bouguer in the 18th century. For a given ship length and underwater volume, both I and BM are proportional to the cube of the beam, so that the latter is an important factor in transverse metacentric stability.

The vertical position of the centre of gravity is as important as that of the metacentre in determining metacentric stability and the behaviour of the ship at sea. For a cargo ship, or even for a warship , this position may change by many feet, depending upon the nature, amount, and vertical position of the loads, fuel, and stores. Ballast may be used to increase the total mass moving in a seaway or to place G in a more advantageous position. Ice accumulating on the upper works of fishing boats, trawlers, and other small craft may be so thick, so heavy, and so high above the normal centre of gravity, as well as so difficult to remove at sea, that G rises above M and the craft capsizes.

Fortunately, the naval architect is able to make a full-scale check of the predicted or calculated metacentric stability before the completed ship goes to sea. By shifting liquids or solid masses whose weights and offset positions are known accurately, the centre of gravity of the whole ship is shifted and the ship is heeled. This shift is sideways for a determination of transverse and lengthwise for a measurement of longitudinal. The angle of inclination of the ship for each such shift is measured accurately with special devices. Then the actual metacentric height is determined for that loading condition. The height of the centre of gravity above the keel is then calculated from the relation.

When a submarine is in surface condition, its metacentric stability situation is the same as that of any surface ship. When diving or submerging, its water-plane area diminishes progressively to a negligible amount. The transverse moment of inertia of this plane likewise diminishes and with it the value of BM . Moreover, as the main-ballast tanks are flooded and the pressure hull is taken under, buoyancy is transferred from a low to a high position, so B rises in relation to the hull. Since G remains in its original position, M drops to the vicinity of G. Indeed, for some moments during diving and surfacing, it may be below G, with a negative GM . The flooding, venting, and blowing of the main-ballast tanks, with separate port and starboard controls, enable the submarine crew to counteract any list that may develop during this brief transition period.

When the submarine is under the surface, the water-plane area is zero, as is BM . This means that the centre of buoyancy of the pressure-proof hull (B 1 ) and M coincide. In this condition B 1 is higher than G, so that the action of the buoyancy force and the weight force produces a stable situation, and the craft is said to have pendulum stability.

JavaScript seems to be disabled in your browser. For the best experience on our site, be sure to turn on Javascript in your browser.

Sign in to use Tracker.

To use Tracker, please sign in to your account.

Not registered? Create an Account

Standard Guide for Conducting a Stability Test (Lightweight Survey and Inclining Experiment) to Determine the Light Ship Displacement and Centers of Gravity of a Vessel

Significance and Use

4.1 From the light ship characteristics one is able to calculate the stability characteristics of the vessel for all conditions of loading and thereby determine whether the vessel satisfies the applicable stability criteria. Accurate results from a stability test may in some cases determine the future survival of the vessel and its crew, so the accuracy with which the test is conducted cannot be overemphasized. The condition of the vessel and the environment during the test is rarely ideal and consequently, the stability test is infrequently conducted exactly as planned. If the vessel is not 100 % complete and the weather is not perfect, there ends up being water or shipyard trash in a tank that was supposed to be clean and dry and so forth, then the person in charge must make immediate decisions as to the acceptability of variances from the plan. A complete understanding of the principles behind the stability test and a knowledge of the factors that affect the results is necessary.

1.1 This guide covers the determination of a vessel’s light ship characteristics. In this standard, a vessel is a traditional hull-formed vessel. The stability test can be considered to be two separate tasks; the lightweight survey and the inclining experiment. The stability test is required for most vessels upon their completion and after major conversions. It is normally conducted inshore in calm weather conditions and usually requires the vessel be taken out of service to prepare for and conduct the stability test. The three light ship characteristics determined from the stability test for conventional (symmetrical) ships are displacement (“ displ ”), longitudinal center of gravity (“ LCG ”), and the vertical center of gravity (“ KG ”). The transverse center of gravity (“ TCG ”) may also be determined for mobile offshore drilling units (MODUs) and other vessels which are asymmetrical about the centerline or whose internal arrangement or outfitting is such that an inherent list may develop from off-center weight. Because of their nature, other special considerations not specifically addressed in this guide may be necessary for some MODUs. This standard is not applicable to vessels such as a tension-leg platforms, semi-submersibles, rigid hull inflatable boats, and so on.

1.2 The limitations of 1 % trim or 4 % heel and so on apply if one is using the traditional pre-defined hydrostatic characteristics. This is due to the drastic change of waterplane area. If one is calculating hydrostatic characteristics at each move, such as utilizing a computer program, then the limitations are not applicable.

1.3 The values stated in inch-pound units are to be regarded as standard. No other units of measurement are included in this standard.

1.3.1 Exceptions— Other units may be used for the stability test, but the test results should be reported in the same units and coordinate system as the vessel’s draft marks and Trim and Stability Book or similar stability information provided.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Why Redline?

A PDF redline is a quick and easy way to compare all of the changes between the current, active standard and the previous version.

and other changes between the two standards.

Save Time and Trouble! With a Redline you no longer have to spend time trying to determine what has changed in the new standard! Redlines save you time and ensure you see what the changes are to the standard.

Price When you select the "Standard + Redline" option you get both documents! Best of all, the cost of a Standard + Redline is only slightly more than buying the Active Standard by itself.

ASTM Shipping and Handling

Domestic Shipping

Domestic orders are delivered via United Parcel Service (UPS) or United States Postal Service (USPS). Transit times average 3 to 5 business days. Please be aware that UPS will not deliver packages to Post Office Boxes.

Domestic Rush Orders

Please Contact Us .

International Standard Shipping

International orders are delivered via courier post services which can be either a postal service, courier service, or a combination of both. Standard Service is untraceable. Please allow 4-7 weeks for delivery.

