Quote:
Originally Posted by JamHass
.....I noticed a comment that the two screws/rivets might not be sufficient. I am an engineer, and I'm not concerned. The load will always be static, limited to the climbers weight, and on the order of 10% of the shear strength of 2 1/4-inch screws. I have cleats and other fittings held with 2 1/4 inch bolts threaded into the mast that take far greater loads......Jim
|
Jim,
Obviously you have more installation experience with these than we do, but from the website pictures it really looks like a pair of aluminum pop rivets supporting the mast step.
I did some structural engineering in a past life as well and it wouldn't be the shear loads that would concern me. It would be the tension loads on the fasteners required to react the heel and toe moment cause by the climbers weight. I never really liked having pop rivets in shear, but I would never used them in tension.
And baring detailed dynamic loads, we always assumed a minimum dynamic amplification factor of 2. And I can think of a few scenarios where a factor greater than 1 would occur.
I don't know any actual dimensions but it appears that the width of the mast step is similar to the distance between the rivets and the bottom of the bracket (the heel and toe).
Therefor the loads on the fastener will be similar to the load of someone standing on the edge of the mast step. Add in a dynamic factor, say you slip off the step above and a 200 pound person could applied a tension load of a couple hundred pounds per rivet. And that is a real load for a 1/4 inch aluminum rivet. Nothing like the shear loads they experience holding a cleat to the boom (although I still prefer tapped screws here as well). Blind rivets just weren't designed to take tension.
I don't have a dog in this fight since my sailing priorities would negate mast steps as an option but I think Brion makes some pretty valid points and I would really look hard at any potential failure mechanisms since your life may depend on it.
Bill