# Installing Seacocks - Follow Up Info !!



## Maine Sail (Jan 6, 2003)

Hi All,

Since posting the article/blog on installing seacocks, seen here, I've had a lot of emails and questions regarding the "mismatching" of different thread types such as NPS and NPT.

A guy on another forum challenged the idea that mismatching threads was OK because "so many do it" so last night I made a cut away view to show why using two different thread types is NOT a good idea. While many boat owners screw NPT threaded valves directly onto NPS threaded through-hull fittings it's clearly NOT a logical idea or even safe as the photo below clearly shows.

To do this 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.

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 fiting 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 an equal resistance.

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 still get two or three full turns out of the NPT nipple.

If you look very closely at the picture you can also see the outer-most threads of the through hull are already NOT fitting tightly against the female threads of the coupling and the inner-most 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 a clear mismatch.

We finally have an answer to this question, with photographic proof, and can clearly see from the photo how dangerous it is to stick an 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 don't do it and do use proper seacocks with bolted flanges..!!

I would have cut away an actual ball valve but I don't have a machine shop. The coupling represents and has the same exact NPT female threads as an in-line valve of either the gate or ball type...


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## brak (Jan 5, 2007)

I am not sure what they say for pipe,but for bolts at least you only need to go in a few thread widths before the connection is considered to have a maximum strength of the fastener.
So, even 4-6 threads may very well be as strong as this connection will ever be.

Of course if you have marine hose above this connection, a failure in hose/clamp area is significantly more likely and going to the expense and difficulty of using flanged thru-hull (not to mention making more holes in the hull for those fastening bolts) may not provide as much safety as desired.


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## KeelHaulin (Mar 7, 2006)

I wonder if a thru-hull that is NPS can be re-cut to NPT on the end since it is already the same thread pitch. I understand what you are pointing out; but many, many boats have ball valves installed onto the thru-hull and there are not lots of reports of boats sinking due to this type of installation.

With a thru-hull that is clamped to the hull via the retaining nut you have lesser chance of the fitting leaking and no extra fasteners penetrating the hull. If a flange mounted seacock leaks you need to pull the boat to fix the leak; with a retaining nut you can attempt to tighten it first. If the thru-hull fitting had NPT re-cut on the end it would be better than a flanged secock (I think).


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## Maine Sail (Jan 6, 2003)

brak said:


> I am not sure what they say for pipe,but for bolts at least you only need to go in a few thread widths before the connection is considered to have a maximum strength of the fastener.
> So, even 4-6 threads may very well be as strong as this connection will ever be.
> 
> Of course if you have marine hose above this connection, a failure in hose/clamp area is significantly more likely and going to the expense and difficulty of using flanged thru-hull (not to mention making more holes in the hull for those fastening bolts) may not provide as much safety as desired.


 Brak,

Your premise & comparison to bolt threads of course does not take into account the improper mismatching of threads that occurs when you screw a valve directly to a through hull. The bolt threads used in your comparison are of the same type. NPS & NPT are two different types of threads and not designed to be used together..


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## Maine Sail (Jan 6, 2003)

KeelHaulin said:


> I wonder if a thru-hull that is NPS can be re-cut to NPT on the end since it is already the same thread pitch. I understand what you are pointing out; but many, many boats have ball valves installed onto the thru-hull and there are not lots of reports of boats sinking due to this type of installation.
> 
> With a thru-hull that is clamped to the hull via the retaining nut you have lesser chance of the fitting leaking and no extra fasteners penetrating the hull. If a flange mounted seacock leaks you need to pull the boat to fix the leak; with a retaining nut you can attempt to tighten it first. If the thru-hull fitting had NPT re-cut on the end it would be better than a flanged secock (I think).


Actually approximately 50% of boat sinking's are as a result of failed below water fittings and a good chunk of this 50% is directly related to failed through hulls or valves as well as hose clamps and hoses. Boats do sink because of improper through hull configurations. A neighbor of mine lost his boat in a lightning strike right in front of our house. Why? Because the few threads holding his gate valve onto his through hull gave way when the current tried to find it's way back to the water. The valve blew right off the through hull. His insurance company tried to decline coverage because the valve was not a marine rated valve and not a proper ABYC or industry installation of a proper seacock. He got a lawyer, fought it and won. The only reason he won was because they had not requested he install proper ABYC or industry accepted seacocks when they examined his initial survey from when he bought the boat..

On my most recent boat purchase (CS-36) my insurance company (Amica) made me replace all my through-hull's w/valves with marine rated seacocks. They did not require, however, that they be through bolted but did require flanges and marine rated. After I installed them, and changed a bunch of other stuff they requested too, such as standing rigging, the surveyor had to come back and sign off. It's getting tougher and tougher to insure an older boat and they are mandating ABYC spec on many items...!

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 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..

P.S. You can have NPS threads cut to what's called a "combination thread" and while still not NPT they are better than stuffing an NPS into an NPT fitting. You will incur machine shop expense or have to custom order the fittings pre-machined that way though and still not have the benefit of the strength of a flanged seacock.


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## TSOJOURNER (Dec 16, 1999)

Is that a brass or bronze pipe nipple? Very important to never use brass on a seawater system.. but seems like you can't find bronze anywhere!
Edit:
Did some quick searching and found that "red brass" sold at marine stores isn't really brass at all



> Gunmetal is a kind of *bronze*, an alloy of copper, tin, and some zinc, originally used chiefly for making guns, but later superseded by steel. It is also *called red brass in America.*
> 
> Gunmetals produced for different purposes vary slightly in composition. In some cases, the alloy may be composed only from copper and tin, or from copper, tin, and lead. It has many uses in industry, and is used for statues and various small objects, e.g. buttons.
> 
> ...


