Does this seacock need a backing plate?

[IH82BL8]

I've drilled a 1" hole through the side of the sump where the bilge pump and float switch are located in order to install a seacock. The seacock has a triangular flange. The hull is 1/2" thick in that area. I'm planning to cut away the liner. Is the hull thick enough for the seacock, or do I need to add a backing plate.

Also, if I install a backing plate, I'm considering laying up a fiberglass plate to the outside of the hull rather that trying to work in the sump.

Any input would be appreciated. Thanks.

 

[Rich Stidger]

I tend to think that all seacocks and thru-hulls should have a backing plate, but maybe that is overkill. I know that I have a thru-hull in s similar location and it has a piece of wood for a backing plate.

As for an outside plate, I would work it inside for a more esthetic job. I'll see if I can add a picture to the post later- edited to add two pix, one outside of the thru-hull with hinged cover for cleaning and the inside with a round wooden backing plate.

 

[readerbill]

http://www.pbase.com/mainecruising/replacing_thruhulls

I'm with Rich, In my opinion all thru hulls need backing. The above site has great info and how to's under its article section. I would suggest checking it out and noting the two types of theads so you don't miss match them. I just finished installing fiberglass backing and replacing my factory valves with true seacocks and found the site a really big help.
Bill

 

[nmenkes]

Sure it needs a backing plate.
and preferably from wood with a metal plate of the same metal of the seacock with a eyelet to connect the earthing wire on top of it.
the wooden plate will help strengthening the ares around the hole,
and the metal plate will give better grounding of the seacock.
remember?! you need to ground the sea cock.

 

[IH82BL8]

Hey Bill,

I read that article a few weeks ago which is why I wanted to go with a fiberglass plate instead of a wood plate.

 

[Sailvayu]

Structurally there is no reason to use a backup block. This thinking is left over from the days of wood boats when they were used to reinforce a hole in the plank which of course would weaken the plank. It adds little to a FRP hull. That said many thru hulls are not treaded far enough to work on a thiner FRP skin. If you need a spacer for that reason I recommend a FRP plate not wood or metal. You could also simply layup a few layers of glass first and drill thru all of it in one shot.

 

[readerbill]

Its sound like we are on the same path I've tried to post pictures of my projects on my member page here as I progress. If you do go the route suggested on that link I would suggest following his steps as close as possible. I deviated a couple of times and it cost me more time and effort equating of course to more $. Keep us posted I am interested in what you finally decide and how it turns out. Good luck.