Page 67 - Introduction to Naval Architecture

54 FLOTATION AND STABILITY

Figure 4.18 Inclining experiment

alongside sets 3 and 4. G moves to GI as the ship inclines to a small
angle and B moves to Bj . It follows that:

<p can be obtained in a number of ways. The commonest is to use two
long pendulums, one forward and one aft, suspended from the deck
into the holds. If d and / are the shift and length of a pendulum
respectively, tan <p = d/L
To improve the accuracy of the experiment, several shifts of weight
are used. Thus, after set 1 has been moved, a typical sequence would be
to move successively set 2, replace set 2 in original position followed by
set 1 . The sequence is repeated for sets 3 and 4. At each stage the angle
of heel is noted and the results plotted to give a mean angle for unit
applied moment. When the metacentric height has been obtained, the
height of the centre of gravity is determined by subtracting GM from
the value of ,KM given by the hydrostatics for the mean draught at which
the ship was floating. This KG must be corrected for the weights to go
on and come off. The longitudinal position of B, and hence G, can be
found using the recorded draughts.
To obtain accurate results a number of precautions have to be
observed. First the experiment should be conducted in calm water with
little wind. Inside a dock is good as this eliminates the effects of tides
and currents. The ship must be floating freely when records are taken
so any mooring lines must be slack and the brow must be lifted clear. All
weights must be secure and tanks must be empty or pressed full to avoid