Webasto exhaust thru hull

GrandWood · Sep 27, 2024

Hello everyone, I’ve installed a webasto diesel heater in our 1972 GB36 classic and am ready to install the exhaust thru hull as the last item on the install.

The thru hull comes with a rubber seal, and a thin metal backing ring. The exhaust will come out just below the deck on the side. I’ve never done a thru hull install, and have done a bit of reading, mostly below the waterline.

I’m wondering if I need to epoxy in a wood backing plate on this install, well above the water line and no valve, I will have a gooseneck at the thru hull to prevent water going down the exhaust. Also do you think I need a sealant like 4200 on the exterior rubber gasket.

Thanks
Joe

tiltrider1 · Sep 27, 2024

You don’t need a backing plate as there is no load on the exhaust tube.

I would seal the exposed core after you cut the hole. This would prevent any water damage if the rubber gasket fails at its job or it you developed an interior leak that happened to find its way to the exhaust tube.

luna · Sep 27, 2024

I'm quite sure that Grand Banks made wood hulls until mid 1973.

If correct, that means your 1972 is a wood hull.

Either glass or wood, a few coats of epoxy on the bore of the new hole would be a smart move.

I don't know what the installation instructions say regarding the hole diameter for this skin fitting but I would be inclined to make it as large as possible while still leaving an adequate edge distance for the exterior fasteners. This creates an air gap between the double walled portion of the exhaust fitting and the hull.
I would also replace the thin interior plate with fender washers and use machine screws c/w nuts, not wood screws for the fasteners. This keeps the hull to fitting air space largely open.

I would not use an adhesive on the gasket. A thin coating (both sides) of pipe dope, Rectorseal No 5 would likely be just fine.

GrandWood · Sep 28, 2024

Thank you guys much appreciated. I have some penetrating epoxy that I will work in around the hole. Yes this is a woody, been using the penetrating epoxy on numerous repairs on the boat, has worked very well.

Also will will go with pipe dope on the rubber gasket, nuts and bolts came with the exhaust.

Gonna be real nice with diesel central heat over electric heaters for sure.

Thanks again

Webasto exhaust thru hull

GrandWood

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tiltrider1

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luna

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GrandWood

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