Through-Hull/Ball Valve Thread Mismatch -- Urban Legend?

[Sailmonkey]

The mismatch isn’t an urban legend when using the US standard npt/nps.

However the rest of the world is built differently.

I’m not a fan of the nut on a mushroom with a valve slapped on top, but do recognize that the majority of boats afloat in this planet are built this way and exhibit no problems.

[Northbound44]

Quick answer about the difference between NPT, BSPP and BSPT:


https://www.ralstoninst.com/news/sto...and-bspt-seals

[boatpoker]

Mainesail's photo .... I know which way I lean.

[Dockhead]

Originally Posted by boatpoker

Mainesail's photo .... I know which way I lean.

That's an NPT/NPS connection. I completely agree it looks bad.


However, a BSPT/BSPP connection looks different:





These are designed to screw together. I guess NPT/NPS are not, so that's probably the reason for the regional differences in practice.

[Dsanduril]

Within the same thread families (at least NPS/NPT with which I am most familiar) the solution is relatively simple. If you have a MS throughull and you wish to attach a FT valve, simply cut the MS portion of the throughull to the desired length and then run a tapered die down the tip of the MS threads. The MS threads have an identical thread-form to the MT, the only difference is the taper itself (again, certain of this for ANSI/US threads, not so much for others simply because I don't know).

I think it may already be linked above but Groco sells throughulls already pre-done with this configuration, MS for the nut attachment to the boat and MT at the inside end for attachment to tapered pipe fittings. But any MS throughull with the proper wall thickness (i.e. wall thickness at least equal to that of the same nominal pipe sizes) can have MT threads put on the end. Since most of our throughulls are bronze the cutting is very easy, probably takes about two minutes. Plastic is a bit more complex, those usually have cast/formed threads and may or may not cut well using standard threading tools.

If you're going down the road of using plumbing fittings attached to throughulls (an entirely different discussion) and you're working in a world with FT as the typically available item (the US at the very least) then I really don't understand why you wouldn't take this simple step. The tools are readily available, and can rented inexpensively if you don't have them.

[waterman46]

Lot of detail here and good to understand, but the "bottom" (no pun intended) line is that in the US at least, your thru-hull fitting has a straight thread and you need to install a true sea-cock on that, not a ball valve. A sea-cock has straight threads on the lower end and a tapered or straight thread (available in either) on the top side.

[Dockhead]

Originally Posted by waterman46

Lot of detail here and good to understand, but the "bottom" (no pun intended) line is that in the US at least, your thru-hull fitting has a straight thread and you need to install a true sea-cock on that, not a ball valve. A sea-cock has straight threads on the lower end and a tapered or straight thread (available in either) on the top side.

Sounds reasonable.


But Groco make a through-hull fitting with combination straight/tapered thread which can have a ball valve screwed directly to it, in case you prefer to do it that way.

[Cadence]

JMHO, mixing a tapered pipe thread and a straight thread in any form of fashion is idiotic.

[Dockhead]

Originally Posted by Cadence

JMHO, mixing a tapered pipe thread and a straight thread in any form of fashion is idiotic.

This is the European standard for mixing tapered and straight:


https://shop.bsigroup.com/ProductDet...00000030235769


It's a specifically approved, specifically designed joint, which has particular advantages over straight/straight and tapered/tapered. It looks like this:





And it's used by the world's finest yacht makers, including Nautor Swan.



Idiotic? Really?

[Cadence]

Originally Posted by Dockhead

This is the European standard for mixing tapered and straight:


https://shop.bsigroup.com/ProductDet...00000030235769


It's a specifically approved, specifically designed joint, which has particular advantages over straight/straight and tapered/tapered. It looks like this:


Attachment 227139


And it's used by the world's finest yacht makers, including Nautor Swan.



Idiotic? Really?

It seem to me both were developed independently.
The more thread contact the better. If not for sealing but the mechanical strength.
As I said JMHO

[Sailor George]

I purchased a 1980 Mariner 36 which was fitted with a taper ball valve on the straight threaded raw water through hull fitting. I was fortunate that I was on the boat when I hit the ball valve and it popped off! Also, lucky that I had wooden tapered bungs to plug the hole! Later, I found out that the ball valve was only screwed with about an 1/8” of threads and pipe sealant was stopping it from leaking. I had the boat hauled out and I replace the through hull with a Garoco Full-Port flanged bronze seacock. It has a female tapered pipe fitting that will accept a marine strainer. It looks and works great after 10 years of constant water contact! In Northern California we only take the boat out every 3 years to paint the bottom. I highly recommend the unit.

