Thru Hull vs Hole Size

[commander500]

Replacing cockpit drain thru hulls. These are just below the water line. Removed old plastic 1 1/2" hose thru hulls with same but SS. Just noted the new thru hull has almost a 1/2" play inside the thru hull "hole". I could tighten the thru hull nut real good and just use a good blob of 4200 but it doesn't feel right. Any proven suggestions - backing plate with correct hole size, filling and re-drilling, some type of bushing?

[GordMay]

See Rod Collins' excellent tutorials at https://marinehowto.com/
Including:
Seacock & Thru-Hull Primer ➥ https://marinehowto.com/seacock-thru-hull-primer/
Replacing Thru-Hulls and Seacocks ➥ https://marinehowto.com/replacing-th...-and-seacocks/
Seacock Backing Plates ➥ https://marinehowto.com/seacock-backing-plates/
and much more ...

[Pete7]

Not a good use for stainless steel, choose bronze or plastic to avoid crevice corrosion.

You might consider going up to 2" with new pipes etc rather than try and fill in the wholes, particularly for cockpit drains.

Pete

[tkeithlu]

If you've got a good grip on the hull with the mushroom and the backing nut, you're fine with the 3M 5200 solution. If in doubt, use a backing plate with right sized hole and decide whether to glue it in place or through bolt it.

[Cadence]

Get the correct size for the existing holes, not in SS. 1/2" is a lot of play for one below the WL.

[s/v Jedi]

If the hull is fiberglass, then either upgrade to a larger size fitting (preferred) and use either a reducer or upgrade hose too.

I also agree that you should go to bronze (Rod Collins info, use Groco flanged adapters etc.)

For steel boat, stainless steel makes sense. You can buy the Groco hardware in stainless as well or just weld.

[Cheechako]

Originally Posted by Cadence

Get the correct size for the existing holes, not in SS. 1/2" is a lot of play for one below the WL.

Yeah, something wrong there....

[Delaware]

All good answers above. Purchase a bronze thru hull in that fits your hole snugly and 5200 in then adjust the plumbing to it accordingly.

[jmschmidt]

If you have a solid glass layup hull you can grind out the area and install a proper multi-layered hull patch and redrill the hole for your new thru-hulls. If you have a cored hull probably not.

[Gary Mc]

Do the hoses lead from essentially thru hull type fittings in your cockpit sole?

2 inch is a pretty standard size for cockpit drains. I would check the fittings in the cockpit to see if they are undersized for the hole as well. If so replace every thing with 2 inch.

[commander500]

Appreciate all feedback. About SS under WL, I guess true. With cockpit drains I believe size matters. I will study going up to 2".

Again, thanks to all. Great advice each one. Good to have other's perspective and experience.

[Celestialsailor]

There is absolutely no reason to use 5200. 4200 works just fine and is removable. There is very little water pressure at the seal of a thru-hull.

[s/v Jedi]

I actually prefer a polysulfide sealant for thru hull fittings. Now that 3M 101 is gone, LifeCaulk is one I know and use.