International Expedited Shipping

Please be aware that carriers will not deliver packages to Post Office Boxes. Because of the variability of customs processes and procedures in different countries, ASTM International cannot guarantee transit times to international destinations. Customs duty and taxes are the responsibility of the consignee.

Shipping & Handling charges follow the rate schedule, below:

Order Total	Shipping & Handling Fee
Up to $50.00	$9.04
$50.01 to $100.00	$17.88
$100.01 to $150.00	$26.33
$150.01 to $250.00	$35.18
$250.01 to $500.00	$51.05
$500.01 to $750.00	$69.69
$750.01 to $1000.00	$85.16
$1000.01 to $1500.00	$111.16
$1500.01 to $2500.00	$145.47
$2500.01 to $4999.00	$192.31
$5000.00 to $higher	$FREE

Shipping and Handling charges are approximate. Additional charges may be incurred if your order requires multiple shipments. This does not apply to complete sets and sections.

ASTM License Agreement

IMPORTANT- READ THESE TERMS CAREFULLY BEFORE ENTERING THIS ASTM PRODUCT. By purchasing a subscription and clicking through this agreement, you are entering into a contract, and acknowledge that you have read this License Agreement, that you understand it and agree to be bound by its terms. If you do not agree to the terms of this License Agreement, promptly exit this page without entering the ASTM Product.

1. Ownership: This Product is copyrighted, both as a compilation and as individual standards, articles and/or documents ("Documents") by ASTM ("ASTM"), 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959 USA, except as may be explicitly noted in the text of the individual Documents. All rights reserved. You (Licensee) have no ownership or other rights in the ASTM Product or in the Documents. This is not a sale; all right, title and interest in the ASTM Product or Documents (in both electronic file and hard copy) belong to ASTM. You may not remove or obscure the copyright notice or other notice contained in the ASTM Product or Documents.

2. Definitions.

A. Types of Licensees:

(i) Individual User: a single unique computer, with an individual IP address;

(ii) Single-Site: one geographic location or to multiple sites within one city that are part of a single organization unit administered centrally; for example, different campuses of the same university within the same city administered centrally.

(iii) Multi-Site: an organization or company with independently administered multiple locations within one city; or an organization or company located in more than one city, state or country, with central administration for all locations.

B. Authorized Users: any individual who has subscribed to this Product; if a Site License, also includes registered students, faculty or staff member, or employee of the Licensee, at the Single or Multiple Site.

3. Limited License. ASTM grants Licensee a limited, revocable, nonexclusive, non-transferable license to access, by means of one or more authorized IP addresses, and according to the terms of this Agreement, to make the uses permitted and described below, each ASTM Product to which Licensee has subscribed.

A. Specific Licenses:

(i) Individual User:

(a) the right to browse, search, retrieve, display and view the Product;

(b) the right to download, store or print single copies of individual Documents, or portions of such Documents, solely for Licensee's own use. That is, Licensee may access and download an electronic file of a Document (or portion of a Document) for temporary storage on one computer for purposes of viewing, and/or printing one copy of a Document for individual use. Neither the electronic file nor the single hard copy print may be reproduced in anyway. In addition, the electronic file may not be distributed elsewhere over computer networks or otherwise. That is, the electronic file cannot be emailed, downloaded to disk, copied to another hard drive or otherwise shared. The single hard copy print may only be distributed to others for their internal use within your organization; it may not be copied. The individual Document downloaded may not otherwise be sold or resold, rented, leased, lent or sub-licensed.

(ii) Single-Site and Multi-Site Licenses:

(b) the right to download, store or print single copies of individual Documents, or portions of such Documents for the Authorized User's personal use, and to share such copies with other Authorized Users of Licensee within Licensee's computer network;

(c) if an educational institution, Licensee is permitted to provide a hard copy of individual Documents to individual students (Authorized Users) in a class at Licensee's location;

(d) the right to display, download and distribute hard copies of Documents for training Authorized Users or groups of Authorized Users.

(e) Licensee will undertake all necessary authentication and verification processes to ensure only Authorized Users can access the ASTM Product.

(f) Licensee will provide ASTM with a list of authorized IP (numeric IP domain addresses) addresses and, if Multi-Site, a list of authorized sites.

B. Prohibited Uses.

(i) This License describes all permitted uses. Any other use is prohibited, is a violation of this Agreement and can result in immediate termination of this License.

(ii) An Authorized User may not make this Product, or Documents, available to anyone other than another Authorized User, whether by Internet link, or by permitting access through his or her terminal or computer; or by other similar or dissimilar means or arrangements.

(iii) Specifically, no one is authorized to transmit, copy, or distribute any Document in any manner or for any purpose except as described in Section 3 of this License, without ASTM's prior express written permission. In particular, except as described in Section 3, no one may, without the prior express written permission of ASTM: (a) distribute or forward a copy (electronic or otherwise) of any article, file, or material obtained from any ASTM Product or Document; (b) reproduce or photocopy any standard, article, file, or material from any ASTM Product; (c) alter, modify, adapt, or translate any standard, article, file, or material obtained from any ASTM Product; (d) include any standard, article, file, or material obtained from any ASTM Product or Document in other works or otherwise create any derivative work based on any materials obtained from any ASTM Product or Document; (e) impose any charge for a copy (electronic or otherwise) of any standard,article, file, or material obtained from any ASTM Product or Document, except for normal printing/copying costs where such reproduction is authorized under Section 3; or (f) systematically download, archive, or centrally store substantial portions of standards, articles, files, or material obtained from any ASTM Product or Document. Inclusion of print or electronic copies in coursepacks or electronic reserves, or for distance learning use, is not authorized by this License and is prohibited without ASTM's prior written permission.

(iv) Licensee may not utilize the Product, or access to the Product, for commercial purposes, including but not limited to the sale of Documents, materials, fee-for-service use of the Product or bulk reproduction or distribution of Documents in any form; nor may Licensee impose special charges on Authorized Users for use of the Product beyond reasonable printing or administrative costs.

