Seal bolt holes in wood thwarts/yokes/seats?

I’m replacing a wood seat, thwart, and yoke in a royalex canoe. I’ll need to trim the yoke and thwart to fit, and then drill holes for the bolts. I will definitely seal the freshly trimmed ends with spar varnish. The bolts have the original washers above the gunnel, but are missing washers and nuts below where the wood was, so I may need to find new hardware. Do folks usually try to seal the bolt holes as well, or not worry about them because the washers keep enough moisture out? If sealing bolt holes, do you drill the holes a little bit wider, then dribble varnish down in there and wipe off excess coming out the bottom?

Water will get in anywhere it can and a washer won’t stop it. The undersides of yokes and thwarts are particularly susceptible because that is where the water winds up when you invert the canoe to drain it.

Most all hardware used on canoes is #10 stainless machine screws and matching nuts, either 24 threads per inch pitch (10-24) or 32 tpi pitch (10-32). A number 10 machine screw will require at least an 11/64" diameter hole.

In yokes, thwarts, and seat frames I typically drill the holes two sizes larger which would be 13/64. That allows some wiggle room and some room for finish, whether it be epoxy, varnish, or urethane. Finish is most easily applied inside these holes using a pipe cleaner dipped in the finish.

Very helpful, thanks!

I use 3m…4200 caulk to seal bolt and screws on installation.

Yes your approach sounds perfect, drill the holes slightly large and dribble in varnish…and using pipe cleaners is a great idea, I’m working on a boat today and using Q-tips; pipe cleaners would be better. It’s good to make sure there are stainless steel washers top and bottom to get a better clamp load. My boats are stored inside and have remained bone dry in the seat and thwart holes on my '99 and '96 Bell solos.

Whatever approach you use you want to be able to easily remove wood yokes, thwarts, and seat hangers periodically to refinish (whether it be oil or clear finish) the cut ends and hidden surfaces you can’t get to.

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Thanks all!


Looks like most of the old bolts and top washers are still good, but unfortunately I will have to replace the 6" seat bolts, which were all bent.

Most of the nuts are these four-cornered grabby guys that I don’t think I’ve encountered before - see pics. I see the advantage - they grip the wood so you don’t need to hold the nut with a wrench while tightening the bolt. However, it seems like a major ingress for moisture into the wood, and almost impossible to seal, right?

I’m thinking I’ll replace with flat washers and nuts with nylon insets to help keep them from loosening.

Absolutely use stainless steel nuts with nylon inserts. I don’t know if you have tried recently, but 6" long stainless steel machine screws with a flat Phillips or even slotted heads can be hard to find locally. For some reason, 6" stainless steel carriage bolts are easier to find, but I really hate to use those on canoes.

If you can’t find the appropriate hardware locally, Ed’s Canoe sells a set of four 6" long #10-24 stainless steel flat head machine screws with four countersunk finishing washers, four flat fender washers, and nylon lock nuts:

Those are the same washers that have been onmy old town for almost 50 years. They work fine and don’t loosen.

Use whatever you want, but I wouldn’t reinvent the wheel here

Use a split spring stainless lock washer between your flat fender washer and your nylon lock nut and your hardware will not loosen. The fender washer diffuses the pressure on the underside of your thwart or seat frame and won’t damage the wood.

@pblanc Thanks for the tips and the link to Ed’s. I haven’t gotten to the local hardware store yet but will in the next couple days to see about the 6" bolts - hoping to save ordering online but we’ll see. Old Town also carries the bolts online but they may be out of stock on those along with just about everything else. I might try my local outfitter too - they had the thwart and yoke in stock thankfully.

I understand the fender washers to keep the nuts from biting into the wood, but I’ve never quite understood how the split-spring washers help. I guess they hold tension in the system without having to over-tighten and bite into the wood?

@mike93lx Interesting that those same washer-nuts are on your Old Town as well, I’d assumed they were after-market as much of the outfitting on this boat seems to be. Do yours bite into the wood, as shown by the mark left in the thwart in my pic? If yes, any signs of rot around the nuts, or were they sealed somehow?

Spring washers work as lock washers by exerting a force against the nut that resists it from unscrewing. With the nylon insert nuts you can get by without them but they are inexpensive and unobtrusive so I usually add them.

If you have a situation where you must use a plain stainless hex nut, the split spring washers are pretty essential.

I am sure they are oem. They are used on both seats as well as the thwart.

No rot. The thwart has poly on it but I would be surprised if it was resealed after drilling. Certainly possible though

Interesting, thanks!

I have drilled fairly large holes in wooden boat parts and then filled the hole with epoxy thickened with wood flour. After it cures, I go back and drill the proper sized hole through the epoxy.

I also, almost always us lock washers and wing nuts to bolt seat supports together. Yes, you have to check them every once in a while, but you should anyway.

The advantage is when you have to make an adjustment and are away from your socket set. You can adjust wing nuts by hand.

What adjustment do you need to make to a thwart or seat on the fly?

I really think that all of the options discussed will work just fine.

On this boat I did 5-6 coats of hempseed oil in the holes and on the seat and thwart ends and hidden side of the seat drops, epoxy in the gunwale holes (and then redrilled), stainless flat washers and nylon lock nuts on the bottom and perhaps most important finish washers on top since the original (1999) machine screws had burrowed a good 1/4 inch into the gunwales.Just got it all screwed back together yesterday.

Mike, I like to paddle in the low kneel position. It usually takes me a while to find the exact seat angle that fits me. My knees aren’t what they used to be.