tailieunhanh - Ship Stability for Masters and Mates 5 Episode 6

Tham khảo tài liệu 'ship stability for masters and mates 5 episode 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 164 Ship Stability for Masters and Mates and are given for each one metre difference between 9 metres and the ship s actual KG. To find the correction to the GZ multiply the correction taken from the table for the angle of heel concerned by the difference in KGs. To apply the correction when the ship s KG is greater than 9 metres the ship is less stable and the correction must be subtracted but when the KG is less than 9 metres the ship is more stable and the correction is to be added. Fig. a The derivation of the table is as follows In Figure a KG is 9 m this being the KG for which this set of curves is plotted and GZ represents the righting lever as taken from the curves for this particular angle of heel. Consider the case when the KG is greater than 9 m KG1 in Figure a . The righting lever is reduced to G1Z1. Let G1X be perpendicular to GZ. Then G1Z1 XZ GZ - GX or Corrected GZ Tabulated GZ - Correction Also in triangle GXG1 GX GG1 sin 0 or Correction GG1 sin 0 where 0 is the angle of heel. But GG1 is the difference between 9 m and the ship s actual KG. Therefore the corrections shown in the table on the Cross Curves for each one metre difference of KG are simply the Sines of the angle of heel. Now consider the case where KG is less than 9 m KG2 in Figure b . The length of the righting lever will be increased to G2Z2. Let GY be perpendicular to G2Z2 then G2Z2 YZ2 G2Y Stability and hydrostatic curves 165 but YZ2 GZ therefore G2Z2 GZ G2Y or Corrected GZ Tabulated GZ Correction Also in triangle GG2Y G2Y GG2 sin 0 or Correction GG2 sin heel It will be seen that this is similar to the previous result except that in this case the correction is to be added to the tabulated GZ. Fig. b Example 2 Using the Stability Cross Curves for . Tanker find the GZs at 15-degree intervals between 0 degrees and 90 degrees when the displacement is 38 000 tonnes and the KG is metres. Heel Tabulated GZ KG 9 m Correction GG1 sin 0 Correct GZ KG m 0 0