So what gives?? Is "red brass" really bronze and suitable for saltwater application???

Also, regarding proper seacocks (and I DO believe a seacock bolted to the hull is the best way to do it) Nigel Calder has this to say: "At one time the ABYC required seacocks to have flanges that could be securely fasted to the hull. This is no longer part of any standard..."
So, a mushroom with a marine grade valve seems to be acceptable according to Calder. Thoughts?


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## Maine Sail (Jan 6, 2003)

ABYC H-27 was last revised in 1997 but they want $50.00 to download the standard. I don;t know when that Calder book was originally written but my insurance company claimed to be working of ABYC standards and did not want a valve on a through hull..

I'd actually like to know the wording of that standard but not for $50.00..

Oh and yes the nipples are red brass not yellow brass..

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 if your flange-less through hull, with valve screwed onto it, can support a 500lb load test at the outermost fitting I guess your safe?? Mine was hit by an alternator hardly 500lbs..


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## TSOJOURNER (Dec 16, 1999)

For an older boat, with many fittings installed prior to ownership, I always have that feeling "what did they use???"
I had two dangerously corroded GATE valves. One of which the gate was completely missing when I bought my boat. I also have two thruhulls where it is physically impossible to install a seacock. I'm seriously considering the groco NPS-NPT flaged adapter next time I do a serious haulout... It just makes sense to know every 1 1/2" hole is backed up with something substantial.

Those thoughts aside, I neglected to properly cite my Calder quote above. That is from "Boatowner's Mechanical and Electrical Manual," 3rd ed., 2005. In that book he does detail the rigorous testing that seacocks and thruhulls must endure. Lets just say I'm not willing to perform those same tests on my boat while in the water

500lbs alternator??


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## steelboat (Dec 28, 2007)

In my opinion, Halekai 36 is entirely correct in his assertment that you should not interchange NPS with NPT threads. I have some machining experience, (I have a Bridgeport at my house) and while it may be possible in some cases to re-machine one part to match the other, why would you do this when you can buy the correct stuff in the first place? If you want to hear horror stories about mis-matched thru hulls and sea cocks, call Groco direct and speak to one of the thru hull techs on this subject... they're pretty passionate about it and can tell quite a few stories of new boat sinkings, law suits, etc.


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## TSOJOURNER (Dec 16, 1999)

steelboat said:


> they're pretty passionate about it and can tell quite a few stories of new boat sinkings, law suits, etc.


While your on the phone ask them about their latest product recall too.


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## steelboat (Dec 28, 2007)

Yeah, it's true they do have a minor technical problem with their recall, don't they? I'm sure a lot of people are not happy about that, and justifiably so. But the fact remains that NPT and NPS don't mix.


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## brak (Jan 5, 2007)

I am sure flanged thru-hulls bolted to the hull are stronger, but I am not convinced that seacock on the thru-hull would fail the load test. If this is the case - most production sailboats are not made to the ABYC spec, as they commonly use exactly such a set up. 

Another thing to consider - bronze is fairly pliable, and with enough torque one could get quite a few more turns even when using straight thread with the NPT female part. 

BTW, how do they create a load in the proposed load test? Is it a top load? From outside inward? Side/sheer?


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## Maine Sail (Jan 6, 2003)

sailboy21 said:


> While your on the phone ask them about their latest product recall too.


I have done just that! When I called Groco & spoke with Jamie P., who is very well versed by the way, I was told that the new valves stems are indeed bronze not yellow brass and that is apparently a typo. They meant brass in color. However, it they ever do fail, I can easily replace them because I used the flanged adapter not the integral valve as in the pictures.

The recall of these valves was NOT for corrosion issues, as many forum goers have so incorrectly assumed, but rather because the manufacturing factory changed spec on Groco, without telling them, then could not guarantee the quality of or even give specs on what type of stainless the stems were made of. According to Groco most of these valves went to a select few OEM's most of them in Florida. By the way the balls in the Groco valves are plated red brass not yellow brass...

Oh, and I still think I'd rather have the Groco's over the the failures I've had with Marelon which by the way Forespar/RC Marine NEVER recalled or admitted there was even a problem. At least Groco tries to address an issue which is more than I can say for RC/Forespar..!!


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## Maine Sail (Jan 6, 2003)

brak said:


> I am sure flanged thru-hulls bolted to the hull are stronger, but I am not convinced that seacock on the thru-hull would fail the load test. If this is the case - most production sailboats are not made to the ABYC spec, as they commonly use exactly such a set up.
> 
> Another thing to consider - bronze is fairly pliable, and with enough torque one could get quite a few more turns even when using straight thread with the NPT female part.
> 
> BTW, how do they create a load in the proposed load test? Is it a top load? From outside inward? Side/sheer?


It's a side load for ABYC H-27 ..

Bronze is pliable? Have you ever worked with it? Perhaps you're thinking of yellow brass.. By the way even Catalina is using flanged Marelon seacocks thee days...


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## brak (Jan 5, 2007)

halekai36 said:


> The recall of these valves was NOT for corrosion issues, as many forum goers have so incorrectly assumed, but rather because the manufacturing factory changed spec on Groco, without telling them, then could not guarantee the quality of or even give specs on what type of stainless the stems were made of. According to Groco most of these valves went to a select few OEM's most of them in Florida. By the way the balls in the Groco valves are plated red brass not yellow brass...