C. Copyright Notice . All copies of material from an ASTM Product must bear proper copyright notice in ASTM's name, as shown in the initial page of each standard, article, file or material. Obscuring, deletion or modification of the copyright notice is not permitted.

4. Detection of Prohibited Uses.

A. Licensee is responsible for taking reasonable measures to prevent prohibited uses, and promptly notify ASTM of any infringements of copyright or prohibited use of which Licensee becomes aware. Licensee will cooperate with ASTM in investigating any such prohibited uses and will take reasonable steps to ensure the cessation of such activity and to prevent any reoccurrence.

B. Licensee shall use all reasonable efforts to protect the Product from any use that is not permitted under this Agreement, and shall notify ASTM of any use of which it learns or is notified.

5. Continued Access to Product. ASTM reserves the right to terminate this License, upon written notice, if Licensee materially breaches the terms of this Agreement. If Licensee fails to pay ASTM any license or subscription fees when due, ASTM will provide the Licensee with a 30-day period within which to cure such breach. No cure period will be provided for material breaches relating to violations of Section 3 or any other breach likely to cause ASTM irreparable harm. If Licensee's subscription to an ASTM Product terminates, further access to the online database will be denied. If Licensee or Authorized Users materially breach this License or make prohibited uses of material in any ASTM Product, ASTM reserves the right to deny Licensee any access to the ASTM Product, in ASTM's sole discretion.

6. Delivery Formats and Service.

A. Some ASTM Products use standard Internet HTML format. ASTM reserves the right to change such format upon three [3] months' notice to Licensee, although ASTM will make reasonable efforts to use commonly available formats. The Licensee and the Authorized Users are responsible for obtaining at their expense suitable Internet connections, Web browsers, and licenses for any software necessary to view the ASTM Products.

B. The ASTM Products are also available in Adobe Acrobat (PDF) format to Licensee and its Authorized Users, who are solely responsible for installing and configuring the appropriate Adobe Acrobat Reader software.

C. ASTM shall use reasonable efforts to make online access available on a continuous basis. Availability will be subject to periodic interruption and downtime for server maintenance, software installation or testing, loading new files, and reasons beyond the control of ASTM. ASTM does not guarantee access, and will not be liable for damages or refunds if the Product becomes unavailable temporarily, or if access becomes slow or incomplete due to system back-up procedures, Internet traffic volume, upgrades, overload of requests to servers, general network failures or delays, or any other cause that may from time to time make the Product unavailable for the Licensee or Licensee's Authorized Users.

7. Terms and Fees.

A. The term of this Agreement is _____________ ("Subscription Period"). Access to the Product is for the Subscription Period only. This Agreement will remain in effect thereafter for successive Subscription Periods so long as annual subscription fees, as such may change from time to time, are paid. Licensee and/or ASTM have the right to terminate this Agreement at the end of a Subscription Period by written notice given at least 30 days in advance.

8. Verification. ASTM has the right to verify compliance with this Agreement, at its expense, and at any time during the course of normal business hours. To do so, ASTM will engage an independent consultant, subject to a confidentiality agreement, to review Licensee's use of ASTM Product and/or Documents. Licensee agrees to permit access to its information and computer systems for this purpose. Verification will take place upon no less than 15 days notice, during normal business hours and in a manner that does not interfere unreasonably with Licensee's operations. If verification reveals unlicensed or prohibited use of the ASTM Products or Documents, Licensee agrees to reimburse ASTM for the costs incurred in verification and reimburse ASTM for any unlicensed/prohibited uses. By invoking this procedure, ASTM does not waive any of its rights to enforce this Agreement or to protect its intellectual property by any other means permitted by law. Licensee acknowledges and agrees that ASTM may imbed certain identifying or tracking information in the ASTM Products available on the Portal.

9. Passwords: Licensee must immediately notify ASTM of any known or suspected unauthorized use(s) of its password(s), or any known or suspected breach of security, including the loss, theft unauthorized disclosure of such password or any unauthorized access to or use of the ASTM Product. Licensee is solely responsible for maintaining the confidentiality of its password(s) and for ensuring the authorized access and use of the ASTM Product. Personal accounts/passwords may not be shared.

10. Disclaimer of Warranty: Unless specified in this Agreement, all express or implied conditions, representations and warranties, including any implied warranty of merchantability, fitness for a particular purpose or non-infringement are disclaimed, except to the extent that these disclaimers are held to be legally invalid.

11. Limitation of Liability: To the extent not prohibited by law, in no event will ASTM be liable for any loss, damage, lost data or for special, indirect, consequential or punitive damages, however caused regardless of the theory of liability, arising out of or related to the use of the ASTM Product or downloading of the ASTM Documents. In no event will ASTM's liability exceed the amount paid by Licensee under this License Agreement.

12. General.

A. Termination: This Agreement is effective until terminated. Licensee may terminate this Agreement at any time by destroying all copies (hard, digital or in any media)of the ASTM Documents and terminating all access to the ASTM Product.

B. Governing Law, Venue, and Jurisdiction: This Agreement shall be interpreted and construed in accordance with the laws of the Commonwealth of Pennsylvania. Licensee agrees to submit to jurisdiction and venue in the state and federal courts of Pennsylvania for any dispute which may arise under this Agreement. Licensee also agrees to waive any claim of immunity it may possess.

C. Integration: This Agreement is the entire agreement between Licensee and ASTM relating to its subject matter. It supersedes all prior or contemporaneous oral or written communications, proposals, representations and warranties and prevails over any conflicting or additional terms of any quote, order, acknowledgment, or other communication between the parties relating to its subject matter during the term of this Agreement. No modification of this Agreement will be binding, unless in writing and signed by an authorized representative of each party.

D. Assignment: Licensee may not assign or transfer its rights under this Agreement without the prior written permission of ASTM.

E. Taxes. Licensee must pay any applicable taxes, other than taxes on ASTM's net income, arising out of Licensee's use of the ASTM Product and/or rights granted under this Agreement.

