Reuse through-hull hole, but fill two old bolt holes

[mikebikeboy]

I have removed an old Spartan Marine seacock and through hull that were damaged. I want to replace this seacock with a Groco, with the backing plate that you don't have to bolt through the hull.

I will reuse the through-hull hole, however there are the two bolt holes on either side that I will no longer need. For filling them, being in close proximity to the larger hole, I am reluctant to grind them down for glassing. Is there another way to fill these holes that is acceptable? They are small, maybe 1/4 inch in diameter, plus the countersink bevel which widens them a bit on the outside.

Thank you.

[WSMFP]

I would fill with this and then sand.

https://www.westsystem.com/specialty...poxy-adhesive/

[Cheechako]

I think you can just fill them. Kitty Hair would be nice as it has glass filler in it. But if not very big you could just epoxy with filler.

[SVTatia]

Originally Posted by mikebikeboy

I have removed an old Spartan Marine seacock and through hull that were damaged. I want to replace this seacock with a Groco, with the backing plate that you don't have to bolt through the hull.

I will reuse the through-hull hole, however there are the two bolt holes on either side that I will no longer need. For filling them, being in close proximity to the larger hole, I am reluctant to grind them down for glassing. Is there another way to fill these holes that is acceptable? They are small, maybe 1/4 inch in diameter, plus the countersink bevel which widens them a bit on the outside.

Thank you.

• Drill the existing holes with a slightly larger bit to "clean" them and expose good glass.
• Make a small bevel with a countersink bit inside and outside
• Tape the outside hole with duck tape
• Fill with epoxy mixed with cabosil, semi-liquid from the inside, slowly to avoid air pockets.
• Next day remove the tape.

[Dsanduril]

I too would fill with a thickened epoxy. I use WEST a lot, but there are other options if that is not easily available.

I would also add a new countersink bevel on the inside - doesn't have to be large, but that way the filler has a narrow neck (the center of the hole) and a larger surface on both the inside and the outside (an hourglass shape). This will help prevent the plug from popping out if it gets hit. Don't know what the inside looks like, but if it is flat enough would also use the epoxy to put a layer or two of glass over the whole area. Can't hurt, easy enough to cut the hole for the throughull, reinforces (a little) the throughull area and the plugs.

That's a belt and suspenders approach, the plugs by themselves should be just fine, but I'm the cautious type below the waterline.

[SVTatia]

Originally Posted by mikebikeboy

I have removed an old Spartan Marine seacock and through hull that were damaged. I want to replace this seacock with a Groco, with the backing plate that you don't have to bolt through the hull.
....

I guess you will be using Maine Sail's method?

https://pbase.com/mainecruising/backing_blocks

[mikebikeboy]

Dern it, I really like this forum! Thanks guys!

I like the idea of the hourglass plug using thickened epoxy mixed with kitty hair, and glassing over on the inside of the hull for a little extra strength.

Yes, that's the backing block method I was planning on, from the Marine How To article. But I was going to buy the backing plate from Groco, however I am not familiar with the "marine PVC foam" they use for this product. Has anyone had any experience with that material? Here is the link to that product.

https://www.groco.net/products/valve...ng-blocks/bb-1

Many thanks.

[HopCar]

The double countersink and fill with thickened epoxy sounds good but I wouldn’t worry too much about it. Don’t forget the backing plate will cover those holes.

[SVTatia]

Originally Posted by mikebikeboy

Dern it, I really like this forum! Thanks guys!

I like the idea of the hourglass plug using thickened epoxy mixed with kitty hair, and glassing over on the inside of the hull for a little extra strength.

Yes, that's the backing block method I was planning on, from the Marine How To article. But I was going to buy the backing plate from Groco, however I am not familiar with the "marine PVC foam" they use for this product. Has anyone had any experience with that material? Here is the link to that product.

https://www.groco.net/products/valve...ng-blocks/bb-1

Many thanks.

I wanted the backing plates to be a bit bigger than the ones supplied by Spartan and I am not sure wthat material they use but they are pricey! I had 3 seacocks to do.
I ended up buying a 12/24 piece of 1/2" GPO3 from McMaster Carr, cut it with a hole saw and drilled the holes.

https://www.mcmaster.com/standard-plastic-sheets

[Jetx]

Originally Posted by mikebikeboy

I was going to buy the backing plate from Groco, however I am not familiar with the "marine PVC foam" they use for this product. Has anyone had any experience with that material?

Groco makes quality hardware, so their backing plates are probably fine. That said, I didn’t like the sound of PVC foam or the brass inserts they use, so I bought solid fiberglass plates from dreamgreen instead. They’re stronger than the hull, and all fit perfectly, so very happy with how they turned out.

[mikebikeboy]

Thanks to all for the comments, I really appreciate this.

I suppose laying a layer of glass on the inside of the holes is not necessary since the backing plate will be covering those holes

Jetx---Thanks! Cheaper, and better material than the Groco ones. I'll probably order me up one.

[bcboomer]

Take a look at Trudesign seacocks. Epoxy them in and they become a maintenance free part of the hull.

[deblen]

https://marinehowto.com/seacock-thru-hull-primer/


https://marinehowto.com/replacing-th...-and-seacocks/

[Cadence]

You mentioned a backing plate. It should extend over those holes so just fill them from the outside. Take the suggestion of reaming them out before placing the backing plate just so your not trying to fill against an old adhesive.

[Dsanduril]

Just because the internet is a good place to be contrary

IF the backing plate covers the holes, and IF you are using MaineSail's method of gluing down the backing block then I'd prepare the holes (ream and chamfer inside) and then just glue down the backing block. Let the filler/glue for the backing block fill the holes, trowel smooth on the outside. That get's it done in one go, doesn't have any secondary bonds, and does away with smaller fill blocks.