tailieunhanh - Ship Stability for Masters and Mates 5 Episode 8

Tham khảo tài liệu 'ship stability for masters and mates 5 episode 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 234 Ship Stability for Masters and Mates The draft at the centre of flotation ZF remains unchanged. Let the new draft forward be F and the new draft aft be A so that the trim A F is equal to t . Since no weights have been loaded or discharged the ship s displacement will not have changed and the true mean draft must still be equal to KY. It can be seen from Figure b that the average of the drafts forward and aft is equal to KX the draft amidships. Also ZF KY KX XY or True mean draft Draft amidships correction Referring to Figure b and using the property of similar triangles XY _ t FY L t X FY XY L or Trim X FY Correction FY - Length where FY is the distance of the centre of flotation from amidships. It can also be seen from the figure that when a ship is trimmed by the stern and the centre of flotation is aft of amidships the correction is to be added to the mean of the drafts forward and aft. Also by substituting forward for aft and aft for forward in Figure b it can be seen that the correction is again to be added to the mean of the drafts forward and aft when the ship is trimmed by the head and the centre of flotation is forward of amidships. Fig. c Now consider the ship shown in Figure c which is trimmed by the stern and has the centre of flotation forward of amidships. In this case ZF KY KX XY or True mean draft Draft amidships correction True mean draft 235 The actual correction itself can again be found by using the above formula but in this case the correction is to be subtracted from the mean of the drafts forward and aft. Similarly by substituting forward for aft and aft for forward in this gure it can be seen that the correction is again to be subtracted from the average of the drafts forward and aft when the ship is trimmed by the head and the centre of flotation is aft of amidships. A general rule may now be derived for the application of the correction to the draft amidships in order to find the true mean draft. Rule When the