Replacing Core

[JetStream]

When I took my 1961 Holland-built boat aprt to repair the deck, I found that the core was not even close to today's materials. Apparently, when the boat was built, the deck was constructed by first spraying gel coat, then following with two layers of mat, then a liquid core material was troweled on. This core material is heavy (like 5/8") toward the centerline of the boat and tapers to 0" toward the hull-deck joint. The material is brownish and likely phenol-based with some type of organic filler, perhaps wood flour or something. It has a density of 36 pounds per cubic foot. When you burn it, you can smell the phenol but it does not burn like a urethane.

I found that you can get Part A - Part B, urethane based foam at 30 pounds per cubic foot, specially formulated by Urethane Technology Corp. in Newburgh, NY. They have some minimums of course, but this has compressive strength of about 1000 psi and tensile of about 900 psi. That should suffice for the core and will be almost compatible. The normal pourable urethane foam that is sold everywhere, has a density of about 2 pounds per cubic foot and has poor structural qualities, even though it makes good insulation.

After trowling it in place, I plan to use my router and a couple of guide boards off the existing deck to cut it down to the correct height to replace the top laminate.