Reprints and Permissions

Privacy Policy
Copyright/Permissions
Reading Room

Oral / interview questions
Written papers
Latest developments
Latest technical developments
Future Fuels
MARINE MAGAZINE
Marine news
THE MARINE MAGAZINE
Sign in / Join

Knowledge material
Marine Exams

INCLINING EXPERIMENT

This experiment is carried out on new ships and those that have had large structural alterations made, to find out the new centre of gravity (kg) and metacentric height (gm) and further to know the stability of the ship.

INCLINING EXPERIMENT:

During the experiment one or more weights are moved through a known distance ‘l’, transversely across the deck.
The resulting angle of heel ‘ǿ’ is measured by means of two pendulum, one at each end of the ship (or by using an instrument known as stabilograph).
When pendulum is used, deflection of pendulum is measured against a wooden batten.

Note : pendulum should be as long as possible, to improve the accuracy of measurement, and a fine wire with heavy bob to ensure free movement. The bob may be immersed in oil or water to dampen it’s movement.

Refer to figure,

as mass ‘W’ is moved across the deck through a distsnce ‘L’, the centre of gravity of the ship moves from ‘G’ to ‘G 1 ’.

therefore

W x L = ∆ x GG 1 ————————————(1)

where ∆ = displacement

with this ship will be inclined to some angle ‘ǿ’ and will be in stable equilibrium state. The centre of buoyancy will move from ‘B’ to ‘B 1 ’, vertically beneath G 1 .The movement of ‘GG 1 ’ is parallel to the movement of ‘W’ and therefore angle ‘G 1 GM’ is right angle.

therefore

GG 1 = GM x tanǿ ——————————–(2)

CONDUCTING INCLINING EXPERIMENT

The inclining experiment is carried out on the ship when it is as near complete as possible and in almost light weight condition. Because with light weight condition any adjustment on load can be made to establish the centre of gravity.
Procedure :
Two sets of weights are used, one on each side of the ship.
The inclination for the movement of each weights both to port, then back again and then to starboard and back again is noted.
Displacement of the ship is determined by noting the draught of ship & the specific gravity of water in which ship is floating.

PRECAUTIONS DURING EXPERIMENT

A calm day with no wind should be chosen
The ship should be free to move with all the moorings slack.
Any loose items should be secured.
All tanks should be empty or full to avoid free surface effect.
As few personnel as possible should be on board and they should be on the centreline of ship, when readings are being taken.
A large trim should be avoided.
The Metacentric height of the ship plays an important role in determining the loading capacity and stability of the ship. The Initial metacentric height of the ship is determined by an inclining experiment after the ship is completely built in the yard

Abstract and Figures

Discover the world's research

25+ million members
160+ million publication pages
2.3+ billion citations
Lovro Radoš

Dunja Legović

Levi Altschul
Nana Okra Kwadwo Abankwa
Miranda Vidhaj
Kristofor Lapa

RenQing Zhu

JungHwi Kim
DongHyup Youn
Michael D. Woodward

Keith W. Hutchinson
Andrew Scott
R.J. Dunworth
Recruit researchers
Join for free
Login Email Tip: Most researchers use their institutional email address as their ResearchGate login Password Forgot password? Keep me logged in Log in or Continue with Google Welcome back! Please log in. Email · Hint Tip: Most researchers use their institutional email address as their ResearchGate login Password Forgot password? Keep me logged in Log in or Continue with Google No account? Sign up

Inclining experiment

The shipyard carries out Inclining experiment to obtain accurately the vertical height of the center of gravity above the keel ( KG ).
A plumb line is suspended on the center line from a hatch coaming and allowed to move over a horizontal bed in the lower hold when a known weight w is shifted at its edges.

The length of the plumb line is I and the distance the plumb line is deflected is X . The GM is then subtracted from the KM calculate for the draft at the time of the experiment and does the line KG obtained. Once the KG has been obtained, that can easily be adjusted in the usual way for any changes of weight on board.
Light ship KG is provided onboard along with a statement setting up clearly items on board for that position of g .
It is usually stated for the Ship equipped ready for sea, with water in boiler but no bunkers (fresh or feed water) stores coolant effects.

For the experiment to be reliable you will have to ensure that

There is no wind. If there is wind the ship should be head to wind.
There is sufficient slack in the mooring and the ship is clear of the quay so that it can list freely.
The draught and density forward, aft and amidships are carefully noted that so that W and KM can be accurately determined
The ship is upright at the beginning of the experiment.
Only people directly concerned with the test should be on board.
When the weights are shifted the people onboard should stand on the center-line.
The amount of weight shifted should result in ship listing to about 4 degrees.
There is no free surface of liquid in the ship. Boilers and tanks are either full or empty.
Bilges are empty.
There are no loose weights on board.

On completion of this explanation you will know the procedure of mandated by intact stability code on preparations and procedure for the conduct of the inclining test.
The ship is moored in deep, sheltered, quiet waters where she can be inclined freely without coming into contact with either the berth or the bottom.
Moorings should allow unrestricted movement but also provide proper restraint to the vessel.
Tanks are either pressed or emptied and stripped to minimize free surface effect.

Inclining should be carried out by shifting weights.

Ship should be upright with all the weights to be shifted in position.
Transferring ballast to list the vessel may be allowed if the administration grants permission.

Weight should not be of the type that can absorb water (e.g., pororus).
They should be sufficient to incline the vessel by 1°- 4° so that there is no change in the shape or size of the water plane of the ship during the test.
Pendulums are the preferred method of measuring inclination deflections.

U-tubes and Inclinometer/pendulum combination may be used with authorisation of the administration.

Pendulums should be positioned so as to allow deflections of upto 15 CM on either side for an inclination of 4 degrees.
Pendulums should be made of piano wire or mono filament wire and be 4-6 meters in length.

