桅杆负荷的计算.pdfVIP

Preliminary Evaluation Of Axial Compression Force On The Mast PRELIMINARY EVALUATION OF AXIAL COMPRESSION FORCE ON THE MAST First of all let’s make a bit of an introduction perhaps useful to clarify the issue ……….. The existing methods for mast and rigging calculation are based on the determination of the maximum compression load acting on the mast being a function of the boat Righting Moment. The ISO guide lines state as follows: …. .”For large sailing multihulls, the righting moment is so huge that it would not be realistic to assess the load on rig by equating heeling and righting moment. Therefore for multihulls, the design heeling moment is taken when the fist reef is taken, as calculated in ISO 12217-3, unless the boat is stated by its manufacturer to be designed to fly a hull …………… ……well…..we will consider it as ….just flying the windward hull !…..…as this situation is most likely to occur on a regular basis on racing multi-hulls and many cruising multi-hulls as well. Figure extracted from Pierre Gutelle, ” The Design of Sailing Yachts”,( International Marine Publishing, first edition, 1979), showing the difference in Rigthing Moment, where, even on small angles of heel, multihulls will face a maximum load much more frequently than a monohull will do. Hence, the main problem encounter with a multihull is that it has a very high Righting Moment if compared with a monohull even at smaller angles of heel and it obviously reaches the maximum as soon as the windward hull rises fully out of the water, as previously stated. This aspect must be considered in the evaluation of a mast compression load. As a result, the dimensions of the mast section has to be considerable larger in respect of the vessel size as well as the wall thickness which has to be a lot thicker on a multihull rather than for a monohull. On the other hand, a multihull, by virtue of its width, has a much