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witzgall 01-03-2008 10:37 PM

plugging up an unused thruhull

I think that I am going to replace the speed and depth transducers on our boat with a single triducer. This means that there will be a hole in the boat that does not need to be there. Once I remove the transducer, what are my options on filling in the hole?


capngregg 01-04-2008 10:17 AM

Re-glassing the area from both outside and inside is the proper way to do it providing your hull is fiberglass. One less hole in the hull to worry about.

Ensure the proper procedures for tapering into the area are observed as well as the lay-up schedule for the fiberglass system you are using. Reapply barrier coat, primer and hull paint as recommended.

If the hull is metal (steel or aluminum) weld in a patch.

Good Luck!

witzgall 01-04-2008 02:26 PM

By tapering, you mean having the cloth end at different points out from the hole, so that they are not on top of one another?

So I start outside, clean prep and lay several size round peices of cloth, alternating direction of weave, and increasing in size.

Then fill the hole form the inside with resin? and perhaps some hole sized pieces of cloth?

Then do the same outside job, but on the inside?

Forgive me, but my fiberglass experience is limited.

I assume I would use epoxy resin and cloth for same?

I assume I end up with a bulge, or is there another way? This is on a solid core Westerly Fulmar.


AjariBonten 01-04-2008 02:32 PM


Originally Posted by witzgall (Post 245440)
Forgive me, but my fiberglass experience is limited.

I would consider having it done professionally. ;)

chucklesR 01-04-2008 02:48 PM

scarf the joint at 12-1, roughed up for a mechanical bond and chemically clean - they follow the same lay up schedule with fiberglass including resin to glass percentage (don't want a hard spot) smooth it back out, inside paint if desired - gelcoat if visable. Outside is same, but fair the hull. Then grind, prep, paint.

If the only thing you understood was grind, prep, paint - hire someone ormake sure you have a PFD on when testing.

sailingdog 01-04-2008 02:58 PM

You're probably better off using epoxy resin, since it will yield a stronger bond in most cases. When thickening the epoxy to fair the exterior, use chopped fiberglass rather than microballons or cabosil (colloidial silica), since the first absorbs water and the second is a bitch to sand.

Omatako 01-04-2008 03:53 PM

I reckon the important thing is to understand that on the outside you don't want a bump but you have to ensure that the plug you are forming with the patch cannot be forced into the boat.

So what you need to do is in an area say twice the size of the hole, grind down till you get a sharp edge at the hole. This results in a "well" that you can fill with glass fibre. That will certainly prevent the "plug" from being forced into the boat and will enable you to fair any bump back to the original level of the hull without compromising the strength of the patch. Then grind the inside to create a decent key for the resin and on this side it doesn't really matter if it stands a little proud.

I'll bow to others on what products you should be using. I would add a pigment to colour the repair the same as the original hull colour.


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