Pendulum length is accurately measured and recorded.
3 pendulums (min 2) are set up as in figure:

A trough filled with water is provided to dampen oscillations.
Deflection are measured by Engineering scales after the deflection is marked on the batten.

Before commencing the inclination the dock water density is measured with an accurate hydrometer.

Inclining weights are marked with their weight and position before being placed on board.

A set of 5 free-boards on either side or 6 draft (forward, Aft and Midships) are taken to obtain an accurate displacement from the hydro static tables.

Vessel is inspected to check that there are no items that could shift during the installation.
Weights are moved transversely in the same direction so that the vessels trim does not change.
8 movements are made and deflections recorded. On completion of all movements of weights the ship should again be upright.

Movement of weight, deflection and the resultant value of tanφ (Deflection/Length of Pendulum) are recorded and plotted as follows for each movement.

A straight line passing through the center indicates a perfect inclination i.e.,
No free surface, bottom touching or wind.
Data is recorded in the presence of the authorized representative of the administration.

No comments

Adertisement, buy at amazon, maritime news, contact form, blog archive.

RECREATIONAL ITEMS
MEO Class 4 preparation Notes by Nithin
IMPORTANT REFERENCE BOOKS FOR GME (GRADUATE MARINE...
ELECTRICAL ORAL NOTES PREPARED BY SAMUDRA INSTITUTE
Complete List Of courses for Indian seafarers , an...
Function : 6 - MEO Class 4 Orals : MEP or MROL [Maintenance and Repairs at Operational Level]
Function : 4b - MEO Class 4 Orals : MOTOR or MEOL[Marine Engineering at Operational Level]
Function : 3 - MEO Class 4 Orals : SAFETY or COSCOPOOL
Function : 5 - MEO Class 4 Orals: Electrical or( EECEOL)
MEK (Motor) - written
Marine Electro Technology - written
MEP - written
NAVAL ARCH NUMERICAL.
Ship Construction and Stability (Naval Arch) -written
Ship Safety and Environmental Protection - written
MEK (General) - written
MEO Class 4 Orals questions asked mostly by surveyors in all MMD orals.

