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post #1 of 21 Old 04-19-2019 Thread Starter
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Thru Hull Modification

I have purchased new thru hulls and seacocks for my Catalina 30.
The new thru Hulls are smaller (both in diameter and width to the originals).
Thought I had it worked out with distributor but miscommunication resulted in this situation.
Diameter difference old 2-3/8" new 1-1/2"
Width difference old 3/8" new 1/4"

Any suggestions on best way to fill in area around and secure new thru hull.
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post #2 of 21 Old 04-19-2019
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Re: Thru Hull Modification

Exchange them.
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post #3 of 21 Old 04-19-2019 Thread Starter
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Re: Thru Hull Modification

The better seacocks do not come with the original size thru hulls
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Re: Thru Hull Modification

Photos of both thru hulls
Attached Thumbnails
Thru 1.jpeg   Thru 2.jpeg  
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Re: Thru Hull Modification

That is a huge difference in diameter and an even bigger difference in area of the opening. Assuming there was a reason they used the large one in the first place (what are these for? Head plumbing?) I'd be extremely hesitant to make this switch.
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Re: Thru Hull Modification

The diameter dimension is the outside diameter of skin, the opening is the same.
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Re: Thru Hull Modification

Since those are tapered flush mount through hulls, the only real fix is to laminate up layers of glass till it's flush, fair and than redrill and countersink for the new through hull. I had a similar problem only the new through hull was not a flush mount and had a large enough diameter that it overlapped the counter sunk part enough to just fill the void with caulking.

If the old through hull is bronze could you reuse it with the new seacock??
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post #8 of 21 Old 04-20-2019 Thread Starter
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Re: Thru Hull Modification

Quote:
Originally Posted by roverhi View Post
Since those are tapered flush mount through hulls, the only real fix is to laminate up layers of glass till it's flush, fair and than redrill and countersink for the new through hull. I had a similar problem only the new through hull was not a flush mount and had a large enough diameter that it overlapped the counter sunk part enough to just fill the void with caulking.

If the old through hull is bronze could you reuse it with the new seacock??
The thru hulls are all composite and are probably original. The seacocks were a combination of bronze and plastic.
Seemed like a good idea to change all at the same time and I was trying to stay away from metal below the water line,

Even if the originals could be used the thread size is different. Thanks for your feedback.
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Re: Thru Hull Modification

Quote:
Originally Posted by Jac123 View Post
The diameter dimension is the outside diameter of skin, the opening is the same.
Got it - that makes sense now. That's quite a difference in thickness.
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post #10 of 21 Old 04-22-2019
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Re: Thru Hull Modification

Quote:
Originally Posted by Jac123 View Post
Photos of both thru hulls
Hi, if you were to have the old fitting machined to act as a washer for the new fitting through it, effectively acting as a washer to reduce the old hole to the correct size for the new fitting then when installed with an appropriate sealant it should work exactly as planned. You could probably achieve this by cutting the head off the old and counterboring for the new, but a lathe would do a better job. The thread dimensions appear to be similar, although not the same so precludes using the old fitting with new seacock but it should fit perfectly, if done right.

Cheers, Uncle Bob the 1st from Sydney Aust.
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