Prisim light

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May 4, 2023
Vessel Name
Vessel Make
Pacific Trawler 37
Owner of 37’ Pacific trawler
The prisim light over my head keeps leaking
Had it out and re caulked and the next rain day it leaked again!
Driving me nuts
Anyone else have this issue?
Maybe the leak is somewhere else but shows up on the prism.
I've found drips 2 decks lower and 40' away from their entry point.
What caulk did you use? Some caulks don’t play well with glass or plastic. Also as said above the leak could be coming from a long way away.
It was a Sika caulk - black I forget the number.
I’m removing it again and going to redo.
Any caulk suggestions I’m open too.

Hopefully it’s not coming in from elsewhere.

Hi Chris on SeaLink.

Regarding the prism leak, where is it located? Some overheads are balsa core which requires a different repair (and discovery of where the water is getting in).

Is SeaLink the previous BLUE GOOSE?

Let me know with a message, and I'll add you to the Pacific Trawler Owner's List.

Cheers, Jay N
Prisim leak

Maybe balsa wood core not really sure.
When I get back to the vessel I’m removing it and trying again.
I’m wondering if someone new what caulk to use?

That’s correct. Previously the blue goose.
When I rebedded my deck prisms I’m pretty sure I used 4000uv. Might have been 4200, can’t remember exactly. But they’re holding great. I did an epoxy seal on the edges of the holes while I had them out too.
I prefer silpruf. My friend Rich has decades of sailing experience. He said SilPruf will flex with the boat and keep things watertight. I was having hatch issues. It worked for me.


Caveat: I'm in Florida without deep freezes. I do not know how it functions in the north.

I replaced uv4000 with silpruf. Please note silpruf has a shelf life so buying where you can get a fresh tube is a good idea.
Prism Leak

Maybe balsa wood core not really sure.
When I get back to the vessel I’m removing it and trying again.
I’m wondering if someone new what caulk to use?

I'm not aware of the builder of your boat installing prisms to help provide more light in the head. It is probable that it was added by a previous owner.

In any event, it is very likely that the boat deck was constructed with a cored structure. A proper installation should include thickened epoxy to form an internal block within the core around the prism opening (as Bmarler indicated in post #7 above).

Without the block, the prism will leak from any water source penetrating the boat deck. Typically, water can get in from the aft pilothouse window, fastenings holding the stack in place, and the possibility of the pilothouse/boat deck seam.

There are some good caulk suggestions, but most will work fine if the core is dry and secure.

If you have a chance, post a picture of the prism.
Last edited:
Rod Collins has an excellent article on caulking.
Great thanks for the info
I think I’ll try it.
I’m in Florida also. Or at least the vessel is.
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