Clasification Society 2024 - Version 9.40
Preparations for the Inclining Test Free surface and tankage 2.1.1 If there are liquids on board the ship when it is inclined, whether in the bilges or in the tanks, they will shift to the low side when the ship heels. This shift of liquids will exaggerate the heel of the ship. Unless the exact weight and distance of liquid shifted can be precisely calculated, the metacentric height (GM) calculated from the inclining test will be in error. Free surface should be minimized by emptying the tanks completely and making sure all bilges are dry; or by completely filling the tanks so that no shift of liquid is possible. The latter method is not the optimum because air pockets are difficult to remove from between structural members of a tank, and the weight and centre of the liquid in a full tank should be accurately determined in order to adjust the lightship values accordingly. When tanks must be left slack, it is desirable that the sides of the tanks be parallel vertical planes and the tanks be regular in shape (i.e. rectangular, trapezoidal, etc.) when viewed from above, so that the free surface moment of the liquid can be accurately determined. For example, the free surface moment of the liquid in a tank with parallel vertical sides can be readily calculated by the formula: = length of tank (m) = breadth of tank (m) = specific gravity of liquid in tank (t/m³) = free surface moment (mt) Free surface correction is independent of the height of the tank in the ship, location of the tank, and direction of heel. As the width of the tank increases, the value of free surface moment increases by the third power. The distance available for the liquid to shift is the predominant factor. This is why even the smallest amount of liquid in the bottom of a wide tank or bilge is normally unacceptable and should be removed prior to the inclining experiment. Insignificant amounts of liquids in V-shaped tanks or voids (e.g., a chain locker in the bow), where the potential shift is negligible, may remain if removal of the liquid would be difficult or would cause extensive delays. When ballast water is used as inclining weight, the actual transverse and vertical movements of the liquid should be calculated taking into account the change of heel of the ship. Free surface corrections as defined in this paragraph should not apply to the inclining tanks. 2.1.2 : The number of slack tanks should normally be limited to one port/starboard pair or one centreline tank of the following: fresh water reserve feed tanks; fuel/diesel oil storage tanks; fuel/diesel oil day tanks; lube oil tanks; sanitary tanks; or potable water tanks. To avoid pocketing, slack tanks should normally be of regular (i.e. rectangular, trapezoidal, etc.) cross section and be 20% to 80% full if they are deep tanks and 40% to 60% full if they are double-bottom tanks. These levels ensure that the rate of shifting of liquid remains constant throughout the heel angles of the inclining test. If the trim changes as the ship is inclined, then consideration should also be given to longitudinal pocketing. Slack tanks containing liquids of sufficient viscosity to prevent free movement of the liquids, as the ship is inclined (such as bunker at low temperature), should be avoided since the free surface cannot be calculated accurately. A free surface correction for such tanks should not be used unless the tanks are heated to reduce viscosity. Communication between tanks should never be allowed. Cross-connections, including those via manifolds, should be closed. Equal liquid levels in slack tank pairs can be a warning sign of open cross connections. A bilge, ballast, and fuel oil piping plan can be referred to, when checking for cross connection closures. 2.1.3 : “Pressed up” means completely full with no voids caused by trim or inadequate venting. Anything less than 100% full, for example the 98% condition regarded as full for operational purposes, is not acceptable. Preferably, the ship should be rolled from side to side to eliminate entrapped air before taking the final sounding. Special care should be taken when pressing fuel oil tanks to prevent accidental pollution. An example of a tank that would appear “pressed up”, but actually contains entrapped air, is shown in . 2.1.4 It is generally not sufficient to simply pump tanks until suction is lost. Enter the tank after pumping to determine if final stripping with portable pumps or by hand is necessary. The exceptions are very narrow tanks or tanks where there is a sharp deadrise, since free surface would be negligible. Since all empty tanks should be inspected, all manholes should be open and the tanks well ventilated and certified as safe for entry. A safe testing device should be on hand to test for sufficient oxygen and minimum toxic levels. A certified marine chemist's certificate certifying that all fuel oil and chemical tanks are safe for human entry should be available, if necessary. Mooring arrangements The importance of good mooring arrangements cannot be overemphasized. The arrangement selections will be dependent upon many factors. Among the most important are depth of water, wind and current effects. Whenever possible, the ship should be moored in a quiet, sheltered area free from extraneous forces such as propeller wash from passing ships, or sudden discharges from shore side pumps. The depth of water under the hull should be sufficient to ensure that the hull will be entirely free of the bottom. The tide conditions and the trim of the ship during the test should be considered. Prior to the test, the depth of water should be measured and recorded in as many locations as necessary to ensure the ship will not contact the bottom. If marginal, the test should be conducted during high tide or the ship moved to deeper water. 2.2.1 The mooring arrangement should ensure that the ship will be free to list without restraint for a sufficient period of time to allow a satisfactory reading of the heeling angle, due to each weight shift, to be recorded. 2.2.2 The ship should be held by lines at the bow and the stern, attached to bollards and/or cleats on the deck. If suitable restraint of the ship cannot be achieved using deck fittings, then temporary padeyes should be attached as close as possible to the centreline of the ship and as near the waterline as practical. Where the ship can be moored to one side only, it is good practice to supplement the bow and stern lines with two spring lines in order to maintain positive control of the ship, as shown in . The leads of the spring lines should be as long as practicable. Cylindrical camels should be provided between the ship and the dock. All lines should be slack, with the ship free of the pier and camels, when taking readings. 2.2.2.1 If the ship is held off the pier by the combined effect of the wind and current, a superimposed heeling moment will act on the ship throughout the test. For steady conditions this will not affect the results. Gusty winds or uniformly varying wind and/or current will cause these superimposed heeling moments to change, which may require additional test points to obtain a valid test. The need for additional test points can be determined by plotting test points as they are obtained. 2.2.2.2 If the ship is pressed against the fenders by wind and/or current, all lines should be slack. The cylindrical camels will prevent binding but there will be an additional superimposed heeling moment due to the ship bearing against the camels. This condition should be avoided where possible but, when used, consideration should be given to pulling the ship free of the dock and camels and letting the ship drift as readings are taken. 2.2.2.3 Another acceptable arrangement is where the combined wind and current are such that the ship may be controlled by only one line at either the bow or the stern. In this case, the control line should be led from on or near the centreline of the ship with all lines but the control line slack, the ship is free to veer with the wind and/or current as readings are taken. This can sometimes be troublesome because varying wind and/or current can cause distortion of the plot. 2.2.3 The mooring arrangement should be submitted to the approval authority for review prior to the test. 2.2.4 If a floating crane is used for handling inclining weights, it should not be moored to the ship. Test weights 2.3.1 Weights, such as porous concrete, that can absorb significant amounts of moisture should only be used if they are weighed just prior to the inclining test or if recent weight certificates are presented. Each weight should be marked with an identification number and its weight. For small ships, drums completely filled with water may be used. Drums should normally be full and capped to allow accurate weight control. In such cases, the weight of the drums should be verified in the presence of the Administration representative using a recently calibrated scale. 2.3.2 Precautions should be taken to ensure that the decks are not overloaded during weight movements. If deck strength is questionable then a structural analysis should be performed to determine if existing framing can support the weight. 2.3.3 Generally, the test weights should be positioned as far outboard as possible on the upper deck. The test weights should be on board and in place prior to the scheduled time of the inclining test. 2.3.4 Where the use of solid weights to produce the inclining moment is demonstrated to be impracticable, the movement of ballast water may be permitted as an alternative method. This acceptance would be granted for a specific test only, and approval of the test procedure by the Administration is required. As a minimal prerequisite for acceptability, the following conditions should be required: inclining tanks should be wall-sided and free of large stringers or other internal members that create air pockets. Other tank geometries may be accepted at the discretion of the Administration; tanks should be directly opposite to maintain ship's trim; specific gravity of ballast water should be measured and recorded; pipelines to inclining tanks should be full. If the ship's piping layout is unsuitable for internal transfer, portable pumps and pipes/hoses may be used; blanks must be inserted in transfer manifolds to prevent the possibility of liquids being “leaked” during transfer. Continuous valve control must be maintained during the test; all inclining tanks must be manually sounded before and after each shift; vertical, longitudinal and transverse centres should be calculated for each movement; accurate sounding/ullage tables must be provided. The ship's initial heel angle should be established prior to the incline in order to produce accurate values for volumes and transverse and vertical centres of gravity for the inclining tanks at every angle of heel. The draught marks amidships (port and starboard) should be used when establishing the initial heel angle; verification of the quantity shifted may be achieved by a flow meter or similar device; and the time to conduct the inclining must be evaluated. If time requirements for transfer of liquids are considered too long, water may be unacceptable because of the possibility of wind shifts over long periods of time. Pendulums 2.4.1 The pendulums should be long enough to give a measured deflection, to each side of upright, of at least 15 cm. Generally, this will require a pendulum length of at least 3 m. It is recommended that pendulum lengths of 4 to 6 m be used. Usually, the longer the pendulum the greater the accuracy of the test; however, if excessively long pendulums are used on a tender ship the pendulums may not settle down and the accuracy of the pendulums would then be questionable. On large ships with high GM, pendulum lengths in excess of the length recommended above may be required to obtain the minimum deflection. In such cases, the trough, as shown in , should be filled with high-viscosity oil. If the pendulums are of different lengths, the possibility of collusion between station recorders is avoided. 2.4.2 On smaller ships, where there is insufficient headroom to hang long pendulums, the 15 cm deflection should be obtained by increasing the test weight so as to increase the heel. On most ships the typical inclination is between one and four degrees. 2.4.3 The pendulum wire should be piano wire or other monofilament material. The top connection of the pendulum should afford unrestricted rotation of the pivot point. An example is that of a washer with the pendulum wire attached suspended from a nail. 2.4.4 A trough filled with a liquid should be provided to dampen oscillations of the pendulum after each weight movement. It should be deep enough to prevent the pendulum weight from touching the bottom. The use of a winged plumb bob at the end of the pendulum wire can also help to dampen the pendulum oscillations in the liquid. 2.4.5 The battens should be smooth, light-coloured wood, 1 to 2 cm thick, and should be securely fixed in position so that an inadvertent contact will not cause them to shift. The batten should be aligned close to the pendulum wire but not in contact with it. 2.4.6 A typical satisfactory arrangement is shown in . The pendulums may be placed in any location on the ship, longitudinally and transversely. The pendulums should be in place prior to the scheduled time of the inclining test. 2.4.7 It is recommended that inclinometers or other measuring devices only be used in conjunction with at least one pendulum. The Administration may approve an alternative arrangement when this is found impractical. U-tubes 2.5.1 The legs of the device should be securely positioned as far as outboard as possible and should be parallel to the centreline plane of the ship. The distance between the legs should be measured perpendicular to the centreline plane. The legs should be vertical, as far as practical. 2.5.2 Arrangements should be made for recording all readings at both legs. For easy reading and checking for air pockets, clear plastic tube or hose should be used throughout. The U-tube should be pressure-tested prior to the inclining test to ensure watertightness. 2.5.3 The horizontal distance between the legs of the U-tube should be sufficient to obtain a level difference of at least 15 cm between the upright and the maximum inclination to each side. 2.5.4 Normally, water would be used as the liquid in the U-tube. Other low-viscosity liquids may also be considered. 2.5.5 The tube should be free of air pockets. Arrangements should be made to ensure that the free flow of the liquid in the tube is not obstructed. 2.5.6 Where a U-tube is used as a measuring device, due consideration should be given to the prevailing weather conditions (see 4.1.1.3): if the U-tube is exposed to direct sunlight, arrangements should be made to avoid temperature differences along the length of the tube; if temperatures below 0°C are expected, the liquid should be a mixture of water and an anti-freeze additive; and where heavy rain squalls can be expected, arrangements should be made to avoid additional water entering the U-tube. Inclinometers The use of inclinometers should be subject to at least the following recommendations: the accuracy should be equivalent to that of the pendulum; the sensitivity of the inclinometer should be such that the non-steady heeling angle of the ship can be recorded throughout the measurement; the recording period should be sufficient to accurately measure the inclination. The recording capacity should be generally sufficient for the whole test; the instrument should be able to plot or print the recorded inclination angles on paper; the instrument should have linear performance over the expected range of inclination angles; the instrument should be supplied with the manufacturer's instructions giving details of calibration, operating instructions, etc.; and it should be possible to demonstrate the required performance to the satisfaction of the Administration during the inclining test.

