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Through Hulls
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andrewb
Geelong, Australia
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January 30, 2018 - 4:27 am
Member Since: October 18, 2015
Forum Posts: 10
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Dose anyone know what the thread is on the through-hull fittings for the cooling water? It looks about 1", but is it BSP or NPT?

 

Andrew.

 


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Scott Carle
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January 30, 2018 - 8:54 am
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It depends on what brand/type of thru hull fitting it is. These were not a standard item from year to year much less boat to boat. I think they just purchased in bulk whatever happened to be available at the time at the best price. 🙂 second very few of them are still on our boats, This is an item that get's replaced. Not a lot but over the 30+ years these boats have been out there, it is a good bet that it isn't original to the boat. So no easy answer.

 

Here are some more in depth articles on them in general that might help you. If you read these three sites and follow their directions you can't go wrong.

http://www.pbase.com/mainecrui.....ock_primer

https://www.sailfeed.com/2013/10/no-nos-and-good-practice-with-thru-hulls-and-seacocks/

https://www.jamestowndistributors.com/userportal/document.do?docId=538

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Scott Carle DE38 Cutter s/v Valkyr
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Argyle38
US Northeast
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February 4, 2018 - 11:27 pm
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Mine is a 1" NPT, original equipment, but like Scott said, that might not mean anything for your boat. I believe mine is Conbraco, but it could be something different. It's a tapered wedge type. If you have a stainless steel ball valve type, it's probably not original. If it's a tapered wedge, then it might be.

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andrewb
Geelong, Australia
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February 5, 2018 - 4:33 am
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Investigated further..... I have what appears to be a 3/4" ball valve (may be brass!!!... eeeek!) screwed onto the through-hull. A male-male coupling in the top of the valve isn't coming out any time soon. The part I did manage to unscrew off the end of this is 3/4" NPT. I'm assuming the male thread left in the valve is also NPT, but I need to go back with a set of callipers I can get in there to check if it is tapered or not. There were only about 3 threads holding it on so it could have been a female NPT onto a male NPS. Whatever it is the fun is sourcing NP thread fittings down-under!

I spoke with the Forespar distributor about the Marelon fittings, but they are NPS so not usable, unless the thread left on the valve is indeed NPS. Forespar use some interesting terminology: a quote from one of their pieces of literature states: "Marelon plumbing fittings have NPT parallel threads"

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Scott Carle
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February 5, 2018 - 8:51 pm
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ok you definitely have an issue. You should be able to thread it on all the way till it bottoms out on the threads. If it is only getting a 3 thread bite before you can't turn it then you have mismatched thread types. Not safe as at three threads you don't have a full strength connection. If it froze the ice could probably push the fitting right off the end of the  through hull. Also possible it could come off if you gave it a bad whack. I would just buy a quality dedicated through hull fitting and make sure it is right. read the articles on the links I posted.

 

Oh... i think ours is 3/4 inch in size also for the intake for the engine. just for the record.

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Scott Carle DE38 Cutter s/v Valkyr
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Patrick Twohig
San Diego, CA
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August 1, 2018 - 1:00 pm
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So this is a really common mistake people make.  A ball valve is not a proper seacock.  Lots of people are under the misguided assumption they can just stick a collar on the thru hull and then slap a ball valve on it.  The problem is that every time you reef on that valve to operate it, you're putting all the torque on the thru-hull stem which could snap off.  The stem is designed first to channel water, not bear a load.  Therefore a good and proper seacock has a flange that bolts through the hull that transfer that torque to the hull.

Thru-hull stems are NPS as well as a seacock.  That way you can mate the seacock flush with the hull and bolt it properly.  Ball valves are almost certainly NPT, which is why you have only three threads on there.  It's just not a compatible setup.  Somebody redneck repaired that at some point because they were too cheap to pay a boatyard.

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