Trim corrections

The sounding pipe should be positioned at a point within the tank where it will always provided the correct sounding applicable to the sounding tables, regardless of the ship’s trim. However, this position is not always possible to achieve and correction tables for trim should then available to use with the sounding tables. These corrections should be calibrated for every half-meter of trim, by the head and by the stern, over the operational range of trims. Alternatively, sounding tables for different trims may be provided.

d

Sounding pipe

X

Tank Center

If no corrections are available, it may be necessary to calculate them. Appropriate measurements can be taken from the plans of the tank. Correction to soundings (x) = d x trim / LBP where d is distance from the sounding pipe to the tank center.

Sign convention : Trim Sounding forward of tank center Sounding aft of center

Forward Negative (-) Positive (+)

Aft Positive (+) Negative (-)

Not : the accuracy of this formula is acceptable, provided the bottom of the tank is covered with liquid, and the

tank is approximately rectangular.

When a vessel is trimmed a tank may appear full but have a large void space immediately forward of the sounding or ullage point. Alternatively, a tank may have no soundings and appear empty, but still have a considerable quantity of liquid remaining in it.

Liquid slop tanks

Where small quantities of ballast water remain in a ballast hold, on a trimmed ship, this quantity must be included in the assessment. It is possible to calculate the volume of this wedge of liquid, from one sounding, using the wedge formula. The wedge formula was developed in order to determine small volumes of cargo “remaining on board”. The formula assumes a free flowing liquid on an upright, but trimmed vessel, and also it assumes a rectangular tank where the sounding is not constrained by a sounding pipe. The wedge formula is :

Wedge volume = LBP x breadth of tank x (corrected sounding) 2