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Hi again,
First, I very much like the idea of using Spectra instead of nylon, though it is likely that I am simply inclined to use Spectra whenever possible. But in this application, I can see how it could reduce both shock loading and chafe. Stumble, any data on this?
If nylon is used, I would strongly recommend a single- instead of double-braid, as it has far superior energy-absorption properties (see Yale's paper on their Brait product for more on this).
I also agree that a 10:1 SF would be reassuring, but not practicable here, or at least not for every component. Gleb, I understand that the SF's we are discussing might seem high, but 18,000lbs is approximately what the shroud load is, with safety factor, for your boat. If indeed the deck structure and belays cannot support these loads, that level of strength might still be needed.
Bear in mind that it is vanishingly unlikely that your drogue will put a 9-ton stress on the hull, but (a) it could happen, especially in an accelerated load, so it is prudent to design around the possibility, and (b) the safety factor is also there to take some degree of materials degradation and flaws into account. Regarding (a), you ask if it is worth designing a system around a once-in-a-lifetime occurrence. I don't think that is the correct question. You want this drogue precisely because you think that odds are fairly good that you will be in circumstance where reefing or heaving-to will not suffice for survival, but you seem willing to bet that, horrible as the conditions might be, they won't be maximally horrible. I recommend making this system as strong as you can -- or can afford -- and hope that things never get as bad as they could be.
Fair leads,
Brion Toss
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