Through hull fitting extension for livewell plumbing

[Thirsty Endgrain]

Hi all,

I'm planning for my livewell, intending to use one of the Groco filtered pickups.

Plumbed through the hull into a seacock. The issue I'm running into is the space under my floor to the hull is between 4-6" or so, and the threads on the water pickup are about 2 3/16" long, quite short of making it through the space under the deck. Normally I would use a coupling here of course, with a nipple to get to the seacock. But being that the threads on the through hull fitting and seacock are NPS, not NPT, and I can't seem to find NPS couplings, is it acceptable to use NPT fittings there? I'd have to use an NPS nipple for the extension as the female threads on the seacock are also NPS.

I'm familiar with plumbing in general, but I've never run into this particular situation, and would appreciate any advice. I can draw up a little diagram later to help with the visualization of what I'm trying to accomplish. Thanks in advance.

 

[Scott Danforth]

No

 

[dingbat]

Thru hull fittings and seacocks have NPS thread to restrict the use of ordinary plumbing components, ie not bronze or approved for marine use

 

[Thirsty Endgrain]

No I can't extend the fitting?

I looked through McMaster for bronze couplings but didn't see any.

Is there a solution to increasing the length of the through hull to the seacock?

 

[Scott Danforth]

No I can't extend the fitting?

I looked through McMaster for bronze couplings but didn't see any.

Is there a solution to increasing the length of the through hull to the seacock?

Look in a marine catalog

Mcmaster is an industrial supply house

NPS or barb to barb with a hose

 

[Thirsty Endgrain]

Ok, read all of the groco literature I could find.

Their STH series through hull scoops are a combination thread. NPS for most of the shaft, and NPT just at the tip, allowing for the use of either direct mounting to a seacock, which has NPS threads, and relies on a ring of sealant at the base of the female threads to create the seal; or seemingly, connection to another NPT type fitting.

It took reading this a couple of times to differentiate the installation methods, but this guide seems to work out.

https://www.groco.net/media/file/file/i/b/ibv-fbv-tech-blltn.pdf

 

[dingbat]

Not sure what your trying to do that you need an NPT fitting.

My pump intake is setup like the one on the left.

NPS (scoop fitting) thru hull to NPS seacock. Out NPS seacock to NPS hose to pumps

 

[Thirsty Endgrain]

Maybe a pic will help clarify. I need to get through the inaccessible space between my hull and deck. If the Groco through hull came with longer threads it wouldn't be an issue, but I've got at least 3" that needs to be made up. Trying to figure out if I'm missing something, making it more complicated, etc. I know I'm going to need to cut a bigger hole in the deck to be able to get the backing nut onto the pickup, but I'm just wondering what is the proper way to extend the through hull threads into a seacock?

 

[Thirsty Endgrain]

Actually, I may just go with a transom mounted pump. This is probably more work than it's worth.

 

[Scott Danforth]

per your picture, you have to access the non-accessable space. just cut a hole in the deck, glass in a pocket down to the hull.

 

[Thirsty Endgrain]

per your picture, you have to access the non-accessable space. just cut a hole in the deck, glass in a pocket down to the hull.

Didn't think of that. Still may just go transom mount, but I'm trying to limit the amount of things back there. It's not a huge boat, but I could fit one.