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Old 07-24-2012
Stumble Stumble is offline
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Re: Pad eyes for tethers and jacklines

John,

The goal is to spread a torque load out over a larger surface area. With a pad eye, the torque loads are spread both on the front face, and from the backing plate, over a larger surface area, while a U bolt can only spread them from the back. This could lead to a systems failure where the backing plate (farthest from the direction of pull) applies force in a very small area, and the front applies it in an even smaller one.

Think of it like a see-saw. One edge is trying to push into the boat, the other is trying to pull out of the deck. A backing plate only works on one side of the interface .


The real risk of course is not a broken section of the boat, but that general working over time could fracture the hull laminate. Likely below the surface, or below the backing plate. This could lead to a catastrophic failure of the system when it is put under the type of loads generated by someone falling overboard. Of course this is to some extent dependent on the thickness of the hull section it is bonded into.

For the OP on an Olson 30, the laminate where he is talking about is either 1 or 2 layers thick, and that's it. I actually own an Olson 30 and know exacally where he is talking about. So for this installation I think the risk is much higher, than if you were talking about a high strength area where there is a lot of deck thickness to help absorb these loads.


As to value, To me anything that I am going to absolutely have to trust my life too better be the best possible option. There may be places where a U bolt would work fine (places where the load path is more predictable) but in life saving gear, I want it absolutely right.


TJ also raised an issue that I missed. With no flange to bed down, a U-bolt would be more difficult to waterproof. It can be done, by drilling out the core from the back side, filling the larger holes, then replacing this with epoxy. Then redrilling the mounting holes strait through the epoxy. This is the proper way to seal core anywhere you have a core penetration anyway, but then you are relying on just the goo at the backing plate to keep water out. Particularly in a verticle installation there will be standing water in the bolt holes. Which is almost begging for stainless crevice corrosion.
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