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Old 20-05-2013, 12:59   #16
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Originally Posted by goboatingnow View Post

A proper unibody seacock is of course better, but the Groco flange adaptor which solved the NPS to NPT issue with threads, in my view doesnt add any appreciable additional strength. You clearly still have a threaded tube exiting the flange to take the ball valve and Maine sails video show the interface that the failure occurs in, is that thread area ( which is self explanatory as thats where the weak point is).

A properly support thru hull, with significant bearing face height and where the valve is close to the flange nut ( ie reducing the lever moment) is likely to be more then sufficiently strong in comparison.

What the Groco adaptor does ( which is why its called an adaptor) is to handle the issue of parallel to taper threads issue , that is a problem ( well sort of ) with parallel through hulls and parallel threaded valves.

dave
When you bolt down the flange of either a flanged seacock or the flanged adapter, you transfer any side loading to the flange and it's bolts, which can take it. When you screw a valve onto a thru-hull fitting, any side loading is transferred to that weak thru hull fitting.
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Old 20-05-2013, 13:07   #17
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Re: Aligning plumbing fitttings

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Originally Posted by s/v Jedi View Post
When you bolt down the flange of either a flanged seacock or the flanged adapter, you transfer any side loading to the flange and it's bolts, which can take it. When you screw a valve onto a thru-hull fitting, any side loading is transferred to that weak thru hull fitting.
I fail to see how the male threads of a flanged adaptor provide any more strength then then threads of a through hull , that is properly supported by the correct backing pad thickness and where the tru- hull is then cut to the correct length. MaineSails video clearly demonstrates that the thread fails at the top of the flanged nut, hence it would also fail at the top of the Groco adaptor where the male thread begins, as that is the weakest point.


Unibody flanged seacocks, yes they are different, there is no intervening thread
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Old 20-05-2013, 13:29   #18
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Quote:
Originally Posted by goboatingnow View Post

I fail to see how the male threads of a flanged adaptor provide any more strength then then threads of a through hull , that is properly supported by the correct backing pad thickness and where the tru- hull is then cut to the correct length. MaineSails video clearly demonstrates that the thread fails at the top of the flanged nut, hence it would also fail at the top of the Groco adaptor where the male thread begins, as that is the weakest point.

Unibody flanged seacocks, yes they are different, there is no intervening thread
I don't think so... his videos show that he can't even break it without a fitting and it becomes stronger with the fitting added!
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Old 20-05-2013, 13:34   #19
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Re: Aligning plumbing fitttings

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I don't think so... his videos show that he can't even break it without a fitting and it becomes stronger with the fitting added!
Again I would contend that the failure point on a properly supported thru hull and the Groco flanged adapter is at the start of the threaded section connecting to the associated ball valve. In the tru hull that would be just above the nut, in the adaptor, at the start of the male threads.

The Groco adaptor was designed for basically one purpose to solve the parallel to NPT issue that dogs US tru hulls, it doesnt cause an issue for BSP, because they have full thread engagement, ( we have to seal the threads of course) The groco adaptor is bolted to the GRP to ensure sealing with the underneath tru-hull as was mentioned in another post. it could equally be a large screw-down flange

I see no real strength improvements in the flanged adaptor over a properly installed and backed tru hull that is cut to the proper length.

Unibody seacocks, whether blakes, perco, groco are teh best ( though I hate blakes)

dave
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Old 20-05-2013, 13:50   #20
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Re: Aligning plumbing fitttings

The Groco Flanged Adaptor improves the situation 3 ways: by having a short threaded distance and less lever arm, by providing a thicker shouldered area from the thread to the highest stess point (closest to the hull), and by having a fillet from the shoulder to the flanged part. Compare that with just a thread and nut with no distribution of stress, and no flange to distribute load and I would imagine it's a marked improvement, albeit not as good as a one piece seacock.
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Old 20-05-2013, 13:57   #21
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Re: Aligning plumbing fitttings

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Originally Posted by Cheechako View Post
The Groco Flanged Adaptor improves the situation 3 ways: by having a short threaded distance and less lever arm, by providing a thicker shouldered area from the thread to the highest stess point (closest to the hull), and by having a fillet from the shoulder to the flanged part. Compare that with just a thread and nut with no distribution of stress, and no flange to distribute load and I would imagine it's a marked improvement, albeit not as good as a one piece seacock.
Short threaded distance is equated by the good practice of cutting tru-hulls to length.

" by providing a thicker shouldered area from the thread to the highest stess point (closest to the hull)" yes but all that does is transfer the weakest point to the start of the male threads., Ive already said its likely that both fittings will fail at that point.

The filet etc , yes thats good, but thats not the weakest point in the adaptor.

IN a proper tru-hull fitting there is a proper backing pad to distribute the load and proper support for the bearing faces. the backing pad spreads the loads.
The flange and a nut with a load spreading pad is basically the same idea, equally you could fabricate a nut with a bigger bearing face. This doesnt get away from the point that the tru hull will fail at the unsupported screw threads because the material is at its weakest there, the same is true substantially for the adaptor plate.

Dave
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Old 20-05-2013, 14:20   #22
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Quote:
Originally Posted by goboatingnow View Post

Short threaded distance is equated by the good practice of cutting tru-hulls to length.

" by providing a thicker shouldered area from the thread to the highest stess point (closest to the hull)" yes but all that does is transfer the weakest point to the start of the male threads., Ive already said its likely that both fittings will fail at that point.