Well, I understand that at this point this is just a "spec" issue, but reality of the matter is - the manufacturer probably substituted a substandard steel and it will corrode faster than proper stainless would have, so it is just a question of time.

I asked this in another thread but I'll reask here - "valve stem" refers to the pin on which the actual ball and the handle turn? I suppose thats all it could be, in which case I am screwed - every single one of the valves I installed has that in steel, and I installed them all last August, so they are well within the recall timeframe.

Guess that means haulout this year which I wasn't even planning on until now  Another day, another thousand $$$.


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## steelboat (Dec 28, 2007)

Brak: yes, valve stem refers to the piece that connects the ball and handle... actually, you may be all right, depending on when you actually bought the valves, or, more appropriately I guess, when they were made, because Groco says in a service bulletin on their web site that they're talking about valves manufactured between 2004-2006. If you installed them in August 2007, they may have been made in 2007, so you might luck out. Bob


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## brak (Jan 5, 2007)

Well, since I have no way to check that - I would have to either wait till they rust and fail or replace them anyway. I bought them at Hamilton marine, and by the looks of it those guys stock valves for a long long time.

This is the second time in a year (and the same refit) that cheap chinese metal screws me up (the previous was brand new turnbuckle that failed and almost cost me a mast, I wrote about it here). If things continue that way I better sell my boat before all these "new" components start failing


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## sailingdog (Mar 19, 2006)

Halekai-

Thanks for the work and the photos. 

If you think about it... it really makes sense that the through hull has to be NPS. If it was NPT, then you couldn't cut it to the proper length, since the threads would be tapered. 

However, it makes sense that the rest of the pipes are NPT, since NPT joins seal much better, since they're tapered.


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## KeelHaulin (Mar 7, 2006)

halekai36 said:


> Actually approximately 50% of boat sinking's are as a result of failed below water fittings and a good chunk of this 50% is directly related to failed through hulls or valves as well as hose clamps and hoses. Boats do sink because of improper through hull configurations. A neighbor of mine lost his boat in a lightning strike right in front of our house. Why? Because the few threads holding his gate valve onto his through hull gave way when the current tried to find it's way back to the water. The valve blew right off the through hull.


Yes; but the major reason that these failures occur is lack of maintenance, visual inspection, or no valve on the thru-hull. You can't just say that because 50% of sinkings are due to failed below waterline connections that it is all due to this NPS/NPT issue.

The load requirement of 500# lateral load is not very big. I'm sure that most thru-hull fittings will pass this; nowadays they are using marelon valves on top of marelon fittings (non NPT) and passing the 500# load req.

On the issue of your friend's boat sinking due to the thru hull failure, I'm sorry it happened to him. But I completely disagree with the premise that the failure of the thru hull was due to poor electrical connection at the valve threads. The boat sank due to a lightning strike; that's all. The boat did not have an adequate lightning protection system to route the electricity to the keel or grounding plate and the result was a melted thru-hull. Lightning can burn a hole directly through the fiberglass. If it did not have the pathway through the thru-hull it would have went through the hull itself. The failure of the seacock at it's connections is just due to the immense current (several million amps) and no seacock/thru-hull connection is designed to take that much current without melting or melting the surrounding plastic.



> 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 and I found the problem in time, thank god for bilge alarms, but I could have lost it.


Again sorry to hear this; but the problem is not due to the valve being sub-standard. A 20# alternator traveling at ~10 feet second is going to generate an impact force that is greater than 500#. Remember that the load requirement is for 500# of _static_ load. If you throw a bowling ball at the top of the seacock you will put several thousand pounds of impact force on it. This is a reminder for us all to be sure that nothing heavy can fall against a thru-hull fitting regardless of how it is attached to the hull.(including items that -should- be secured like water tanks). Keep heavy objects out of lockers that contain the thru-hull fittings; this will minimize any chance of failure due to an external force on the fitting.



> You will incur machine shop expense or have to custom order the fittings pre-machined that way though and still not have the benefit of the strength of a flanged seacock.


No; I was thinking more along the lines of tapping the thread with an NPT die either on the bench or when the fitting is installed onto the hull (if access is good). Seems like it would be easy enough to re-cut a taper onto the existing threads because most of the thread forming is done already.

My question is if bolting the thru-hull to the hull with the clamping nut is not acceptable; why do they sell the clamping nut with the fitting? Once the nut is secured there is no other way to attach a fitting or valve unless it is threaded NPS (which you can't find).


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## Sapperwhite (Oct 21, 2006)

steelboat said:


> Yeah, it's true they do have a minor technical problem with their recall, don't they? I'm sure a lot of people are not happy about that, and justifiably so. But the fact remains that NPT and NPS don't mix.


Halekai, good work again. As steeboat points out, NPT and NPS don't mix. I am having trouble understanding the arguement/discussion/whatever that is going on here. Why buy and then attempt to modify the wrong component when the right component is available? I can understand (almost) if you are half way around the world and resources are limited, but thats not the case. Also, I don't get the "good enough" attitude about having what looks like enough thread, particularly when Halekais demonstration shows what can be achieved with the correct fitting.


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## Maine Sail (Jan 6, 2003)

KeelHaulin said:


> Yes; but the major reason that these failures occur is lack of maintenance, visual inspection, or no valve on the thru-hull. You can't just say that because 50% of sinkings are due to failed below waterline connections that it is all due to this NPS/NPT issue.


