I wanted to start small with part fabrication so if I screwed up, it wouldn’t be an expensive mistake. My patching got me comfortable enough with the glass and resin to move up to the next step.
The swim platform brackets that came with the boat were heavily corroded and the wrong angle for the transom. The P.O. had shimmed the platform so it would sit level. I made a template of the correct angle before stripping the platform and brackets off the boat. I thought a platform bracket would be a good small lay-up project, and a good break from sanding.
Step one: I made a plug out of wood. I sprayed it with lacquer sanding sealer and sanded it to a smooth finish. Then I waxed it and used sign board to create a flange around the plug that would act as a form for the two part mold.
The plug:
The plug and sign board sprayed with lacquer:
The sign board in place around the plug and the contact surface waxed and sprayed with PVA:
I layed up glass/polyester in both sides of the assembly. When it had cured, I trimmed off the excess on the table saw.
And then removed the sign board strips and popped the two parts of the mold off the plug. I was pretty happy with how it turned out. The reason the two sides are different colors is that I sprayed gelcoat in one side and not the other to see what the difference would be.
The side with the gelcoat had a smoother finish without surface voids. Should have done both sides. Did a little sanding, filling, sanding and was ready to make the first bracket. The layup involved using a layer of mat and two layers of 1808 on each half of the mold before clamping the two halves together. I didn’t think the 1808 would be too happy about making the almost 90 degree angle from the web to the flange of the bracket so I decided to vacuum bag the two sides until the resin kicked and then put them together. This is a dry run without resin to see how it would work.
It’s a lot prettier than the mess I made with resin involved, but in the end it worked out. After I pulled the two halves out of the vacuum, I layed a piece of saturated 1.5 oz mat between them and clamped them together. Then I layed up the flanges all the way around. I used alternating layers of 1.5 oz mat and 18 oz roving, I think it ended up with six layers of each. I wasn’t able to take any pics of the layup, but here’s the mold assembly after it was all clamped together:
And here’s the first part popped from the mold:
And after trimming along with the plug for comparison.
I have no idea how to engineer the scantlings for a part like this, so I took a wag and went with a ¼” web and flanges tapered from 3/8” down to 5/16”. I wanted each bracket to be able to support 350 lbs at the aft end. The only way to see if it would hold up was to do a load test.
I didn’t have enough weight to load it to 350 lbs, so I used a 2x4 bolted to the top of the bracket to extend the moment arm farther out so I could use less weight to apply the same load. The bracket is 24” long. I placed 60 lbs of fertilizer, plus about 20lbs of lead 72” out along the 2x4 to simulate a 240 lb load at the end of the bracket. That was about all the weight the 2x4 looked like it would handle, so I stood on the bracket to get over the 350 lb mark. I couldn’t get the picture I wanted while standing on the bracket, so here’s the partial load test:
I couldn’t see any deflection in the bracket, so I must have made it stiff enough. The fiberglass bracket weighs 3 lb 11 oz, the aluminum bracket is just a hair over 5 lbs. All in all, I’m pleased with how it turned out. Now I need to make three more.
Dave