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post #190 of Old 01-02-2014
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Re: Do you wear a life jacket?

Originally Posted by pdqaltair View Post
Do we suppose that the force of the wave snapped the tether? That would mean the force of the water on his body was 2000-4000 pounds, equivalent to strapping a 150 hp engine to his butt and blasting him through the water at ridiculous speed. Improbable. The force on his body was probably more in line with a serious wave break, perhaps 500-1000 pounds.

Do we suppose that the impact of his body against the anchor point, without any stretch in the tether, contributed a major part of the force? More probable. Flying across the deck at 8-10 knots could account for all the force.

Sail Delmarva: Dynamic Tethers

A combination? Certainly. However, it seems quite probably that tethers with a little give in them could prevent this sort of breakage. Making them even stronger probably won't help; if the forces on the body are more than 5000 pounds the impact would be fatal.
It seems I did not entirely understood your post. I thought that you were talking about 1000 pounds as the forces that are taken by a tether. If I understand correctly what you mean is that is the force if the tether is completely stretched. If a sailor is projected by the wave on a lose tether then that force can be multiplied several times, therefore the importance of short tethers.

That's more like it?

What I know is that a tether should have a breaking load resistance of about or over 2000 kg

You probably know this old study that revealed some frightening conclusions regarding tethers failures under dynamic charges?

"We were somewhat surprised that there were so many tether failures. 47% of the tethers failed in
such a way as to endanger the wearer. Failures were both in the hardware, stitching, or sometimes both."

Even so on the conclusion they fail to recommend a minimum breaking load under static circumstances, one that could take into consideration dynamic ones.



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