Join Date: Jul 2002
Thanked 4 Times in 4 Posts
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My opinion stems from seeing torn aluminum arches and watching cruising couples struggle with what to do as a result. The typical scenario is that an arch is constructed across the full width of the boat's stern, which makes it vulnerable anytime you bring the boat near large physical structures. Cruising boats often find themselves in all kinds of interesting close order drills: small basins, basically immobile dolphins and pilings, uncooperative winds and/or an errant dock line perhaps fouled around the arch. At some point, contact is made and the momentum of a 10+ ton boat is going to be absorbed somehow, which usually means something has to give, and it's going to be the aluminum because nothing else is even remotely as weak. This is a very different dynamic than the static load that you can impart when e.g. pushing/pulling on an arch or climbing up on it to work on the radome or solar panel; in those cases you are feeling the stability of the structure's form. With the maneuvering drills, it's a straight tensile/sheer strength physics experiment - what will give since something must.
Your metal worker, if s/he's concerned about elbows formed from stainless tubing, should know enough to add a gusset in the areas that worry him - essentially, a triangular flat place welded onto the full interior turn of the elbow. Simple, cheap, strong.