A Study On The Safety Of Deep-Water Weighing Anchor Of Ships

With the development of international shipping trade,the tendency of large-size ships is becoming increasingly apparent.As a result,the anchorage waters are planned to expand out of the harbor limit and the depth of newly large harbors gradually increasing.When ships weigh anchor from deep-water anchorages,various accidents such as anchor lost,chain scission and other damages caused by different factors happen frequently.On account of this,this paper is written to study this proplem through theoretical analysis and field experiment,which is of some reference value for ship weighing anchor.Firstly,four external loads when ships weighing anchor have been analyzed in this paper,include the ground-breaking resistance force of anchor lifting,weight of anchor chain,force of friction between anchor chain and hawse pipe,then discussed the parameters and working performance of the windlass under regulations of the classification society,which is used to get a preliminary acquaintance of the safety when ships weighing anchor.Then,the ground-breaking resistance force of four different kinds of anchors(AC-14 anchor,DA-1 anchor,Pool anchor and Speck anchor)have been experimented on the fine sand and mud bottom,respectively to study the demanded pulling force of the windlass with varied holding power when weighing anchor and the influence on the pulling force by changing the weighing anchor angle with the holding power fixed.By drawing the real-time curve of the pulling out force with SH-TEST and analyzing it according to the current norms of anchor gears of CCS,compare the processing result with the ratios(a dimensionless number)including the loads of windlass,the weight of anchor chains,the ground-breaking force to get a algorithm model to calculate the limiting water depth for weighing anchor safely.In this model,the weighing anchor performance,ground-breaking resistance force of anchor lifting,weight of the anchor chain,force of friction between anchor chain and the hawse pipe and other factors are all taken into consideration.It can be predicted with the help of the result that whether the deep-water moored vessel can weigh anchor safely by analyzing the current meteorological condition,sea state and the ship itself.There are two methods introduced in the essay to weigh anchor with the help of the chain cable compressor or brake band in emergency with both advantages and disadvantages analyzed by comparing them.If the weighing anchor force is insufficient,these methods can help improve the safety of deep-water weighing anchor to some extent.At the end of this paper,many factors that may cause damages to the windlass as a result of overloading,such as bad sea state,the vessel age and poor maintaining,as well as the solutions are further discussed.This study is of much reference value for the ships to weigh anchor in deep sea safely.