Installing Seacocks - Follow Up Info !!

[Maine Sail]

Hi All,Since posting the article/blog on installing seacocks I've had a lot of emails and questions regarding the "mismatching" of different thread types such as NPS and NPT.Ross put me up to the challenge so last night I made a cut away view to show why using two different threads is really not such a good idea.I basically used a bronze nipple or threaded pipe with standard plumbing threads of NPT (National Pipe Tapered) and a bronze coupling also the industry standard of NPT thread. NPT threaded fittings are the thread pattern sold at all marine stores for things like elbows, valves, nipples, couplings and hose barbs.I cut the bronze coupling almost in half, for a cut away view, so I could thread the NPT bronze nipple into one side and an NPS through-hull fitting into the other. I then sprayed each with a McLube, to reduce friction but save the picture quality, and threaded both the NPT nipple and the NPS through hull into the cut-a-way bronze coupling, by hand, and until I had sufficient yet equal resistance on each. The results even surprised me! As you can clearly see the NPT nipple threaded into the NPT coupling a LOT further than did the NPS through-hull. If you were to take a wrench to both you might get one more turn at best out of the NPS through hull but you may get two or three full turns out of the NPT nipple. If you look very closely at the picture you can see that the outer threads of the through hull are already NOT fitting tightly against the female threads of the coupling and the inner few threads are quite tight or virtually bottomed out...!!! The square peg evidently does NOT fit a round hole..! This coupling represents the threads of an in-line valve. Most ALL ball valves or gate valves have NPT or tapered threads and most all through hulls have NPS or straight threads. We finally have a definitive answer, and photographic proof, and can clearly see from the photo how potentially dangerous it is to stick a ball valve directly onto a through hull.. Sticking a ball valve directly onto a through hull gives you about four or five threads between sinking and floating so I'd suggest just not doing it. It's probably best to use proper seacocks with flanges and the correct and matched threads..!!

 

[Maine Sail]

Hi All,Since posting the article/blog on installing seacocks I've had a lot of emails and questions regarding the "mismatching" of different thread types such as NPS and NPT.Ross put me up to the challenge so last night I made a cut away view to show why using two different threads is really not such a good idea.I basically used a bronze nipple or threaded pipe with standard plumbing threads of NPT (National Pipe Tapered) and a bronze coupling also the industry standard of NPT thread. NPT threaded fittings are the thread pattern sold at all marine stores for things like elbows, valves, nipples, couplings and hose barbs.I cut the bronze coupling almost in half, for a cut away view, so I could thread the NPT bronze nipple into one side and an NPS through-hull fitting into the other. I then sprayed each with a McLube, to reduce friction but save the picture quality, and threaded both the NPT nipple and the NPS through hull into the cut-a-way bronze coupling, by hand, and until I had sufficient yet equal resistance on each. The results even surprised me! As you can clearly see the NPT nipple threaded into the NPT coupling a LOT further than did the NPS through-hull. If you were to take a wrench to both you might get one more turn at best out of the NPS through hull but you may get two or three full turns out of the NPT nipple. If you look very closely at the picture you can see that the outer threads of the through hull are already NOT fitting tightly against the female threads of the coupling and the inner few threads are quite tight or virtually bottomed out...!!! The square peg evidently does NOT fit a round hole..! This coupling represents the threads of an in-line valve. Most ALL ball valves or gate valves have NPT or tapered threads and most all through hulls have NPS or straight threads. We finally have a definitive answer, and photographic proof, and can clearly see from the photo how potentially dangerous it is to stick a ball valve directly onto a through hull.. Sticking a ball valve directly onto a through hull gives you about four or five threads between sinking and floating so I'd suggest just not doing it. It's probably best to use proper seacocks with flanges and the correct and matched threads..!!

 

[Ross]

Mainesail, Good work !! I couldn't find any scrap

to try that with. It appears that people can get away with standard tapered pipe fittings on thru hull fittings because of a generous amount of pipe dope to seal the leaks in this low pressure application. Certainly demonstrates that there is a lack of structural integrity in a thru hull to inline valve assembly.

 

[Ross]

Mainesail, Good work !! I couldn't find any scrap

to try that with. It appears that people can get away with standard tapered pipe fittings on thru hull fittings because of a generous amount of pipe dope to seal the leaks in this low pressure application. Certainly demonstrates that there is a lack of structural integrity in a thru hull to inline valve assembly.

 

[Akula]

NPT Through-Hull

I installed NPT Through-Hulls with NPT Ball Valves by cutting NPT threads on NPS Through-Hulls.Akula

 

[Akula]

NPT Through-Hull

I installed NPT Through-Hulls with NPT Ball Valves by cutting NPT threads on NPS Through-Hulls.Akula

 

[RichH]

This should clear up those 'differences'

www.colder.com/Portals/0/pdfs/NPT.pdffor the differences between pipe threads ..... tapered, straight, etc. NPT is plumbers 'stuff' but straight threads, etc. are for 'boiler' and strength type applications. Hope the above URL helps to straighten this all out. ;-0

 

[RichH]

This should clear up those 'differences'

www.colder.com/Portals/0/pdfs/NPT.pdffor the differences between pipe threads ..... tapered, straight, etc. NPT is plumbers 'stuff' but straight threads, etc. are for 'boiler' and strength type applications. Hope the above URL helps to straighten this all out. ;-0

 

[Maine Sail]

Akula..

