Filling/Fairing Screw Heads Below the Waterline

[Finding Cloud]

I recently had some old bronze through hulls replaced with Marelon by my local yard. They screwed all the way through the hull which I was not expecting. I was frustrated because the whole point of moving to Marelon was to reduce underwater metals, but after doing some research I've learned this is an acceptable method for securing through hulls and that they can be faired over. I'm at the top of my budget with them, so I'd like to now fill and fair them myself before applying new bottom paint and splashing. The screws are countersunk, but not very deep. Would love to know the best method and materials to use to finish off this job of hiding these screws.

Also - I am not looking for opinions on Marelon vs. Bronze! I've done extensive research and I trust it!

[Dave852]

Gosh, I would not be happy with that. I would go so far as to make a donut of biaxiel glass and make screws go away. If you use filler make sure there is no way it could flake off exposing what looks like SS screws to the water.

[roverhi]

Fill with a sandable caulk and sand fair. Someone's going to want to get at those fasteners in the future and will be cursing you if the slot/phillips is filled with epoxy/hardened filler.

[slug]

Originally Posted by Finding Cloud

I recently had some old bronze through hulls replaced with Marelon by my local yard. They screwed all the way through the hull which I was not expecting. I was frustrated because the whole point of moving to Marelon was to reduce underwater metals, but after doing some research I've learned this is an acceptable method for securing through hulls and that they can be faired over. I'm at the top of my budget with them, so I'd like to now fill and fair them myself before applying new bottom paint and splashing. The screws are countersunk, but not very deep. Would love to know the best method and materials to use to finish off this job of hiding these screws.



Also - I am not looking for opinions on Marelon vs. Bronze! I've done extensive research and I trust it!

Call the shipyard and have them remove the valve , plug the holes with epoxy , then re install it correctly

You do not thru bolt the valve onto the hull

The valve is threaded onto the thru hull fitting , then three wood screws are inserted from the inside and into the backing block to fix the valve location
No thru bolts
The fasteners only prevent the valve from rotating on the thru hull fitting

The people who installed that marlon valve can’t read instructions

[rslifkin]

Technically bolting through the hull or bolting into a well-attached backing plate are both considered acceptable. Personally I prefer bolts into the backing plate, as it means less holes in the boat. Bolts through the hull are the more old-school way of doing it, however.

[Orion Jim]

Another example of putting your complete trust in a “professional”. Any work done by a “professional” must be thoroughly vetted beforehand. We all have to do our homework and ensure the complete task is described in the work order/contract along with final results and remedies should the provider not perform the task as described. If you’re not up to the task then hire a surveyor to ensure your best interests are preserved and ABYC standards are met.
Too often there is the right way and the easy way...they charge the same for both.

[captlloyd]

Originally Posted by roverhi

Fill with a sandable caulk and sand fair. Someone's going to want to get at those fasteners in the future and will be cursing you if the slot/phillips is filled with epoxy/hardened filler.

Agreed. Not a major issue.

[jimbunyard]

Depending on the type of stainless, the installation is finished; don't fill or cover them with anything, technically even bottom paint, as there is a real risk of crevice corrosion.

If you want to fill the recesses, remove the screws and replace them with properly-bedded silicone-bronze fasteners.

[stormalong]

Make the unprofessional professionals replace the stainless screws with bronze. Underwater is no place for stainless unless it is an Aquamet 22 prop shaft.

[Ramona]

Just use a bit of body filler to cover the slots in the screws. Will be easy to dig out later if needed. I used SS self tappers to secure fibreglass vents on the hull of my commercial fishing vessel for about 25 years. The planks were Oregon. Each year when I pulled out the screws to paint under the fittings the screws were always immaculate.

[Jim Cate]

I won't comment on whether the installation is skookum or not, but it you want to fill and fair, put some wax into the Phillips head grooves before bogging. This will make getting the screws out someday a bit easier: no bog in the grooves!

Jim

[Wotname]

Originally Posted by Jim Cate

I won't comment on whether the installation is skookum or not, but it you want to fill and fair, put some wax into the Phillips head grooves before bogging. This will make getting the screws out someday a bit easier: no bog in the grooves!

Jim

What a good idea - why didn't I know this.

[cpisz]

While not what I would want, I believe that the through bolts are a time honored way of doing this. The large seacocks on my current boat are like this and have been in place for decades. Not sure about the SS bolts though. I would have three yard replace those with bronze.