Mounting new thru-hulls; to bead or not to bead?

[FrankyB]

I'm in the process of restoring a 1989 Four Winns 315 Vista, just painted the hull and wanting to replace all the brittle sun beat thru-hulls with SS ones. The hull is now dark navy blue and I'm hoping the SS thru hulls will help bring some "sizzle." My challenge: as my picture shows, there is a rubber washer with the unit that came with no instructions. Does the washer go on the exterior of the hull or inside the hull. I've bounced this across West Marine tech support and Atwood tech support and received differing advise. WM advised to use a bead of 4200 under the mushroom and to use the rubber washer behind the nut on the interior of the hull. A female engineer from Atwood stated the rubber should go on the exterior of the hull and no adhesive or silicone is needed, just tighten the nut on the interior. What have others done?

​Frank

 

[dingbat]

Rubber gaskets have no place in a marine application. They take a compression set and are highly susceptible to chemical and uv attack. Throw the rubber washer as far as you can and install with 3m 4200. Make sure to double clamp all hose connections

 

[Scott Danforth]

+1^ what he said.