Can you fill us in on the details of how you did this and where you got the proper equipment. Did you take it to a machine shop?

 

[Maine Sail]

Akula..

Can you fill us in on the details of how you did this and where you got the proper equipment. Did you take it to a machine shop?

 

[sailaway78]

You can use a pipe die

Mainsail, you can use a standard pipe die and cut NPT threads on a NPS pipe. I am not real sure how you would hold the thru hull, as a vice would certainly at a minimum mar the brass. But cutting the threads would not be a problem. Home Depot will cut pipe threads in the store, on stuff you buy there, not sure about something you bring in.

 

[sailaway78]

You can use a pipe die

Mainsail, you can use a standard pipe die and cut NPT threads on a NPS pipe. I am not real sure how you would hold the thru hull, as a vice would certainly at a minimum mar the brass. But cutting the threads would not be a problem. Home Depot will cut pipe threads in the store, on stuff you buy there, not sure about something you bring in.

 

[Ross]

Make a black locust clamp for the threaded

part of the thru hull. Bore a hole the outside diameter of the threaded portion. Saw a slot through the hole and a couple of inches past in a 1 inch thick piece at least an inch wider than the hole diameter. Put the thru hull in the hole and clamp the wood in a heavy vise. Now you can hold the piece without marring the threads.

 

[Ross]

Make a black locust clamp for the threaded

part of the thru hull. Bore a hole the outside diameter of the threaded portion. Saw a slot through the hole and a couple of inches past in a 1 inch thick piece at least an inch wider than the hole diameter. Put the thru hull in the hole and clamp the wood in a heavy vise. Now you can hold the piece without marring the threads.

 

[Maine Sail]

My concern.

My concern with this would be any more reduction in the thickness of the thru-hull it's self. If you look at the thickness of a thru-hull and then take the thread depth out there is NOT a very large cross section of bronze left. Perhaps this is why I cracked one when a spare alternator hit it in lumpy seas. My 3/4 inch thru-hull cost me $13.00. The 3/4 inch marine rated full flow bronze ball valve cost $13.65 and the 3/4 inch flanged adapter cost $17.00. For the $17.00 extra dollars people are willing to cut corners and be this risky with a five to six figure vessel?On my most recent boat purchase, our CS-36, my insurance company (Amica) made me replace all my through-hull's & valves with marine rated seacocks. They did however give me a full six months to get in compliance. They did not require, however, that they be through bolted, weird, but did require flanges and marine rated. After I installed them, and changed a bunch of other stuff they requested too, such as the bilge pump and some wiring, the surveyor had to come back and sign off. It's getting tougher and tougher to insure an older boat and they are requesting ABYC spec on many items...! Part of my problem was I hired a good surveyor and in his report he slammed the valve directly screwed onto the through hulls and recommended proper flanged seacocks which my insurance company upheld but added the marine rated part..I personally had an improperly installed through hull crack on me when a heavy item under the sink, a spare alternator, fell & hit the valve in rough weather. My boat did not sink, as it was just a small crack, and I found the problem in time, thank god for bilge alarms, but I could have lost it.There is a reason I'm passionate about this subject and it's because I've personally seen the consequences..I also found this little tid bit."Around 1987, the A.B.Y.C. established a set of “standards” for recreational watercraft that included guidelines for plumbing components. This was the early stage of the H-27 “Recommended practices and standards covering seacocks, thru-hull fittings, and drain plugs.” By 1989 this was published by the A.B.Y.C. and builders were encouraged to comply. By 1991 the Marine U.L. began incorporating the A.B.Y.C. standards into their standards. The biggest change from the original U.L. standard was the A.B.Y.C. addition of a 500 lb. load test applied to the “outermost fitting” (the tailpipe) of the valve “system”. This was the first time a seacock was viewed as a “system” including the thru-hull and tailpipe (or 90 deg. elbow) for hose attachment."So I guess if your flange-less through hull, with valve screwed onto it, can support a 500lb load test at the outermost fitting you're safe?? Mine was hit by an alternator and cracked which is hardly 500lbs.. I would not want to see the results of Michael Moore standing on the hose barb or outermost fitting of a "valve on a thru-hull" and he's only about 300 lbs.. On the contrary he and Rosie are both welcome to stand on my through bolted seacocks at the same time...

 

[Maine Sail]

My concern.

