I figured this out years ago when finishing Suilven II, a Wharram Tiki 26 catamaran. We needed a good watertight seal on the forward lockers. These were exposed to the occasional dollop of fast moving “green water” so the seal needed to be good.
Commercially manufactured seals weren’t readily available so I decided to improvise using silicon sealant, molded to the gap between the hatch and the deck coaming. The result was a perfect seal. It was so good that a fall in temperature would lower the pressure in the locker and make the hatch hard to open!
When I finished my Storm LT kayak three years ago I decided to use the same technique to form the fore and aft hatch seals, rather than use a soft rubber seal. It has worked very well, keeping water out during practice wet-exits.
Here’s how to do it.
Clean up and degrease the flange where the hatch will sit. It’s important that the silicon sealant bonds well to this surface.
- Tape of the exterior surfaces where you don’t want extruding silicon to stick.
- Liberally coat the underside and edge of the hatch with a release agent. I used Pathway Polymers “Synlube 531 Release Agent” simply because I already had a can. Whatever release agent you use, I strongly recommend a trial with the silicon rubber you intend to use (GE Tub & Tile 100% silicon in my case). A stick up could be very tricky to undo!
- Squirt a generous bead of silicon onto the flange.
- Carefully place the hatch into the exact position. Push it down to extrude the sealant. You may want to improvise some spacers for exact positioning. It has to right first time!
- Allow the silicon to fully cure then pry off the hatch.
- Trim the surplus silicon with a sharp utility knife.
You now have a durable silicon rubber seal that exactly matches the shape of the hatch. The fit will be so good that you may need a handle or pull cord to remove it.