How much force will epoxied hardware take ?

[Bob Early]

My boat ( Hunter 27 '1978) has several hardware issue, involving screws and bolts. I am very new to this type of fiberglass and epoxy, but cautiously enthusiastic. After reading the section “Installing Hardware” in the West System 002-550, I still have questions.I want to mount overhead grab rails (probably teak with multiple holds), but am unclear as to how much weight the hardware will hold with the epoxy base. It seems like the core is about an inch thick (It’d be nice to have a non-invasive means of measuring the thickness before drilling the holes.)Would the “wetted sponge” idea work better in this case? Additionally I’d like to add a couple of mid hull cleats, but the interior seems completely inaccessible without a major project. Is there a reasonable way to make the holes in the side decks, secure the mounting bolts with epoxy and maintain strength? (I have seen those “pop up” cleats and they seem like they would be good for this application, but require about 2 inches of space and of course, secure mounting.I realize your answering questions about using West System products, but whenever I want to mount some hardware or add stuff to the boats fiberglass, I always find my self asking the question: How much non-static force will this fiberglass take, before I need to concern myself with failure and possible serious damage? Is there a reasonable method of determining the strength or force that, for example, the foredeck can take by adding more hardware to it?Thanks,Bob Early

 

[Bruce Niederer]

Hardware Bonding

I can't give you any specific values for the strength increase of hardware mounted using our recommended hardware bonding technique but I do have a good story as anecdotal evidence to it's effectiveness. A local Bay City boat builder, Jon Staudaker, built some of the most well known unlimited class hydroplanes out of plywood and WEST SYSTEM epoxy in the 60's and 70's. These boats were powered with extremely high HP engines and generated huge amounts of torque, which would pull the motor mounts loose after each race. Jon was instrumental in the developement of our technique. To address the problem with the motor mounts, he drilled oversized holes where the mounts were attached to the wood stringers. The holes were the diameter of the outside point of a threaded rod connector that fit the bolts being mounted. The outside of the connectors were roughed up with sand paper and a bit of mold release put on the threads of the bolt. He then wet out the holes with neat (unfilled) epoxy to allow it to wick into the grain, then added some 404 High Density filler to his mixed epoxy to create a mayonnaise consistency putty, filled the holes with this putty about 1/2 full, inserted the connector with the bolt in so that the filled epoxy squeezed out the top of the hole, removed the excess and allowed it to cure. Once cured, he removed the bolt and mounted the engine. The resulting strength of the epoxy mounted hardware not only solved the problem of the engine torque pulling the mounts out, but it was so strong that they tapped a hole in the engine block, installed an eye bolt, and hauled the boats out of the water by the single eye bolt! I tell you this to illustrate that for your application, bonding in the hand rails or deck cleats will make it so strong that the laminate will fail before the mounted hardware does. Since you have the Fiberglass Boat repair manual I suggest you use the technique described that uses a nut in the same manner as Jon used the connectors to put you hardware in. Put the nut on the bottom of the bolt so it sits completely in the hole at the bottom. You can use regular PAM® cooking spray to coat the threads of the bolts. Working overhead means you'll have to fill the epoxy to a non-sag consistency, inject or work it into the hole about half full, insert the assembly and allow it to cure. The bolt will come right out and you can then install the rails or cleats.Your final question about the strength of your hull and/or deck laminate is something I can't answer. Hunter's are fairly well built boats and I can't imagine that adding a cleat, particularly one mounted as I described, would strain the laminate strength much.