Outline of Procedure (for guidance only)
The following notes assume that a lines plan is available and is suitable for entering into a computer and are for general guidance only.
The vessel should be as near complete as possible and in a condition which reflects her usual state. The tanks (fuel, fresh water, ballast, black water, grey water etc…) must be either completely full or completely empty. All tanks will have to be opened up at the Inclining to confirm that they are empty or the sounding pipes sighted to confirm that they are full. The positions and sizes of all tanks will need to be measured if no tank plan is available.
During the Inclining Experiment, the draught at which the vessel is floating together with the trim needs to be known accurately. This can only really be achieved by using draught marks whose locations will also need to be known as accurately as possible. Ideally the draught marks positions should have been verified by this company or by another official body. If no draught marks are available then it may be possible to determine the draught by measuring the freeboard but this method leads to inaccuracies and is not particularly suitable for old wooden vessels which tend to twist and deform slightly with age. Otherwise, it may be prudent to slip the vessel and add draught marks. Vessels which carry more than 1,000 kg cargo are required to have draught marks.
Two pendulums will be required which can be provided by this company. They should be about 2 metres long and the bob should be immersed in a bucket or trough of oil to dampen the swing. A batten should be placed near the bottom of the pendulum on which paper can be pinned in order to record the deflections. The exact length of the pendulum will be recorded during the Inclining Experiment.
The specific gravity of the water in which the vessel is floating needs to be established using a hydrometer. This company has a hydrometer which covers the SGs required. [NOTE: A battery hydrometer is not adequate for this purpose].
The location and amount of internal ballast will need to be recorded.
A number of incline weights will be required to provide a suitable angle of heel. The amount of incline weight can be estimated by this company before carrying out the Inclining Experiment. The weights should be ideally be equal in weight and even in number. They will need to be positioned evenly on the port and starboard sides. The exact longitudinal, transverse and vertical position of the incline weights will be measured. During the Inclining Experiment each set of weights will be moved from one side to the other and then back again. The deflection of the pendulum will be recorded for each weight shift. The exact distance moved by each weight will be measured.
After the Inclining Experiment has been carried out the computer software will provide a table of Hydrostatics which will be used to calculate the stability. From the draught at which the vessel is floating (in the loaded condition), the Hydrostatics will indicate an initial displacement, longitudinal centre of buoyancy (LCB) and a transverse KM (the height of the metacentre above the base line). Using the deflections of the pendulum, a mean deflection per unit moment can be calculated together with an associated angle of heel. That will produce an initial metacentric height (for the loaded condition) above the centre of gravity (called the GM). Using the KM calculated from the Hydrostatics and GM calculated from the pendulum deflections, the vertical centre of gravity (KG) can be established.
The displacement, LCG, VCG with the incline weights removed can then be calculated. It is this value of the VCG (or KG) which is required for the Stability Booklet. Using this value, righting lever curves can be produced for any loading condition from which the Statutory Stability Book can be produced.