Builders - Modifications 

Replacing Net Rails

by Scott McCulley

Engineers love failure. At least that's what my materials professor taught us in college. We learn more from a bridge that falls down than from one that stands the test of time. Or so I told myself as I extracted a piece of broken rail from my trousers after putting my foot through the port net.

The Tramp is a fairly solidly built boat, with the possible exception of the inboard rails supporting the nets between the main hull and amas. Haines Hunter drilled holes in a 9' section of 1/2" aluminum bar stock and pop-riveted it into a channel on the hull. Cut-outs in the hull allow the lashing for the nets to pass through. Unfortunately, the lifespan of an aluminum pop-rivet placed under shear stress is less than the age of my boat. When one rivet gives up the ghost that sets off a chain reaction, shearing additional pop-rivets until the rail breaks. I wanted to rebuild stronger than the original.

I examined my neighbor's F-24, which uses a mushroom anchor bolted through the deck edge. It was not possible to emulate with the Tramp's deck line. I talked with some other multi-hull owners at NWMHA and got several good suggestions for designing a stronger rail. One that sounded good was to fiberglass a plastic tube into the old channel and slide a rod through. It also sounded like a lot of work and would be difficult to match the faded yellow gelcoat. Without fiberglass, the plastic tube would be susceptible to UV and might not be strong enough. I decided to use an aluminum tube with pop-rivets and marine adhesive to get the same benefit with less work.

Demolition was easy. I drilled out the old pop-rivets and pulled the remainder of the old rail off. A razor blade peeled off the old silicon sealant. Then I lightly sanded to rough up the gelcoat to accept adhesive and cleaned with acetone.

I bought two 12' sections of 1/2" aluminum rod and a 10' section of 1/2" inside diameter aluminum tubing from Alaskan Copper in Seattle. The aluminum tubing was hacksawed to create brackets that fit between the hull cutouts. A 45 degree angle was used on all cuts to allow working space for the drill and pop-rivet gun. This allowed me to double the number of pop-rivets used to secure the rail without weakening the aluminum rod.

	The finished bracket was used to mark new holes to be drilled in the boat. After drilling, marine adhesive was applied to the bottom of the bracket and then it was fixed in place with two pop-rivets. The marine adhesive will take most of the load on the bracket after it cures and seal the holes in the fiberglass.
	The aluminum rod was tapped into the brackets with a hammer and marked for length. One quick cut to fit. Round off the ends with a file for a more finished look. The last step was to lash the new nets on and get ready to launch!

Last updated 11 Apr 2000

Editor: Don't miss Scott's Tramp/Eagle Website for more great information on Tramp trimarans.