New thru-hulls/seacocks - SailNet Community
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post #1 of 28 Old 03-05-2007 Thread Starter
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New thru-hulls/seacocks

I want to replace all of my thru-hull fittings and seacocks, and am gearing up for the job. I've read through the other threads on this, but have one remaining question:

It seems that one can either put screws through the hull to secure the flange on the seacock, or use the nut on the thru-hull fitting to secure it, and have the valve just supported by the fitting. What are the pros and cons of each approach? Obviously, I'm nervous about drilling and countersinking holes in the hull.

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Eric
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post #2 of 28 Old 03-05-2007
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I'm in a similar situation. I have a 1990 Schock 23 with the original plastic thru hulls with separate bronze valves. It's time to change them all out.
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post #3 of 28 Old 03-05-2007
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You really need to have a backing plate, made of starboard or solid fiberglass, inside the hull, as this will provide a flat surface for the thru-hull nut to seat onto. You should probably also screw or bolt the seacock flange to the backing plate to give the seacock extra support.

If you have a cored hull, it would definitely be in your best interests to make sure the hull in the section with the thru-hull is either solid glass and not cored, which is often done by the boat manufacturer, or if the thru-hull is in a cored area, the holes are properly potted with the core removed for at least 1/4-1/2" and filled with thickened epoxy.

My favorite thru-hull fittings are these...but they're a bit pricey. However, they will probably be the last ones you'll ever have to buy.

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post #4 of 28 Old 03-05-2007 Thread Starter
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Ah, ok. So the valve acts as the nut for the fitting, tightened against the backing block, and then the flange just gets screwed to the block with wood screws?

I read Don Casey's article on the subject here: http://www.boatus.com/boattech/casey/07.htm

He suggests using screws through the hull, block, and flange, countersunk into the hull, and nutted on the flange. I think I'm more comfortable with your suggestion. It would still prevent the valve from rotating relative to the fitting, assuming the block wasn't able to rotate relative to the hull (which it wouldn't).

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No. There is a separate nut for the thru-hull fitting. While I normally agree with Mr. Casey, I don't see a point in drilling three more holes through the hull, albeit small ones. By screwing the flange to the block, you've effectively gotten the same result—preventing the seacock from turning the thru-hull fitting, with fewer holes. Ideally, the block should be either glassed to the hull... and it won't move. Make sure what ever screws you use are long enough to securely enter the block, but not long enough to exit the other side and damage the inner fiberglass skin of the hull.

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Oh, ok. So the flange on the seacock won't be flush with the block - there will be a separate nut in between?
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Dawg...I'm with you on the screws issue. No need for them.

Ereuter...yeah...think of them as two separate components...through hull and nut form one unit. Seacock threaded on is the other. This allows you to remove seacock without a haulout...assuming you have a teak plug for the through hull handy. (One should be wired in place right there to have it handy if seacock fails.)
If wood is used for the backing plate it should be glassed in place to avoid rot and future problems.
If you don't want to spring for titanium...I like marelon way better than bronze.
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Pine is generally better for the plugs... as it will swell up and hold itself in place once it gets soaked. I don't think teak will do that. Also, needs to be kept in a plastic bag and dry, for same reason. Should be held in place with light string, not wire...wire will corrode and is harder to cut or break.

I'd avoid wood for a backing plate for several reasons.. .

1) if it does get wet, it will change in size
2) if it does get wet, it will eventually rot and weaken
3) Even if it is glassed in place, if water gets to the wood... it will rot

Cam- I actually think there should be screws from the seacock flange into the backing block, but I disagree with Casey about them having to be through-bolted through the hull and block. The screws will serve to help prevent any torque on the seacock or its handle (if it gets stuck) from twisting the thru-hull fitting itself, and possibly breaking the sealant's seal.

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post #9 of 28 Old 03-05-2007
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It may just be me but I think the best installation is to make a solid fiberglass pad inside the boat. Drill the hole for the bronze thru-hull and use the thru-hull to hold the bronze seacock in place while you drill for thru-bolts. Countersink on the outside for the silicon bronze bolts and take everything apart to add bedding compound and then bolt the seacock in place. Now bed the thru-hull and screw that in place discarding the nut that came with the thru-hull. Add your bonding wire and attach the hose and you are done.
It may be old-fashioned but it works for me,
Robert Gainer
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Dawg...right...actually I think mine are balsa or something like that...much lighter than pine.
I thought you were talking abou the through hull being screwed. I agree about the sea-**** flange to the starboard or wood backing plate...not into the hull. How do you affix starboard to the hull...I thought nothing like 5200 would stick to it?
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