replacing seacocks with a base flange - SailNet Community
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post #1 of 2 Old 12-06-2011 Thread Starter
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replacing seacocks with a base flange

It appears that on my 1977 Tartan 34C, there are two 1/2'' through-hulls, one for the galley sink and one for the head-intake. They both are directly connected to a ball valve (looks like this: ) and do not have a flange base that spreads the load over a larger area of the hull (as in this proper seacock: ). Not having such a base seems to be risky if I ever would venture off-shore, right?

There are two issues for which any comments and suggestions would be greatly appreciated:

1. I am planning to replace and rebed the through-hulls and replace the valves with a seacock with a flanged base. BUT in order to not have to drill more holes into the hull for the bolts, I am considering adding a backing plate of sorts fitted to the hull, with bolts that keep the base flange of the seacock in place, but do not penetrate the hull. I am not exactly sure how to do that last part best. Does anyone have experience with this?

2. There is also a larger seacock (1 1/4") for the head discharge. This installation has, at its base, a little 'hill' on the inside of the hull. My guess is this is factory-built. Does anyone know what this is for? The smaller through-hulls don't have this and go straight through the hull.

3. My assumption is that all Tartan 34C hulls are NOT cored below the waterline but made of solid fiberglass only. Anybody can back this up?



Last edited by Faster; 12-06-2011 at 02:06 PM. Reason: defeating auto-porn filter
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post #2 of 2 Old 12-06-2011
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Here's a link explaining how to install flange adaptors without drilling extra holes through the hull: Seacock Backing Plates / Alternate Method / No Through Bolts Photo Gallery by Compass Marine at

Double check the diameters -galley sink drains are usually 3/4"

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