I NEVER said that ALL 50% were due to NPS or NPT failures. In fact in that statement I never mentioned NPT or NPS and did reference thru-hulls, hose clamps and hoses.

Here's what I actually said:
_"Actually approximately 50% of boat sinking's are as a result of failed below water fittings and a good chunk of this 50% is directly related to failed through hulls or valves as well as hose clamps and hoses."_

I try an contribute here with information that may be valid for some and many do appreciate the information I bring to the table. If you don't agree with what I've discovered or posted that's fine and we can debate the pro's and con's all day long, if you want to, but please don't try and put words on my mouth or misquote me. That's all I ask an it's only fair..

It's all there in black & white and I never said:
_"You can't just say that because 50% of sinkings are due to failed below waterline connections that it is all due to this NPS/NPT issue."_

My alternator weighed 12lbs, not 20, I know because I sold that spare after selling that boat and I agreed to pay the shipping for the buyer. I have no idea what the velocity was but it was stored less than 14 inches from the through hull and wrapped in plastic and bubble wrap with silica packets in side to keep it fresh.

I don't know what all manufacturers are doing with Marelon but Catalina and many of the fishing boats I've seen use Marelon flanged seacocks (NPS) and marelon thru-hulls also NPS.

I know many boats, in the thousands, 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.


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## brak (Jan 5, 2007)

KeelHaulin said:


> My question is if bolting the thru-hull to the hull with the clamping nut is not acceptable; why do they sell the clamping nut with the fitting? Once the nut is secured there is no other way to attach a fitting or valve unless it is threaded NPS (which you can't find).


Actually, there can't be screw on valves or fittings with NPS thread because NPS thread has no sealing mechanism (and no amount of telfon will seal it) - straight thread is just that, it allows water to seep through the thread. NPT seals by virtue of having the taper in threads which works by squeezing metal vs. metal until threads further in are completely locked and water or whatever else tight.

When using flanged seacocks, water is sealed by essentially gluing the seacock flange to the hull. It seeps backwards easily through straight NPS thread and gets blocked by flange seal. BTW, in that sort of installation sealant becomes critical. Moreover, using wood block as a backing plate for the thru-hull will pretty much guarantee that water from straight thread will get to it (and rot it eventually). Also, since the entire surface of the threaded connection is accessible to water (unlike NPT where from some point in the threaded connection water is blocked) I wonder how that affects corrosion and connection strength.


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## TSOJOURNER (Dec 16, 1999)

brak said:


> Actually, there can't be screw on valves or fittings with NPS thread because NPS thread has no sealing mechanism (and no amount of telfon will seal it) - straight thread is just that, it allows water to seep through the thread. NPT seals by virtue of having the taper in threads which works by squeezing metal vs. metal until threads further in are completely locked and water or whatever else tight.


You can seal just about anything with the right product


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## KeelHaulin (Mar 7, 2006)

I was not trying to put words in your mouth halekai; it seemed to me when I read your post that you were pointing out that this particular issue is a major problem (in numbers/percentages) when we don't actually know this to be true.

When a boat is constructed with seacocks that are not mounted flush to the hull it can be a real bugger to retrofit them to the "correct" type because of limited access and the need to get a flush/square surface at the attachment point. That's why I am putting out the suggestion that cutting a taper onto a new or existing (good) thru-hull might be a good option should you feel the need to have tapered threads on both the valve and the thru-hull. In the overall job it might be worth cutting the threads onto the thru-hull to save the expense/difficulty of retrofitting.

It's too bad that the ends of the thru-hulls are not tapered to begin with; it would work fine in the event that you need to cut them shorter for a flush mount (you'd just cut the taper off).

Hmm... I don't think I would like to buy an alternator that had knocked the thru hull valve off and had sea water flooding into it's compartment. I guess that's why "used gear" is generally much lower in price compared to new.


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## Maine Sail (Jan 6, 2003)

KeelHaulin said:


> Hmm... I don't think I would like to buy an alternator that had knocked the thru hull valve off and had sea water flooding into it's compartment. I guess that's why "used gear" is generally much lower in price compared to new.


The alternator was fine and as I stated above it was wrapped in plastic with silica packets and sealed to keep it's inner windings free of corrosion. Only the outer plastic got wet and a couple of small paint chips in the casing were all that was visible. Plus I had the unit bench tested before selling it. It only ever had 10 hours of use and I sold it for $125.00 shipped. All in all for a couple of paint chips the guy got a heck of a good deal considering it was a $533.72 unit as seen here: Universal 51 amp alternator for M3-20B


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## Maine Sail (Jan 6, 2003)

KeelHaulin said:


> When a boat is constructed with seacocks that are not mounted flush to the hull it can be a real bugger to retrofit them to the "correct" type because of limited access and the need to get a flush/square surface at the attachment point.


This system works well for the situation you describe. It's nice and low with a replaceable valve, bonding screw, properly matched threads and a flange:









And it fit in this very low profile bilge area with a solid fiberglass 5/8" backing plate. Retrofitting for the ultimate strength and safety can almost always be achieved if one so desires..


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## Faster (Sep 13, 2005)

Excellent presentation and documentation, Halekai.

It brings up the question: Why aren't through hull fittings manufactured with an NPS section for the clamp nut, and the last inch (or whatever's required for fit) in NPT? Do you think that the end of a standard NPS throughhull could be re-threaded to NPT without losing too much wall thickness?

