船舶拖带设备结构加强设计

drafter

根据MSC/Circ.884,拖带设备极限强度不低于1.3倍拖索最小破断载荷MBL：
13.10 The ultimate strength of any towline attachment (bracket or bollard and their foundation) should not be less than 1.3 times the minimum breaking load of the towing arrangement which is to be attached.


又根据MSC/Circ.1175，拖带设备设计载荷应为最大拖力（静态系柱拖力BP）的1.25倍
  3.3.1 The design load used for normal towing operations (e.g. harbour/manoeuvring) should be 1.25 times the intended maximum towing load (e.g. static bollard pull) as indicated on the towing and mooring arrangements plan.

再根据MSC/Circ.884,拖索最小破断载荷按下表计算：

12.11 The minimum documented breaking load (MBL) of the main towline should generally be in accordance with the following table:

Bollard pull (BP) (tonnes)	<40	40-90	>90
MBL (tonnes)	3.0xBP	(3.8-BP/50) BP	2.0xBP

假设BP>90T,  则ultimate strength=1.3*2*BP, design load=1.25*BP.
这里面的design load和ultimate strength差距过大，一般拖带设备结构加强设计是选用design load还是ultimate strength进行强度校核的呢？是否有相关的法规解释？

blackmclaren

没毛病，design load和ultimate load是差很多，基本上2倍的关系。强度设计和校验要用design load。