Page 447 - statbility for masters and mates

Draft Surveys 435
Means of means draft dAP 6 dAM dFP =8
8:994 6 8:797 8:517 =8
Thus, mean of means draft 8:787 m
When corrected for LCF position, the mean draft is 8.786 m:
The Naval Architect uses this draft of 8.786 m on the ship's Hydrostatic Curves or tabulated data to obtain a ®rst estimate of the displacement and TPC. These are of course for salt water density of 1.025 t/m3. Assume this displacement was 17 622 t and the TPC was 25.86 t. The Naval Architect can now evaluate the Fresh Water Allowance and proceed to make a
correction for density.
FWA W= 4 TPC 17 662= 4 25:86
FWA 171 mm
The density correction is then made (see chapter on Density correction). Assume the water was of 1.019t/m3. Consequently this correction would be minus 0.041 m.
Thus, the final true draft would be 8.786 0:041 8.745 m:
Interpolating once more the Hydrostatic data the ®nal Displacement at the time of the Draft Survey is obtained. Pressume this ®nal Displacement is 17 537 tonnes.
From this ®gure must be deducted the Lightweight and all other deadweight items (except the `constant' or Cargo deadweight). Assume this Lightweight was 5675 t and the residual dwt of oil, fresh water, stores, crew and effects, water ballast etc. was 1112t. This residual dwt would have been estimated after all tanks had been sounded and all compartments been checked for contents. Then the ®nal Cargo dwt or `constant' is:
Cargo deadweight 17 537 5675 1112 10 750 tonnes
This compares favourably with the Cargo dwt given at the port of departure, that is 10 766 tonnes, a difference of 0.15 per cent. In a perfect world the Cargo dwt at the arrival port would have been `constant' at 10766t. However, ships are not built to this degree of accuracy and measurement to this standard is very hard to achieve.
Summary:
Corrections have been made for:
Draft mark positions. Hog or sag.
True mean draft is 8.745 m
Cargo deadweight or `constant' is 10 750 t 0:15 per cent
Trim and LCF position. Density of water.
True displacement is 17 537 t