I suppose the shorter "NPS" section might be a limiting factor in particularly thick hulls, but for most applications such a fitting should serve well...


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## TSOJOURNER (Dec 16, 1999)

Faster said:


> Excellent presentation and documentation, Halekai.
> 
> It brings up the question: Why aren't through hull fittings manufactured with an NPS section for the clamp nut, and the last inch (or whatever's required for fit) in NPT? Do you think that the end of a standard NPS throughhull could be re-threaded to NPT without losing too much wall thickness?
> 
> I suppose the shorter "NPS" section might be a limiting factor in particularly thick hulls, but for most applications such a fitting should serve well...


I've seen pipe threading kits on ebay for $20 that can do 1 1/4" 
That would be an interesting experiment..take some measurements, compare the groco flange adapter.. might be compelling. 
Then do the 500lb weight test.


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## Maine Sail (Jan 6, 2003)

*You wanted measurements.!*

You wanted measurements here they are:

*Total thickness of a 1" bronze through hull 2.99mm*








*Now subtract the dept of the treads cut into it @ 1.45mm*
















*2.99mm minus 1.45mm is 1.54mm nominal wall thickness for a 1" thru-hull*








*Yes this Penny is actually thicker than the cross section of this 1" thru-hull*
*Not a lot of meat between your boat and the bottom of the ocean!*


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## brak (Jan 5, 2007)

Halekai, you really are fudging the numbers now. The depth of the thread is less, the thickness of the wall is more and penny is less (20 pennies are an inch thick, so a penny is more like 1.2mm)

More importantly, hardness of decent bronze alloy is something like 300mPa or 43000lbs/sq.in, tensile strength is double that. Even assuming that cros-section of that pipe is only 1/10 of a square inch (which would be the case with 1mm wall tickness) we are talking of 4000lbs or more required to make any impact on that pipe.



halekai36 said:


> You wanted measurements here they are:
> 
> *Total thickness of a 1" bronze through hull 2.99mm*
> 
> ...


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## Maine Sail (Jan 6, 2003)

*Now for the flange.*

*Now for the flange. Let's compare the nominal wall thickness of a proper flange to the thru-hull fitting pictured above:*
*
Outside total width of the flange = 35.33mm*








*Inside width, thread to thread, measures 24.16mm*









*Now do the math 35.33mm minus 24.16mm =11.17mm divided by 2 = 5.58mm minus the thread depth of 1.26mm = 4.32mm nominal wall thickness*
*
So, it looks as if a flanged adapter plate, at 4.32mm, is 2.8 times the thickness of the above pictured thru-hull fitting at 1.54mm.

I know which set up I'm using on my boat and it's not the one that has a wall thickness of roughly one penny's width!!!*

(In the interest of full disclosure this was edited to reflect the actual measured thread depth of the 3/4 inch fitting not the 1" fitting which I originally assumed incorrectly, would be the same, from the 1" fitting to the 3/4 inch flange. The difference is very small .19mm but I wanted to be as accurate as possible.)


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## brak (Jan 5, 2007)

Conbraco spec shows wall thickness of 4.86mm for thru-hulls of 1/2" to 1" diameter.


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## Maine Sail (Jan 6, 2003)

brak said:


> Conbraco spec shows wall thickness of 4.86mm for thru-hulls of 1/2" to 1" diameter.


Well considering Conbraco is Apollo it's fairly clear their specs are WAY, WAY off because the thru-hull in the photos is an Apollo purchased this past Thursday at Hamilton Marine!! The pictures DON'T lie and I zero'd my calipers before each measurement was taken!

I just searched for quite some time on the Conbraco site and found every spec but nominal wall thickness of their thru-hulls. Brak, can you please post a link to that info so I can actually see it. If it is true, and there in black and white, I will then forward my photos to them and ask them to update their literature to be more closely reflective of the product they are actually shipping.

My guess, if that spec is there, is that they are measuring before the threads have even been cut into it.

Most thru-hulls are built to satisfy the "full port spec" so I doubt you'll see a great variance in total thickness but anything is possible as Conbraco is saying over 4mm in thickness? I also have a Perko through hull and it too measured in very, very close to the Apollo. I'd be very curious to know when they, as in Conbraco, took that stat before or after the threads were cut...?? Heck this could be another case of the Chinese changing spec again....


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## brak (Jan 5, 2007)

Search for the strainer thru-hull (that's the one I found) from marine product menu on the main page. Technical spec (one of the links on the right hand side) has thickness of material. It is measured on another edge of the thru-hull (outside edge) but I measured the drawing and thickness of that part is the same as thickness of the top part, so assuming that drawing is correct and to scale - that is the number. It is the thickness including thread, so you do need to subtract thread depth for actual wall.


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## Maine Sail (Jan 6, 2003)

brak said:


> Halekai, you really are fudging the numbers now. The depth of the thread is less, the thickness of the wall is more and penny is less (20 pennies are an inch thick, so a penny is more like 1.2mm)
> 
> More importantly, hardness of decent bronze alloy is something like 300mPa or 43000lbs/sq.in, tensile strength is double that. Even assuming that cros-section of that pipe is only 1/10 of a square inch (which would be the case with 1mm wall tickness) we are talking of 4000lbs or more required to make any impact on that pipe.


Brak,

Sorry Brak there was no fudging of numbers & my calipers were zero'd each time and are very, very accurate. Look closely the calipers are HOLDING the penny and it's not falling out. They were also holding themselves while I took the picture of them measuring the threads. I achieved this by clamping them down then locking them in place with the locking knob so I could snap the shot.

