[Public-List] Dynamic Loads while sailing

[Jim Davis]

>From L. Francis Herreshoff's "The Common Sense of Yacht Design, Vol 1"  page 114.
This indicates there could be a loading in excess of five tons on the deck of an A30.
Just something more for the thought process.

I apologies for the poor OCR.

Jim Davis
S/V Isa Lei
CT 35

But our sail is not flat, so that more likely the strains are about as shown in Figure 151,  and in this diagram the total length of the lines added together would equal the pull downward of the mainsheet so that we see the strain are mostly near the masthead and after end of boom. If the strains of the mainsail are rather concentrated aloft, the strains of the  jib or headsail are all concentrated in one spot, and if the forestay 
pulls forward as much as the mainsail pulls aft then we have an enormous  strain in one spot; and as a matter of fact, when the backstays are carried  unnecessarily tight the strain at this point is more than most people realize .  So the fore and aft strains on the mast are the pull of the mainsheet and backstay  which has to be counteracted by the pull of the forestay. These strains may be about as follows (in strong breezes) as compared to the weight or displacement of the yacht;  mainsheet 12 per cent, backstay 13 per cent, forestay 25 per cent, depending on the angle of pull. While the side strains on the mast are not as 

great as the fore and aft strains, still as the shrouds do not have as favorable  leads the strain on the shrouds is great, particularly on narrow yachts or where the shrouds' are carried inboard to clear a lappiiig jib. At times this shroud strain is as much as 100 percent of the yacht's weight, so that with the halyards and headsail sheets pulling downward the mast must at times  take a compression strain of over 150 per cent of the yacht's weight. 



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