View PDF
Download full issue

Ocean Engineering

Uncertainty analysis procedure for the ship inclining experiment.

• Procedure for evaluating and reducing uncertainty in the inclining experiment.
• For some ships, a substantial increase in the minimum GM ¯ may be necessary.
• A complete procedure for establishing the uncertainty in GM ¯ for any load condition.
Previous article in issue
Next article in issue

Cited by (0)

MEO Class 4
_Epareeksha MCQ
Machineries
_Main Engine
_Aux Engine (D/G)
_Air Compressor
_Freshwater Generator
_Hydrophore
_Refrigeration
Naval Arch.
Electricity

Inclining Experiment Theory And Explanation

Inclining experiment is conducted by the shipyard to determine the metacentric height(KM), and hence the height of the center of gravity (KG) of the ship. If the height of the center of gravity of the empty ship is known, it is possible to calculate its position for any given condition of loading.

The experiment is conducted on an empty ship ( with minimum personal to conduct experiment). A small mass m is moved across the ship through a distance d. This causes the center of gravity to move from its original position G on the centerline to G1.

If Δ = displacement of ship

Then GG1 = m x d/Δ---- (1)

When the center of buoyancy changes from B to B1, the ship heels to an angle θ

From the above diagram

GG1 = GM tan θ---- (2)

GM tan θ= m x d/Δ--- from (1) and (2)

GM= m x d/Δ tan θ

In the above equation the only unknown value is θ . To determine the angle of the heel θ, suspend a pendulum. The deflection of the pendulum may be measured when the mass is moved across the deck.

Thus if L = length of pendulum

tan θ = a/L

and GM = m x d x L/(Δ x a)

The height of the transverse metacenter above the keel may be found from the metacentric diagram and hence the height of the center of gravity of the ship may be determined.

KG = KM — GM

Contact Form

IMAGES

Inclining experiment
Inclining experiment
Inclining Experiment Procedure for Ship
Inclining Experiment
Inclining experiment
Inclining experiment

VIDEO

Inclining Experiment
Vessel Inclining
Shipyard Inclining Experiment
Inclining Experiment Phase 2
Inclining Experiment/ Naval Arc 2 / Stability/ MMD Past pape4 Solution/ Ch mate phase 2
To assist of Eng'r. Francisco who will conduct vessel inclining tes