Brak, if you're calling me a liar I feel terribly sorry for you. I challenge you to buy a good set of calipers and do this experiment yourself. That's a bold statement on your part when you can clearly see the calipers clamped tightly in each photo. You can see higher resolution photos, to do your best Matlock impersonation on, here.

If you want bigger photos on my site just click them.

By the way, after your very scientific accusations of _"20 pennies are an inch thick, so a penny is more like 1.2mm"_ I re-measured a few pennies and I was surprised to find out that pennies actually range some in thickness. The first one I grabbed for those photos was 1.57mm. Some measured close to 1.58 and some measured closer to 1.51.

Of course I'm sure you know that tensile strength and sheer strength are two different things.....

One thing that we do know for sure is that a flange, as in the one pictured above, is MUCH, MUCH more robust in strength than a thru-hull fitting alone..

*Silicon Bronze CA655 *
Nonferrous alloy -1/2 hard ca 655 (high silicon bronze) is a hard - high strength alloy with excellent corrosion resistance.
It is typically used for marine hardware, nuts, bolts, screws, propeller shafts, bushings, chemical equipment & shafting etc.
Capacity for being cold worked & hot formed is excellent.
Machine-ability rating (ca360 = 100) is 30.
Tensile strength 78ksi Yield strength 45ksi, Elongation 35, Rockwell Hardness = 85B shear strength = 52 ksi.



brak said:


> Search for the strainer thru-hull (that's the one I found) from marine product menu on the main page. Technical spec (one of the links on the right hand side) has thickness of material. It is measured on another edge of the thru-hull (outside edge) but I measured the drawing and thickness of that part is the same as thickness of the top part, so assuming that drawing is correct and to scale - that is the number. It is the thickness including thread, so you do need to subtract thread depth for actual wall.


So your "data" comes from measuring a printed out line drawing and they don't actually give the wall thickness on the web site as I found out........ Nice!!!!

Brak,

As I've stated before use what you feel comfortable with. Many insurance companies, thru-hull manufacturers, surveyors and boat builders don't feel comfortable with a ball valve threaded directly to a flange less thru-hull with mismatched threads so I'm not alone on this issue. I'm merely providing some data that has never been looked at or shown in photographs as far as I know of..


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## TSOJOURNER (Dec 16, 1999)

halekai36 said:


> *Now for the flange. Let's compare the nominal wall thickness of a proper flange to the thru-hull fitting pictured above:
> 
> Outside total width of the flange = 35.33mm
> 
> ...


But isn't wall thickness = OD-ID / 2? 4.86mm?

So.. Assuming a thruhull is at least as thick as a regular pipe nipple:
Schedule 40 1" nominal:
OD ID Wall Thickness
1.315" 1.049" 0.133"
33.4mm 26.6mm *3.38*mm

60 degree 11.5 thread/per inch Threads will cut about 1.9mm, so you should still have *1.48*mm.
With your measured thread depth 1.45mm we get 1.93mm, still a decent amount of bronze. OD and ID of the thruhull would be useful in comparison. I'll take a trip to the local WM to see how consistent these things are.

What is the wall thickness at the NPT end of the flange adapter?

Thanks for the very descriptive and detailed illustration. Saving a lot of us a lot of time next haulout 

Whats with the metric?? NPS, NPT, thats English..


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## sailingdog (Mar 19, 2006)

Halekai-

Brak's got a good point... you forgot to divide by two, since the difference is for both sides of the through-hull. So the actual solid wall thickness is (11.17 mm / 2)-1.45 mm... or 4.135 mm, which is only 2.68 times the thickness. 

However, that is just a base measurement and doesn't take into account the flange's much greater ability to resist lateral stresses due to the support provided by the flange's surface area and the fact that it is through-bolted to the hull.


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## Maine Sail (Jan 6, 2003)

sailboy21 said:


> But isn't wall thickness = OD-ID / 2? 4.86mm?


Yes my bad it was late! Sorry for the dumb blond/blonde moment!! Still it's more than twice as thick...

P.S. I corrected my "fuzzy math" on both my web site and the posts above for future readers! Thanks to Sailboy21 for picking p on that!!


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## sailingdog (Mar 19, 2006)

The photos are excellent, as always... suggest drinking more coffee before tackling the math part next time.


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## Maine Sail (Jan 6, 2003)

sailboy21 said:


> What is the wall thickness at the NPT end of the flange adapter?
> 
> Thanks for the very descriptive and detailed illustration. Saving a lot of us a lot of time next haulout
> 
> Whats with the metric?? NPS, NPT, thats English..


I left my calipers in metric to make the basic math easier for those who don't like fractions. I feel when measuring something this small using millimeters is just easier..

Here you go:

In the interest of fairness I also wanted to measure the total wall thickness of the flange, at the top threads, to compare it to the 1" thru-hull nominal wall thickness. I understand I'm not comparing two 1" or two 3/4 inch fittings but the points remain the same and the wall thickness is what I am trying to get at. This fitting measured an overall thickness of 4.04 millimeters and a thread depth of 1.26 millimeters (I made another mistake above assuming 3/4 inch threads were the same depth as 1" which I have fixed). When you subtract 1.26 from 4.04 you are left with a total nominal wall thickness of 2.78. This makes the thickness, of this flanged 3/4 inch fitting, at the top NPT threads, approximately 1.8 times thicker than those of the 1" thru-hull or roughly two pennies thickness vs. one..

