Page 446 - statbility for masters and mates

Appendix IX
Draft Surveys
When a ship loads up at a port, departs from this port and travels to another port, a Draft Survey is carried out. This is to check that the cargo deadweight or `constant' is satisfactory for the shipowner at the port of arrival.
It is virtually a check on the amount of cargo that left the ®rst port against that arriving at the second port. This Draft Survey may be carried out by a Master, a Chief Engineer or a Naval Architect.
Prior to starting on a Draft Survey the vessel should be in upright condition and on even keel if possible. If not on even keel then certainly within 1 per cent of her LBP would be advantageous.
When the ship arrives in port ready for this Draft Survey, there are several items of information that have to be known by, say, the Naval Architect. They include:
LBP and Cb relative to the ship's waterline or actual loaded condition. Lightweight.
Density of the water in which the vessel is ¯oating.
Draft readings port and starboard at the stern, midships and at the bow. Distance from aft perp to Aft draft marks.
Distance from amidships to midship draft marks.
Distance from forward perp to forward draft marks. Distance of LCF from amidships.
Cargo deadweight or `constant', for example, say 10 766 t.
Using above data the Naval Architect will modify the actual draft readings to what they would be at AP, amidships and FP. These values are then used to determine the mean draft at the position of the ship's LCF (see chapter on Trim).
To take into account any Hog or Sag a `mean of means' formula is used. Suppose the drafts at the AP, amidships and FP were 8.994 m, 8.797 m, 8.517 m and LCF was 0.37 m forward of amidships with an LBP of 143.5 m. Then the mean of means draft is: