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Compass Marine How To | all galleries >> Welcome To >> Seacock Backing Plates / Alternate Method / No Through Bolts > Install Flange or Seacock
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Install Flange or Seacock

Once the studs are in simply drop the flange over it put on the nuts. You're now ready for a dry test fit in the hull.


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Todd 16-Feb-2015 23:47
I wound up purchasing a very similar product from Fisheries Supplies (local here in Seattle, WA). These commercially produced fiberglass backing plates have predrilled holes and brass nuts that you press fit from the bottom. After glassing the backing plate in, you secure the flange to the plate with a ss bolt. This worked great 3/4 times. But in one instance, we cocked the nut slightly during dry fitting. Then I hamhanded a wrench and totally cross threaded the bolt into the nut...and then the nut started spinning. The only option we had was to muscle the bolt and nut *through* the fiberglass backing plate... something that should have been near impossible. Without the nut in it's hole, I'm going to have to resort to thru-bolting after all. Sigh. These look more bomber than what I purchased...but that said, I'd have preferred to have thru-bolted right from the start. You can see photos at
Rob 06-Nov-2013 21:18
I have used this method with two variations. After laying up the backing plate I cover the uncured layup with cellophane and set the flange on top. The weight of the flange creates an imprint into the backing plate that the flange then fits snugly into when cured and further restricts rotation. I have also tapped from the bottom of the backing plate set hex head bolts in epoxy. Use a router but to counter sink for the hex head. Now the bolt can't be pulled through.
Michael 09-May-2011 21:41
You may want to make your studs long enough so that you can get two nuts on it with the flange installed. This will give you the option to remove the studs and screw off the sea cock, in case you are unable to remove the thru Hull from the bottom.
sean 31-Jan-2010 06:32
great idea as it seems you can pe-fab your flanges and plate smuch more accurately "dry" then epoxy attach to the hull cmbined with the thread strength of the through hull.Got to be equal if not a superior method than the hull bolted method? given the increased accuarcy, and less holes ct through the hull!?