P.S. Measuring thread depth on these smaller threads was difficult and there could be a slight variance but I would not guess it to be any more than +/- .05 which really does not make that much difference in the big picture.

Overall Thickness:








3/4 Inch Thread Depth:


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## KeelHaulin (Mar 7, 2006)

Faster said:


> It brings up the question: Why aren't through hull fittings manufactured with an NPS section for the clamp nut, and the last inch (or whatever's required for fit) in NPT? Do you think that the end of a standard NPS throughhull could be re-threaded to NPT without losing too much wall thickness?


That's precisely the suggestion that I was trying to make earlier...

Older thru-hull fittings are much thicker than the new ones; might be worth re-threading an older unit that is fine otherwise. When I replaced 3 of the thru-hulls on my boat I found that the old units were much heavier gauge and had no corrosion of the threads other than surface oxidation. The new thru hulls weighed 1/2 as much as the old ones mostly due to thinner wall thickness. Still; a new bronze thru hull is going to be much stronger than a plastic one.

JMHO...


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## Maine Sail (Jan 6, 2003)

*Guys...*

Guys....

My thru-hull that broke was indeed old although not original as Catalina used to glass pipe nipples into the hull and this was a standard bronze thru-hull and not a pipe nipple. At the time I really didn't care, or have a digital camera, and just wanted it out of the boat so I really did not examine it too closely but nothing else on that boat was suffering from corrosion but I can't honestly confirm that this thru-hull was not corroded because at the time I just wanted to fix the boat and could have cared less.

Part of the problem, contrubuting to my cracked thru-hull, was perhaps the height of the valve and hose barb? Who ever installed the thru-hull, before me, never cut it down to reduce the height then obviously threaded a valve and a hose barb onto it as well.

My guess is that the alternator hit it fairly high (more leverage). I was actually able to back the valve off once the boat was out of the water and that did not break it any further but I could not back the big nut off because the through hull threads had been damaged. I wound up having to use a 4" angle grinder to grind the mushroom head off the push the whole thing back into the boat..

On another note I wanted to post some pricing and really ask the question of why someone would go to extreme lengths & measures, such as re-cutting the threads, which I think we can all agree is not as strong as a proper seacock?

All marine prices are from Hamilton Marine except the pipe threading die.

1" Ridgid Pipe Die (just the die) $98.00 (see link here)
1" Thru-hull fitting 15.99 (needed for either installation)
1" Bronze Marine ball valve $29.99 (for valve to thru-hull installation only)
1" Bronze "proper" seacock $51.99

So to install it the "weaker way" and thread a ball valve directly onto a thru-hull fitting but re-cut the threads the cost is:

_Thru-hull @ $15.99 + ball valve @ 29.99 + Die @ $98.00 ($98.00 is bare minimum and assumes you already have a ratcheting die handle to fit the die head)._

The total cost for these parts is $143.98. Of course if you have more than one 1" thru-hull you can amortize the cost of the die across a few valves but if you have different sizes you'll need a die for each. Still, in the end, this is a much weaker design than a flanged seacock.

To do it the "proper" way with a flanged seacock the cost is this:

_Thru-hull @ $15.99 + 1" seacock @ $51.99 + three bronze bolts w/ nuts and washers @ $3.76._

The total parts cost for this installation is $71.74 or $72.74 LESS than installing a ball valve directly on a thru-hull and re-cutting the threads with a $98.00 die.

*Let's say for the sake of it we don't re-cut the threads. The total parts cost difference is still only $22.00 to do it the "proper" way! *

So, if I understand the logic of some, we spend tens of thousands of dollars on a boat and we're taking a short cut on something as important as a hole in the hull that could potentially sink your boat. We're actually debating over a $22.00 price difference between a 1" bronze ball valve @ $29.99 and a bronze seacock @ $51.99...

*I am in no way inferring anyone with valves mounted directly to a through hull should run out and change them if they are not leaking or severely corroded! I'm merely suggesting that when you do decide to install new thru-hulls and valves to consider the safer method of a flanged seacock.

Forget about the through-bolting part for now because even a flanged seacock, that is wood screwed, or tapped to potted holes or a fiberglass backing plate will be considerably safer & stronger than a valve screwed onto a thru-hull regardless of the threads matching or not.*

Again, you guys can do what you want with your own five or six figure boats & I'll spend the extra $22.00 and sleep well......... Don't kill the messenger...!!


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## KeelHaulin (Mar 7, 2006)

You know... There is such a thing as differing opinions halekai. If there were not we would not be discussing these things in a forum we would just be doing our own thing. You must realize that in certain situations it is just not feasible to do what you are trying to say is "required" for a safe/seaworthy connection. 

On my boat the original thru-hulls were flush/recessed fittings. On the interior the 1" thick hull is raised above the surrounding hull (to maintain hull thickness at the fitting) and flat where the backing block meets the hull. A sea-cock style fitting won't work because the raised pad is not big enough to accomodate the diameter of the thru-bolt hole pattern. 

So I'm supposed to grind my hull thinner to install a thru-bolted seacock so that I can "comply" with an unwritten requirement? Sorry; ain't gonna happen. The boat has been fine for the last 25+ years so that's enough proof (to me) that the valve connections are not going to fail. When I removed one of the fittings (the most corroded looking) I kicked myself for ruining the threads while pounding it out from the hull; it was much heavier/stronger than the new one that went in it's place.

