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post #1 of 2 Old 09-13-2004 Thread Starter
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Thru Hull Replacement

I just removed old corroded thru hulls this weekend on my Bristol 29''9. I have purchased new thru hulls and Apollo flush mount seacocks as replacements.

When I removed the old bronze, I was surprised to find the hull was only 1/2" thick where all thru hulls were mounted. I plan to mount the new hardware on a 3/4" epoxied plywood backing pad.

The seacock is secured by screwing directly into the thru hull. Three machine screws, flush mounted from the exterior hull up through the backing pad and through eyes on the seacock are also part of the configuration.

My concern is this: if the hull is only 1/2" thick and I countersink the mounting screws, that will leave me with 1/4" or less actual hull material through which the screws will be situated. Now, even though these screws will be covered in 5200 and the backing pad will be secured to the hull with 5200 - the hull just seems a little thin. Any advice or comments out there on this? Anyone who has changed their thru hulls must have encountered this.

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post #2 of 2 Old 09-13-2004
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Thru Hull Replacement

I just added a new thru hull for a salt rinse on the anchor pulpit. Mine was a bit thicker but not to matter. Use a bigger area 3/4" Teak or if you must Epoxied Plywood backing plate to spread the load. I think you will be fine with the countersink, just remove only as much as you need to flush it. At 1/4", still the head of the machine screw is flush with the hull and compressed in the countersink, and that load distributed over the back plate so I can''t see it pulling through or failing.
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