[Dockhead]

Originally Posted by Cadence

It seem to me both were developed independently.
The more thread contact the better. If not for sealing but the mechanical strength.
As I said JMHO

No, sorry, BS EN 10226-1 is a specifically designed joint using taper male and straight female. The purpose of it is to allow rotation of the joint, which is impossible with a taper-taper joint. While allowing sealing via threads, which is impossible with a straight-straight joint.


To get more thread contact, you simply design the taper part to fit that far into the straight part -- per the document I linked.

[Cadence]

Originally Posted by Dockhead

No, sorry, BS EN 10226-1 is a specifically designed joint using taper male and straight female. The purpose of it is to allow rotation of the joint, which is impossible with a taper-taper joint. While allowing sealing via threads, which is impossible with a straight-straight joint.


To get more thread contact, you simply design the taper part to fit that far into the straight part -- per the document I linked.

Sorry, I can't see it. Rotation of the joint?

[Joli]

Originally Posted by Dockhead

Quality builders are NOT building underwater fittings with "minimal thread engagement". That is not inherent to MT > FS. This is the EN 10226-1 joint:

Attachment 227098

As you can see, there are standards for thread engagement etc.

This joint has certain advantages over straight to straight or taper to taper. It could be that this clash of consciousness between Americans and Europeans results from BSP threads being specifically designed to be screwed in MT > FS, whereas American standard threads are not designed for this.

From the literature:

"BS EN 10226-1:2004 Pipe threads where pressure tight joints are made on the threads. Taper external threads and parallel internal threads. Dimensions, tolerances and designation
BS EN 10226-1 specifies the requirements for thread form, dimensions, tolerances and designation for jointing pipe threads, sizes 1/16 to 6 inclusive. It applies to joints made pressure tight by means of mating of the threads. These threads are taper external and parallel internal, and are intended for use with pipes suitable for threading and for valves, fittings or other pipeline equipment interconnected by threaded joints.
An appropriate thread sealant or jointing compound should be used on the thread to ensure pressure-tight joints." https://shop.bsigroup.com/ProductDet...00000030235769

I would guess that MT>FS is chosen over MP>FP or MT>FT so that you can have BOTH (1) ability to adjust the angle; AND (2) ability to have watertightness at the threads (with the help of sealant). Only MT>FS will give that.

As to why builders, including all the best yacht builders in the world, choose this method vs "proper sea cocks" -- the answer is NOT that the engineers at Nautor Swan, Oyster, Halberg Rassey, et. al are idiots, or that bean counters at those companies are saving a couple hundred euros on a multi-million euro boat. The answer is that there are different advantages of this construction compared to "proper seacocks" -- fewer holes in the hull meaning less risk of core saturation, leaks, etc.; vastly easier to replace the valve when you need to; simplicity. And done right with proper thread engagement this construction is plenty strong.

I've seen boats where through-hulls were hidden behind cabinetry or equipment; where you couldn't see or reach them; or where on the contrary through-hulls are placed in a position where heavy things can fall on them or you can step on them. I guess you would care more about ultimate strength of the seacock in such cases, but quality builders don't build them like that. In my boat every single underwater through-hull (and there are 15 of them) is located either in the engine room or in a separate compartment which is immediately accessible through a separate hatch and where there is nothing else -- nothing which can fall on them, no way to step on them. The ones in the engine room are right at the doors where they are immediately visible and accessible. It's like this with other quality boats; surely this is much more important than whether the device itself can withstand a 400 pound or a 500 pound side force.

Cutting modified threads is nonsense. Sure you might get a couple more threads to engage but it's still a weak assembly for a critical component. If you're comfortable having less then robust seacocks on your boat that is totally your decision.

We just completed a 1400 mile upwind bash to the Caribbean under triple reefed main and a staysail. I never once thought "gee, I could have saved a couple bucks if I hadn't installed proper seacocks". Not once, when falling of the backs of 20' waves did I wish I had skin fittings with 5 threads of engagement between me and the ocean.

I won't own a boat without proper seacocks.

[Q Xopa]

Originally Posted by Cadence

JMHO, mixing a tapered pipe thread and a straight thread in any form of fashion is idiotic.

Hmmm interestiong and strongly stated opinion.

I am assuming its the tapered threads you dont like?

What is your opinion of what Tapered threads are designed for?

So if I understand your comment correctly you like relying on pipe dope and telfon tape to seal on straight threads, so no actual mechanical metal sealing?