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Old 09-13-2011
CapTim
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There is another consideration here, in terms of shiv load on turning blocks. Regardless of sail size and wind speed, there is a functional limit to how much force can be imparted.

Consider this:

You are sailing with full rig in a hurricane. Good times! Wind speed, lets say, 3000 knots. Why not? In this situation, your turning blocks will be under no more stress than, say, 35 knots of wind.

The boat heels. So, in that hurricane, your boat isn't going to accept all that extra wind force.. it's just going to lay over and take a little rest in the water. So the maximum loads on your turning blocks is not just a function of sail size, but also how much force your boat can exert on the wind to keep itself upright. That force has been called "righting moment" by people much smarter than myself.

I only bring this up to suggest that one can do a lot of math - which we all agree is a ton of fun! - but in the end, it's more of an exercise in mental acrobatics more than sailboat mechanics.

Don't get me wrong.. I do love me some good mental acrobatics. But lets try this.. what type and size rope is your current halyard? Determine the max load on that line, assume it's the max load for your rig (safe assumption, since the halyard hasn't snapped in two on you (I hope)) and double that number. The result is the size of turning block you need.

I know it's not sexy.. but it'll get you on the water, if that's where you want to be

... or I'm wrong.

Living aboard, currently in the Chesapeake
O'Day 37, still new to us
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