I’ve been slowly working on restoring an old wooden dinghy in my garage, and I’ve hit a point where I’m just not sure how to proceed with the hull. I used a two-part epoxy to seal the inside, but the outside has these wide, shallow cracks along one plank that I don’t think it can fill. I keep hearing about the traditional method of using cotton caulking and oakum, but honestly, the whole process seems pretty daunting and I’m worried about making it too stiff or, worse, not watertight at all. Has anyone here actually done this on a small boat before?
Yep I have done this on a small dinghy. The outside cracks along a plank are exactly the sort of seam that used to get caulked with cotton and oakum. I did the job years ago after sealing the inside with two part epoxy. The outside still moved with the wood and moisture, so I went with the traditional approach: clean the seam, damp the oakum, stuff it in, and tap it flat with a caulking mallet until it bulges slightly and feels snug. It takes patience because the oakum needs to compress and seal as it swells with moisture. It’s not glamorous and it does slow you down, but it works if you keep the seam lightly tight and then fair the surface and paint. If your hull has wide shallow cracks, that may be your best bet for a long term fix, though it will take time and you’ll want to check leaks over a day or two.
From a practicality angle, I would not dive straight into oakum if you fear stiffness. Modern flexible fillers and slow curing epoxies can keep the hull watertight and allow some movement. The risk with cotton and oakum is you can end up with a brittle stiff seam if you press too hard or overfill. If you want to stay traditional but reduce risk, you can lay a thin patch of fiberglass on the outside and seal over it; but that changes the character.
When I read this I worry the issue may be rot or excessive movement rather than a simple crack. Have you checked for softness or hollow sound behind the plank, or used a moisture meter on the frame? If you misread the seam you could get a leak that grows once the hull flexes in waves.
Maybe the framing here is about the goal not the method. Is the aim to keep it seaworthy while preserving a traditional technique or to finish a project that looks used rather than museum like? The answer might be to do just enough to keep water out without turning the hull into a stiff plank salad. You can keep the interior watertight with epoxy and handle the exterior with a flexible patching compound that echoes the old method.
I get the panic. Sometimes I just step away and draw a quick plan. A small patch, a test seam, then decide. It’s not a race.
One thing I learned is that outside cracks along one plank might be a sign the plank is under more stress than you think. If you want to keep the ship balanced, you may need to temporarily backfill with a flexible filler and then double check the fasteners and the seam. The oakum route is slow but if you want authenticity, treat it like an art project rather than a quick fix.