Through-Hull to Ball Valve Joint

D

dkinzer

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Sep 22, 2021
277
Hunter 41AC 0 Portland, OR
One of my seacocks is slightly stiff to operate. I've put light oil on the valve stem and let it sit a few days and it improved but it still is more stiff than all of the others. I have a new Apollo 70-105-10 valve to replace the existing one of the same model and if I have time during an upcoming hanging haulout I'll try to replace it.

My question is how to seal the joint between the through hull (which has straight threads) and the valve body (which has tapered threads? Perhaps some 4200 would work?
 
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D

dlochner

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Jan 11, 2014
11,440
Sabre 362 113 Fair Haven, NY
Nothing will safely seal that. You need to use a ball valve with straight threads. Shop around, there may be an adapter fitting to mate the straight and tapered thread.
 
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Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
6,492
Hunter 310 West Vancouver, B.C.
The best sealant for this is three wraps of teflon tape and then cover the tape with a light smear of Permatex #2.

The teflon provides the body to fill the gap and the Permatex provides the penetration to get to the root of the threads which do manage to engage. Watch the direction of the threads when wrapping and wiping.
 

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D

dkinzer

.
Sep 22, 2021
277
Hunter 41AC 0 Portland, OR
I didn't see an adapter on the current installation and the part numbers of the valves are identical.
 
Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
6,492
Hunter 310 West Vancouver, B.C.
90% of all production boats put in the NPS to NPT joint strictly for cost saving. I like to check that at boat shows. Always gives me a smile.

This is the proper fitting but costs too much for a production boat:

1678829055885.png
 
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D

dkinzer

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Sep 22, 2021
277
Hunter 41AC 0 Portland, OR
Ralph Johnstone said:
This is the proper fitting but costs too much for a production boat:
Click to expand
I've seen those and that seems to be a superior solution. If I were going to be on the hard for several days or more I would opt for re-working all the through hulls using the flanged fittings and a backing plate other than marine plywood.
 
D

dlochner

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Jan 11, 2014
11,440
Sabre 362 113 Fair Haven, NY
Ralph Johnstone said:
90% of all production boats put in the NPS to NPT joint strictly for cost saving. I like to check that at boat shows. Always gives me a smile.

This is the proper fitting but costs too much for a production boat:

View attachment 213748
Click to expand
There are ABYC standards for through hull fittings which require the ability to withstand a specified amount of side pressure. The adaptor @Ralph Johnstone mentioned is designed to meet this specification.

dkinzer said:
I've seen those and that seems to be a superior solution. If I were going to be on the hard for several days or more I would opt for re-working all the through hulls using the flanged fittings and a backing plate other than marine plywood.
Click to expand
Each to his own. The cost of adding a few days off on the hard storage is, IMHO, pretty small when compared to a failed or chronically leaking through hull fitting. The cost of the haul out may make a dent in your bank account, but nothing like the dent in the sea bottom if the fitting fails. Your boat, your money. :beer::beer:
 
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Dalliance

Dalliance

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Oct 6, 2007
1,024
Hunter H30 1982 Chicago IL
Don’t try to combine tapered and straight threads. It’s not safe. Use a straight thread seacock that mates securely with the straight thread through hull or use the adaptor that Ralph Johnstone recommended to transition from the straight thread through hull to a tapered thread ball valve.
 
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Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
6,492
Hunter 310 West Vancouver, B.C.
Dalliance said:
Don’t try to combine tapered and straight threads. It’s not safe.
Click to expand
I fully agree. But as I said, 90% of all production boats are done that way. My '99 H-310 being one of them. Look at your own boat. Unless you see a flanged adapter on the floor, you have an NPS to NPT joint.
 
D

dlochner

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Jan 11, 2014
11,440
Sabre 362 113 Fair Haven, NY
Besides leaking, the reason mismatched threading should not be used is the exposed threaded area is very weak. It's strength is limited by the thickness of the tubing in the threads which is much thinner than the the outside diameter of the fitting. A proper straight threaded fitting has no exposed threads, this is very robust. Tapered threads have a thicker wall at the tapered end of the threads, proper tapered threads have very few exposed threads. Those exposed threads are very shallow making the joint stronger than a tapered/straight fitting.
 
Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
6,492
Hunter 310 West Vancouver, B.C.
Meh, yes thread depth does have a slight theoretical bearing on the overall strength of the assembly but the whole story can be told in just one picture :

1678897683838.png


.................... and that is "solid thread engagement". I use the word "solid" as only the first two threads on the LH side are solidly engaged. The short engagement creates much higher stresses due to the leverage on the short engaged section.

Notice also that the area of engagement in the LH NPS to NPT involves the thickest root threads of the male NPS section to the thickest root threads of the female NPT threads. Lots of muscle there.

The greatest problem you face with the NPT to NPS interface is leakage, so back to post #3. Second, is the through hull in an area where it could be subject to high impact ? If so, install a proper through hull. All of my through hulls are in enclosed locations where the danger of impact is zero. All except the head sea water intake. I'm still thinking about that one.

1678898688994.png
 
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BigEasy

BigEasy

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Jun 21, 2004
2,533
Beneteau 343 Slidell, LA
There is another option that is rarely mentioned that eliminates the problem of mis matched threads. Groco offers a full line of bronze thru hull fittings, valves, strainers, & tailpieces that have common british pipe parallel threads, on all components, that ensure complete thread engagement / mating of the components. Certainly not as robust as a proper thru hull fitting; however, I am not crossing oceans. For coastal cruising, I believe The BSPP fittings are adequate. I wrap the threads with teflon tape and apply a bit of 4200. I haven't had one leak or fail in 30 years.
 
Tally Ho

Tally Ho

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Jan 7, 2011
4,788
Oday 322 East Chicago, IN
Ralph Johnstone said:
I fully agree. But as I said, 90% of all production boats are done that way. My '99 H-310 being one of them. Look at your own boat. Unless you see a flanged adapter on the floor, you have an NPS to NPT joint.
Click to expand
Mine (3 of them) are like this…no flange, just the skin fitting and a gate valve.

I agree a proper seacock would be ideal, but I don’t think most boats (and in particular lighter production boats not intended for blue water) are like mine.

Greg
 
Dalliance

Dalliance

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Oct 6, 2007
1,024
Hunter H30 1982 Chicago IL
Ralph Johnstone said:
I fully agree. But as I said, 90% of all production boats are done that way. My '99 H-310 being one of them. Look at your own boat. Unless you see a flanged adapter on the floor, you have an NPS to NPT joint.
Click to expand
Agreed, but there is one exception to that, though not likely encountered in an unaltered production boat, especially older ones.
Marelon ball valves and seacocks are actually NPS, so they’ll fit directly on a NPS through hull that’s either Marelon or bronze. The more commonly encountered bronze ball valves, Groco and others, are NPT and require the adaptors to properly mate with NPS through hulls. I’m not selling Marelon, but they do address the NPS/NPT problem.
My 1982 H30 had antiquated gate valves screwed direct to through hulls or to 90° elbows for some reason. I‘ve replaced them all with ball valves that I actually operate weekly. Two are Marelon and two are bronze.
 
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Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
6,492
Hunter 310 West Vancouver, B.C.
Dalliance said:
Maralon ball valves and seacocks are actually NPS, so they’ll fit directly on a NPS through hull that’s either Maralon or bronze.
Click to expand
1678933339025.png


Wow, live and learn. Far simpler than going with the bronze adapter to NPT. The bronze adapter still requires that you install the three bolts from the underside of the hull to hold the adapter plate in position.

Sees to me that someone on this site got into a pi$$ing match with a supplier who told the purchaser to only use teflon tape on the NPS threads. I think that by now we all know how that's going to work out.
 
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thinwater

thinwater

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Mar 26, 2011
3,416
Corsair F-24 MK I Deale, MD
dlochner said:
Nothing will safely seal that. You need to use a ball valve with straight threads. Shop around, there may be an adapter fitting to mate the straight and tapered thread.
Click to expand
^^ This.

Do not use an addapter. the farther you extend from the through-hull the greater the leverage on the fitting if anything strikes it, and most don't meet ABYC standards anyway. Get the right valve.
 
Tally Ho

Tally Ho

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Jan 7, 2011
4,788
Oday 322 East Chicago, IN
thinwater said:
^^ This.

Do not use an addapter. the farther you extend from the through-hull the greater the leverage on the fitting if anything strikes it, and most don't meet ABYC standards anyway. Get the right valve.
Click to expand
So, they sell a ball valve with straight threads (at least on the inlet side)?

I replaced the skin fitting on one of mine last year, and I think it screwed pretty deep into the valve…maybe it is has straight threads.

Greg
 
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