Factors of safety

An article from AES

Factors of Safety on rigging vary greatly from design office to design office and there must also be variance on the type of vessel itself. As commentary on our industry here are some good rules of thumb. Forestay 2.0/2.5. Verticals 2.25/2.75 and Cap Shroud 2.75/3.0. The D1's vary between 2.75/3.5 and other D's 2.5/3.5 One issue is that whilst many designers are using RM30 the righting moment at 30 degrees as a basis for maximum safe angle of heel and therefore maximum safe working loads, current practise varies widely on analysis under reefing and if reefed loads are not applied to the D's individually, then it transpires that much heavier D's are needed or that higher Factors of safety are required. There are a lot of yachts that do not reef at all (race yachts) but if they have a delivery mainsail of cut down dimensions then it is important that these sails do not overload the adjacent D. Otherwise a safe move can turn around and bite you. Worst of all some designers are keen to compare factors of safety but use RM20 or RM25 so the factors do not really get a fair comparison. Clearly some yachts would dip their gunwhales under and actually sink at 30 degrees of heel, so care is needed before setting factors of safety or the basis on which these factors might be applied.