The filet etc , yes thats good, but thats not the weakest point in the adaptor.

IN a proper tru-hull fitting there is a proper backing pad to distribute the load and proper support for the bearing faces. the backing pad spreads the loads.
The flange and a nut with a load spreading pad is basically the same idea, equally you could fabricate a nut with a bigger bearing face. This doesnt get away from the point that the tru hull will fail at the unsupported screw threads because the material is at its weakest there, the same is true substantially for the adaptor plate.

Dave
Yes it will fail at that point, but at a multiple of the forces involved. The fitting with nut and valve attached breaks at 400lb, below ABYC recommendation...
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Old 20-05-2013, 14:22   #23
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Re: Aligning plumbing fitttings

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Yes it will fail at that point, but at a multiple of the forces involved. The fitting with nut and valve attached breaks at 400lb, below ABYC recommendation...
Wheres that shown, Mainesails exceed ABYC, but not for Marelon. Ive never seen any data that suggests proper tru-hull and ball valves fail ABYC.

dave
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Old 20-05-2013, 14:32   #24
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Originally Posted by goboatingnow View Post

Wheres that shown, Mainesails exceed ABYC, but not for Marelon. Ive never seen any data that suggests proper tru-hull and ball valves fail ABYC.

dave
Here it is:
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Old 20-05-2013, 16:06   #25
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Re: Aligning plumbing fitttings

Quote:
Originally Posted by goboatingnow View Post
Short threaded distance is equated by the good practice of cutting tru-hulls to length.

" by providing a thicker shouldered area from the thread to the highest stess point (closest to the hull)" yes but all that does is transfer the weakest point to the start of the male threads., Ive already said its likely that both fittings will fail at that point.

The filet etc , yes thats good, but thats not the weakest point in the adaptor.

IN a proper tru-hull fitting there is a proper backing pad to distribute the load and proper support for the bearing faces. the backing pad spreads the loads.
The flange and a nut with a load spreading pad is basically the same idea, equally you could fabricate a nut with a bigger bearing face. This doesnt get away from the point that the tru hull will fail at the unsupported screw threads because the material is at its weakest there, the same is true substantially for the adaptor plate.

Dave
I agree the threads are likley the weak point, but most often the highest stress area will be directly adjacent to the firmest attachment that has no "give" (the hull). By your logic there is no point in filleting/fairing an airplane wing at the fuselage... 'it'll just break further out where is smaller"
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Old 20-05-2013, 17:03   #26
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Re: Aligning plumbing fitttings

Sorry for the drift but a wing root fairing is not structural, it's just for looks and aero. So where the wing breaks off is a different issue.
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Old 20-05-2013, 21:06   #27
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Re: Aligning plumbing fitttings

Back to the problem - when aligning parallel threaded metal fittings, I think a liquid threadlocker with the following characteristics would be useful:

1) Low (non-permanent) strength thread locking
2) Releases when heated above (say) 70 deg C / 160deg F

That would mean it sets firm at room temperature, but goes liquid when moderately heated so you can readily disassemble without burning up the boat.

Don't have a product name for you, but would like thread locking/fastener experts to suggest a product name?
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Old 20-05-2013, 21:37   #28
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Re: Aligning plumbing fitttings

I understand why some boat builders use a ball valve and thru-hull instead of a real seacock. They are building to a price point.

Why do some of you folks use a ball valve instead of a seacock?
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Old 20-05-2013, 22:10   #29
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Re: Aligning plumbing fitttings

Quote:
Originally Posted by goboatingnow View Post
...
The Groco adaptor was designed for basically one purpose to solve the parallel to NPT issue that dogs US tru hulls,
......
Unibody seacocks, whether blakes, perco, groco are teh best ( though I hate blakes)
......
dave
Mainesail said the GROCO flanged adapter passed his ABYC test, but I would suspect not by much, because of the threads, as you pointed out.

In my opinion the other big advantage of these adapters is that you can change the valve if it wears out.

"Unibody" seacocks made by GROCO, Appolo, perko, etc. are just ball valves with an integral flanged base. They are strong and they work great, but not forever. They have plastic seats that will eventually wear out and can not be replaced.

Blakes and Spartan all bronze seacocks are very expensive and require regular maintenance to keep them working, but can last a long time.

The GROCO flanged adapter lets you use a maintenance free valve of your choice and change it out without messing with the skin fitting.
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Old 20-05-2013, 22:33   #30
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Re: Aligning plumbing fitttings

Lots of good info here, however for me I am not considering Groco. I do like the look and design of them, and I thank those for suggesting them, but they are not commonly available in Australia. A Google search did not turn up any retailers with them, and the Groco site does not list any distributors here. The closest is NZ, but their website does not list the marine range.

I assume this is because the NPS/NPT thread is not popular here, as the standard is BSP. Each standard has tapered and non tapered options. While I see comments that they can be fitted together, I understand the threads have a different angle of cut (60 degrees for NPT instead of 55 degrees for BSP), so not an ideal mate.

So rather than mixing thread standards, I prefer to get the BSP fittings commonly available at any local marine shop. In any case, time is now short as the boat comes out of the water this weekend.

Back to my original question ....
Earlier, SWW914 made a comment about prefitting the valves to the skin fittings to ensure good alignment, and this is what I will do. Then, for the skin fittings where I am only replacing valves, I will deal with them using tape and sealant.

Quote:
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Did you check out MainSail's pages about this?
Yes, thanks for the recommendation. Mainsail has some useful info even if I don’t follow his Groco advice.
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