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Old 02-15-2011, 09:37 PM
Brion Toss Brion Toss is offline
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Join Date: Jun 2005
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Default More variables

Hi again,
And first, note that I started this board as a place to answer questions that were too simple to charge for; you are well past that stage, but this is fun, so I'll go a bit further.
Shock loads are relative to acceleration and elasticity. They can be quantified and included in design load calculations if desired. The short form here is that the materials you are likely to use appropriately are also appropriate for any shock loads, if they are scaled to the design load, times a safety factor. As a counter-example, I've seen main sheets and vangs break gear when owners ill-advisedly replaced Dacron with HM line.
Elasticity can also be quantified, as it is directly related to relative load, and to length. The specific effect of a given level of elasticity is, like all specifics, a bit more involved (he said, retreating behind a veil of mystery). One piece of advice I might offer is to introduce other variables, like cost and durability. Cost/benefit, though sometimes subjective, can be helpful to look at. You might also look at the cut and material your sails are made of, to see if they are consonant with the proposed rope.
25 knots might be right for inshore sailing in some waters and boats, too darn low for others. Remember, this is apparent wind we are talking about, which is relative velocity, a question of boat speed and actual windspeed. So two boats with identical sail areas will have different rig loads, if their hulls can move at different rates in the same actual windspeed. I'd run the numbers at several windspeeds, both to gauge max loads and to calculate things like purchase and winch powers.
Genoa sheet loads are usually higher than mainsheet loads, but it all depends... I can't interpret the rendering of your numbers at this end. Maybe when they show up on email. But then it's a consultation.
Fair leads,
Brion Toss
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