The valves on my boat are located in areas where I don't need to stow heavy items. I don't intend to store items that would cause damage to the thru hull in those locations; so by design they are protected from heavy impact damage. I will give them a whack with a mallot when hauled to check for strength of the thru-hull but I don't think I will be replacing any them unless the valve requires servicing, or there is a leak. I don't consider adding 3 holes per thru hull into the bottom of the boat "a better way" if it really is not needed anyway...

Nice job with articles on your website BTW.

JMHO/FWIW....


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## Maine Sail (Jan 6, 2003)

*And..*



KeelHaulin said:


> You know... There is such a thing as differing opinions halekai. If there were not we would not be discussing these things in a forum we would just be doing our own thing. You must realize that in certain situations it is just not feasible to do what you are trying to say is "required" for a safe/seaworthy connection.
> 
> On my boat the original thru-hulls were flush/recessed fittings. On the interior the 1" thick hull is raised above the surrounding hull (to maintain hull thickness at the fitting) and flat where the backing block meets the hull. A sea-cock style fitting won't work because the raised pad is not big enough to accomodate the diameter of the thru-bolt hole pattern.
> 
> ...


That's why I say: _*"I'm merely suggesting that when you do decide to install new thru-hulls and valves to consider the safer method of a flanged seacock." 
*_
Consider is the key word there.. _*
*_


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## TSOJOURNER (Dec 16, 1999)

halekai36 said:


> Guys....
> My thru-hull that broke was indeed old although not original as Catalina used to glass pipe nipples into the hull and this was a


Yeah.. about those. Whose idea was that? They didn't know back then that glass wouldn't hold a permanent bond to a freaking pipe nipple? Any builder that did that needs a slap across the face.
That said, ONE of my thruhulls is still a pipe nipple style. It is a 1 1/4" cockpit drain. Should that be a priority? Can't really do anything until spring since glass won't cure at 35 degress  Nice thing about living in AK is there is sometimes 12-14foot tides. The city run tide grid charges $10/day. Pretty economical way to do things.. just make sure everything is set and curred before the tide comes back!


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## TSOJOURNER (Dec 16, 1999)

halekai36 said:


> You wanted measurements here they are:
> 
> *Total thickness of a 1" bronze through hull 2.99mm*
> 
> ...


In the interest of science I decided to test this conclusion. My procedure was slightly different, but same as yours for the groco flange. Here are my results:

Sample:1" "Apollo" bronze thruhull
Nominal OD: 1.29"
Threads: 11.5 / inch​Measurements:









Measured from maximum cut in threads 180 degrees. I choose this method using the knife edge portion of the caliper since I feel it gives a better measurement that the depth gauge part. The depth gage is thicker, and did not extend to the absolute maximum cut, as the knife edge did.

















Calculations:
Wall Thickness = (OD - ID) / 2
Wall thickness before threads were cut:
1.289-1.036 / 2 = .127" (3.23mm)​Wall thickness from maximum thread depth:Compensate for angularity of the OD measurement:
Thread Pitch = 1/11.5 = .087"
1/2 pitch = .043"
Measured OD = 1.203 therefore actual OD = SQRT(1.203² - .043²) = 1.202"​1.202 - 1.036 / 2 = .084" (2.12mm)​My penny was 1.48mm 
All calculations were carried out on excel, therefore no rounding was used during the calculations.

Over a range of sizes:








In the screenshot "ID Corr" should read "OD Corr"

So, in conclusion, my random (it was the only 1 one stock) sample had a .67mm thicker final wall thickness. 
Since these are cast, and subject to variation, my suggestion is take a caliper to the store to make sure you get the most bang for the buck.
I wonder what kind of quality control is in place at the factory?


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## Maine Sail (Jan 6, 2003)

sailboy21 said:


> I wonder what kind of quality control is in place at the factory?


My guess is multiple vendors/suppliers. It's very interesting that your 1" sample was slightly thicker than mine, although using a slightly different method, but your penny was thinner.

I measured about 10 pennies during this process and each one was slightly different. Heck if the US mint can't get the nominal thickness of our currency standardized we certainly can't expect Apollo to be consistent with cast bronze thru-hulls! The bottom line is these things are still quite thin! Your 2.1mm is not much of a wall nor is my 1.5mm measurement for a 1" thru=hull...

P.S. My knife edges would not totally bottom out into the valley of the threads so I unfortunately could not measure using that method with accuracy even though that was my first choice..


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## brak (Jan 5, 2007)

So - two things.

First, I just inspected all my GRACO ball valves, and all have "brass" (yellow) stems - so I am off the hook for the recall. Yee-haw!

Secondly, I looked at a few thru-hulls available at local Boaters World and didn't need a micrometer to tell that they were much thinner than those I installed. They also had hole not quite in the center, making walls thinner in some places than others. I've seen the same before and it does seem to support the idea that there are different suppliers and quality control is probably not there.


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## TSOJOURNER (Dec 16, 1999)

halekai36 said:


> I measured about 10 pennies during this process and each one was slightly different. Heck if the US mint can't get the nominal thickness of our currency standardized we certainly can't expect Apollo to be consistent with cast bronze thru-hulls! .


To be fair to the US mint, the penny has gone through many changes and material compositions, and are minted at (5?) different mints. The penny on my desk was from 1962, no doubt the edges had been rounded, corrosion, sheesh.. how many washing machine cycles had the poor thing been through? Probably has even done more sea miles than a good bit of us!


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