My concern with this would be any more reduction in the thickness of the thru-hull it's self. If you look at the thickness of a thru-hull and then take the thread depth out there is NOT a very large cross section of bronze left. Perhaps this is why I cracked one when a spare alternator hit it in lumpy seas. My 3/4 inch thru-hull cost me $13.00. The 3/4 inch marine rated full flow bronze ball valve cost $13.65 and the 3/4 inch flanged adapter cost $17.00. For the $17.00 extra dollars people are willing to cut corners and be this risky with a five to six figure vessel?On my most recent boat purchase, our CS-36, my insurance company (Amica) made me replace all my through-hull's & valves with marine rated seacocks. They did however give me a full six months to get in compliance. They did not require, however, that they be through bolted, weird, but did require flanges and marine rated. After I installed them, and changed a bunch of other stuff they requested too, such as the bilge pump and some wiring, the surveyor had to come back and sign off. It's getting tougher and tougher to insure an older boat and they are requesting ABYC spec on many items...! Part of my problem was I hired a good surveyor and in his report he slammed the valve directly screwed onto the through hulls and recommended proper flanged seacocks which my insurance company upheld but added the marine rated part..I personally had an improperly installed through hull crack on me when a heavy item under the sink, a spare alternator, fell & hit the valve in rough weather. My boat did not sink, as it was just a small crack, and I found the problem in time, thank god for bilge alarms, but I could have lost it.There is a reason I'm passionate about this subject and it's because I've personally seen the consequences..I also found this little tid bit."Around 1987, the A.B.Y.C. established a set of “standards” for recreational watercraft that included guidelines for plumbing components. This was the early stage of the H-27 “Recommended practices and standards covering seacocks, thru-hull fittings, and drain plugs.” By 1989 this was published by the A.B.Y.C. and builders were encouraged to comply. By 1991 the Marine U.L. began incorporating the A.B.Y.C. standards into their standards. The biggest change from the original U.L. standard was the A.B.Y.C. addition of a 500 lb. load test applied to the “outermost fitting” (the tailpipe) of the valve “system”. This was the first time a seacock was viewed as a “system” including the thru-hull and tailpipe (or 90 deg. elbow) for hose attachment."So I guess if your flange-less through hull, with valve screwed onto it, can support a 500lb load test at the outermost fitting you're safe?? Mine was hit by an alternator and cracked which is hardly 500lbs.. I would not want to see the results of Michael Moore standing on the hose barb or outermost fitting of a "valve on a thru-hull" and he's only about 300 lbs.. On the contrary he and Rosie are both welcome to stand on my through bolted seacocks at the same time...

 

[sailaway78]

I believe that

Mainsail,IMHO if you cut an NPT thread onto an NPS pipe nipple, you will have an NPT pipe nipple. Unless the ID of the NPS nipple is larger than the NPT you will have exactly the same wall thickness as the NPT.

 

[sailaway78]

I believe that

Mainsail,IMHO if you cut an NPT thread onto an NPS pipe nipple, you will have an NPT pipe nipple. Unless the ID of the NPS nipple is larger than the NPT you will have exactly the same wall thickness as the NPT.

 

[Maine Sail]

Nice n Easy

I agree 100% with that premise but the castings on a thru-hull fitting are different than that of a pipe nipple and the thru-hulls that I have seen have a tinner wall section to begin with. Thru-hulls are cut to be straight thread or a "combination" thread, according to Groco. A "combination thread" basically just rounds or squares off the tops of the first few threads creating in a sense, but not really, a taper. A combination thread, in my understanding, does not take any more meat out of thru-hull's thickness but rather takse the "tops" off the first few threads. I'm guessing you could do it but just know that the wall thickness of a thru-hull fitting is not the same as a standard pipe fitting as they are made differently and are not one in the same.I know many boats have incorrect mismatched threads and they are still floating. I'm merely presenting this information so folks can decide for themselves what is safe, proper and prudent and what will allow them to sleep at night.If you're comfortable with three or four threads of holding power that are a mismatch by all means use that combination.I will try and compare the thickness of a standard thru-hull fitting and a nipple and post it on my web site. I've already posted a new article which is basically a terms, definitions and descriptions primer to my other "Installing Seacocks" article. I'll add this thickness information to the site when I can get it done.. http://upload.pbase.com/edit_gallery/mainecruising/seacock_primer

 

[Maine Sail]

Nice n Easy

I agree 100% with that premise but the castings on a thru-hull fitting are different than that of a pipe nipple and the thru-hulls that I have seen have a tinner wall section to begin with. Thru-hulls are cut to be straight thread or a "combination" thread, according to Groco. A "combination thread" basically just rounds or squares off the tops of the first few threads creating in a sense, but not really, a taper. A combination thread, in my understanding, does not take any more meat out of thru-hull's thickness but rather takse the "tops" off the first few threads. I'm guessing you could do it but just know that the wall thickness of a thru-hull fitting is not the same as a standard pipe fitting as they are made differently and are not one in the same.I know many boats have incorrect mismatched threads and they are still floating. I'm merely presenting this information so folks can decide for themselves what is safe, proper and prudent and what will allow them to sleep at night.If you're comfortable with three or four threads of holding power that are a mismatch by all means use that combination.I will try and compare the thickness of a standard thru-hull fitting and a nipple and post it on my web site. I've already posted a new article which is basically a terms, definitions and descriptions primer to my other "Installing Seacocks" article. I'll add this thickness information to the site when I can get it done.. http://upload.pbase.com/edit_gallery/mainecruising/seacock_primer