COMMENTS

Inclining Experiment- Determining Metacentric height of the ship
The metacentric height is the distance between the centre of gravity and metacentre of the ship i.e. GM and it is used to calculate the stability of the ship. Inclining Experiment. Requirements. The experiment is carried out when the ship is built completely or when major structural changes have been done. The experiment is carried out with ...
The Inclining Experiment
The inclining test is carried out to find the lightship KG at the lightship displacement. It is sometimes known as a ' controlled list experiment '. By conducting the experiment by means of a series of weight shifts, the GM of the vessel can be ascertained under the test condition. This GM value can then be compared with the ship's KM to ...
Ship Stability: Intact Stability Criteria and Inclining Experiment
The Inclining Experiment: ... Like say for example, a vessel with the displacement of 4950 t, which is initially upright when a weight of 25 t is moved across the deck 9.14m and at the same time a plumb line of 4.26m in length is deflected 0.3m. Find the GM. GM = (w × d × Original Length) ÷ (Displacement × Deflection) ...
Inclining Experiment
To determine the position of the vertical centre of gravity an inclining experiment is carried out. The immediate purpose of the experiment is to determine the metacentric height. ... The hog or sag of the vessel is thus determined, and also the initial list, if any. The density of the water in which the ship is floating should be determined by ...
Inclining test
An inclining test is a test performed on a ship to determine its stability, lightship weight and the coordinates of its center of gravity. The test is applied to newly constructed ships greater than 24m in length, and to ships altered in ways that could affect stability. ... The weight of a vessel can be readily determined by reading draughts ...
PDF EN400 LAB #3 PRELAB INCLINING EXPERIMENT
It is used to record the tangent of the inclining angle. Figure 1 Inclining Apparatus 3. On Figure 1, show the inclining angle (φ) and the adjacent and opposite sides (dadj and dopp) to the triangle that allows the calculation of tan φ. Based on the geometry, give the equation for tan φ in terms of these quantities.
Tearing down the wall
1. Introduction. The inclining experiment is the primary method available for determining the vertical centre of gravity V C G, of the lightship of a vessel upon completion and to keep track of any changes in V C G through the vessel's life. There are alternatives such as the roll period test, but no other method is as feasible and as broadly accepted as the classical inclining experiment in ...
PDF Tearing down the wall
1. Introduction. The inclining experiment is the primary method available for determining the vertical centre of. gravity, , of the lightship of a vessel upon completion and to keep track of any changes in. through the vessel's life. There are alternatives such as the roll period test, but no other method is.
Inclining Experiment
In this video. I discuss the procedure to conduct the inclining experiment, the formula derived from the experiment, and the precautions to be observed when ...
Inclining Experiment
THE INCLINING EXPERIMENT. It has been shown that, although much of the data used in stability calculations depends only on the geometry of the ship, the position of the centre of gravity must be known before the stability can be assessed finally for a given ship condition. ... The density of the water in which the vessel is floating is measured ...
Beyond the metacentre
The lightship characteristics measured by inclining experiment are a fundamental input to managing a ship's intact and damage stability throughout its service life or until it is re-inclined. ... Inclining Experiment Analysis on Vessels with Chines, Hull Discontinuities or Asymmetry, The Australian Naval Architect, Sydney, Australia, November ...
Naval architecture
Inclining experiment. Fortunately, the naval architect is able to make a full-scale check of the predicted or calculated metacentric stability before the completed ship goes to sea. By shifting liquids or solid masses whose weights and offset positions are known accurately, the centre of gravity of the whole ship is shifted and the ship is heeled.
Annex 1
Statutory Documents - IMO Publications and Documents - International Codes - 2008 IS Code - International Code on Intact Stability, 2008 - Part B - Recommendations for ships engaged in certain types of operations, certain types of ships and additional guidelines - Annex 1 - Detailed Guidance for the Conduct of an Inclining Test
F1321 Standard Guide for Conducting a Stability Test (Lightweight
1.1 This guide covers the determination of a vessel's light ship characteristics. In this standard, a vessel is a traditional hull-formed vessel. The stability test can be considered to be two separate tasks; the lightweight survey and the inclining experiment.
Tearing down the wall
Introduction. The inclining experiment is the primary method available for determining the vertical centre of gravity V C G, of the lightship of a vessel upon completion and to keep track of any changes in V C G through the vessel's life. There are alternatives such as the roll period test, but no other method is as feasible and as broadly accepted as the classical inclining experiment in use ...
INCLINING EXPERIMENT
The inclining experiment is carried out on the ship when it is as near complete as possible and in almost light weight condition. Because with light weight condition any adjustment on load can be made to establish the centre of gravity. Two sets of weights are used, one on each side of the ship. The inclination for the movement of each weights ...
PDF Uncertainty analysis procedure for the ship inclining experiment
Inclining experiment Uncertainty analysis Ship stability KG GM. The inclining experiment is typically performed for all new-build ships and after any major refit. The purpose of the inclining experiment is to establish the vertical distance of the centre-of-mass of the ship above its keel in the lightship condition.
Reliability analysis of GM and KG of ships from the inclining experiment
A sample sequence. of the shifts is shown in Figure 1. Since the inclining test yields GM of a ship directly, vertical position of center of gravit y can be calculated. from the difference, as ...
(PDF) Tearing down the wall
The inclining experiment is the primary method available for determining the vertical centre of. gravity, , of the lightship of a vessel upon completion and to keep track of any changes in ...
Inclining experiment
Inclining experiment. The shipyard carries out Inclining experiment to obtain accurately the vertical height of the center of gravity above the keel (KG). A plumb line is suspended on the center line from a hatch coaming and allowed to move over a horizontal bed in the lower hold when a known weight w is shifted at its edges. The length of the ...
2 Preparations for the Inclining Test
The U-tube should be pressure-tested prior to the inclining test to ensure watertightness. 2.5.3 The horizontal distance between the legs of the U-tube should be sufficient to obtain a level difference of at least 15 cm between the upright and the maximum inclination to each side.
Uncertainty analysis procedure for the ship inclining experiment
The purpose of the inclining experiment is to establish the vertical distance of the centre-of-mass of the ship above its keel in the lightship condition. This value is then taken as the point of reference when loading the ship, for establishing the 'in-service' stability, throughout the life of the ship. Experimental uncertainty analysis ...
Inclining Experiment Theory And Explanation
Inclining experiment is conducted by the shipyard to determine the metacentric height (KM), and hence the height of the center of gravity (KG) of the ship. If the height of the center of gravity of the empty ship is known, it is possible to calculate its position for any given condition of loading. The experiment is conducted on an empty ship ...