tailieunhanh - Ship Hydrostatics and Stability 2010 Part 4

Tham khảo tài liệu 'ship hydrostatics and stability 2010 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Basic ship hydrostatics 65 8 2 111 a 1 38 2 I Figure Monohull versus catamaran We can obtain the same displacement volume with two hulls of breadth B 2 the same length L and the same draught T. Assuming that the distance between the centrelines of the two hulls is 3B 2 the resulting metacentric radius is 12 2L V 2 J 19B2 48T The first term between parantheses represents the sum of the moments of inertia of the waterlines about their own centrelines. The second term accounts for the parallel translation of the hulls from the plane of symmetry of the catamaran. The second term is visibly the greater. The ratio of the catamaran BM to that of the monohul is The improvement in stability is remarkable. Catamarans offer also the advantage of larger deck areas and under certain conditions improved hydrodynamic performances. On the other hand the weight of structures increases and the overall performance in waves must be carefully checked. It may be worth mentioning that also many vessels with three hulls that is trimarans have been built. Moreover a company in Southampton developed a remarkable concept of a large ship with a main slender hull and four side hulls that is a pentamaran. Example - Submerged bodies Submerged bodies have no waterplane therefore their metacentric radii are equal to zero. Then the condition of initial stability is reduced to GM KB - KG 0 In simple words the centre of gravity G must be situated under the centre of buoyancy B. We invite the reader to draw a sketch showing the two mentioned points and derive the condition of stability by simple mechanical considerations. Submerged bodies do not develop hydrostatic moments that oppose inclinations as they do not develop hydrostatic forces that oppose changes of depth. 66 Ship Hydrostatics and Stability Example - An offshore platform Figure is a sketch of an offshore platform of the semi-submersible type. The buoyancy is provided by four pontoons each of diameter b and length f. The .