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Screws have stripped backing block for rudder

wjejr

Active Member
Hello fellow Sunfishers,

The screws on that hold the bronze plate won't fully tighten, and it seems that over the years water has gotten into the holes and weakened/rotted the wood fibers. The block seems tight to the hull as I can push on the screws and nothing seems to move. Obviously don't want to push too hard. :) I can think of a couple of options:

1. Drill the holes out carefully to a slightly larger size, and then fill the holes with epoxy mixed with wood flour. I would do this with the boat upside down so the drill shavings fall out and, after filling the holes with thickened epoxy, tape over the holes so that the epoxy would not run out, or

2. Drill out holes to 3/8" and then epoxy in mahogany wood bungs.

In both cases, I would then re-drill with for the wood screws.

Let me know what you think, or if there are other options. At this point I'm not particularly keen about putting in an inspection port in the stern as the boat does not seem particularly heavy.

Thanks in advance for any help and insights.
 

kmac17

New Member
Option 3... a variation on 1 & 2. Bury nuts in epoxy filled with silica, wood flour or similar (high density is better than light weight in this case) and use machine screws instead of wood screws. I used this technique to mount a plate to the top of a keel on my i550. It was provided to me by tech support at West Systems and has been rock solid since day 1.

Supplies,
a. Stainless screws or bolts of the proper size with 2 regular nuts each.
b. epoxy resin and hardener. Use UV stable hardener if possible (west 207 fits this bill)
c. silica, wood flour or similar filler. High density is better then fairing type fillers.
(note b. and c. can be replaced by west systems six/10 or similar. Would be perfect for this type of job if you don't want to mess with all or already have resin, hardener and filler)
d. clear packing tape (polyethylene will not bond to epoxy, packing tape is polyethylene, thin and cheap works great).
e. McLube or similar spray silicone wax. This is your release agent.

Process,
a. Drill holes large enough for the nuts, rough inside is good and as deep as your screws/bolts. Blocks is probably 1" thick give or take. If you don't drill all the way through, you can do this right side up. Current screws should give you an idea of how much room you have to work with. 4x the width of the screw should be enough for this to work well. It's ok, almost preferred, if the bottom of the hole is wider than the top too.
b. CRITICAL Spray the screws with McLube or similar silicone spray wax/release agent. Don't spay the nuts.
c. Cover area and back of the fitting or template with clear packing tape. Epoxy won't bond to the tape, so cover everything but the holes.
d. Mix up some thickened epoxy to peanut butter consistency and fill the holes.
e. Embed bolts with nuts spaced apart ¼" or so. They (the bolts) should be through your fitting or template so it (the fitting) can hold them in alignment while the epoxy sets.
(you could make a template to hold the bolts in alignment, just make sure that the template is thiner than your fitting so the finished hole is deep enough.)
f. tape the fitting or template in place so it's correctly positioned.
g. allow epoxy to cure.
h. Crack the bolts loose, it will take some effort but they will come loose. You now have threaded holes that fit your plate perfectly and will last just about forever.
i. Remove packing tape, clean up as needed which should not be much.
j. mount fitting with a little 4200 or silicone, let cure. (insurance and protects againts dissimilar metals, your threaded holes won't leak).
k. go sailing.

You can try it in any old block of wood to experiment. Should only take 10 minutes to set it up and try it.

Why not option 1? I've had bad luck threading wood screws into thickened epoxy over time. The first time they are fine, then the second time one of them will strip out. Pretty soon you are back to where you started. And this is your rudder which sees lots of load when things get interesting. The embedded stainless steel nut will not have that problem.

Why not option 2? I like 2 better than 1 but it is work to get the plugs to fit well and be flush with the deck. Probably finishing or refinishing issues. You can make smaller holes for the nuts and get a stronger result in my opinion.

Good luck and Cheers, Kevin.
 

wjejr

Active Member
Hi Kevin,

That seems like a good idea. Thank you.

Any reason for stainless rather than bronze?

Thanks again, Jim
 

kmac17

New Member
Jim,

Technically, I think both metals would work fine for this process. I have personal experience with stainless. It's a harder alloy then bronze. It has also generally replaced bronze as a go to corrosion resistant metal in most things boat, in particular 18-8 or 316 stainless for nuts and bolts. I'm also much more comfortable with stainless because it's what I've used in my other much larger project. If you are sailing in salt water than you probably want to be more careful with mixing metals because the sea salt adds additional elements to the mix that can catalyze corrosion.

Kevin.
 
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