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Old 23-12-2011, 23:56   #16
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Re: PVC Seacocks..?

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Originally Posted by osirissail View Post
Wow, there are some sharp-eyed folks on this forum! I missed the copper pipes and then the really unacceptable electrical wiring in the first photo. But I get the impression the boat is still being constructed as their are wooden spacer blocks in the second photo.

Although things, especially plastics, are always improving, I am still not happy with the use of those PVC seacocks. In my experience PVC valves tend to be quite "brittle." Especially when they are threaded onto a metal pipe with NPT threads. The PVC plastic is under serious stress and frequently fractures.

From the Marelon spec sheets their "marine seavalve is made of MARELON®, a glass reinforced nylon composite." To me this means a greater ability to absorb attachment stresses than brittle PVC.

There was a rumor about the E.U. not allowing Marelon on aluminum boats, but I cannot find any authoritative links on the subject so it seems to be just a rumor. But anyway, why not use stainless steel ball valves which are easily available - I see them on boat store shelves in all the French Islands and elsewhere.
Don't ferget the stainless shackles in the aluminium rail on the bottom. There's a LOT of corrosion potential in that picture
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Old 23-12-2011, 23:57   #17
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Re: PVC Seacocks..?

BTW, I always take manufacturers data with a grain of salt. Of course the Marelon valves are better then everyone else, at least on Marelon Co paper. The tensile rating is a material is based on a square inch of material under tension and has only a little correlation to valve body design. Data such as pressure rating, wall thickness, handle / shaft design are more important. Every manufactures materials work great in the lab.

In engineering, valve design is very much like anchor design and we all know what thats like. The weakness of a ball valve is not so much valve body strength, but the shaft/ ball connection. Ball valve failure is almost always at the shaft, on land or sea.
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Old 24-12-2011, 00:04   #18
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Re: PVC Seacocks..?

Also Aluminum is an anode to stainless too. So on aluminum hulls you want to only use aluminum valves (rare as hens teeth) or plastic valves. anything else will cause the aluminum to corrode around the valve, so not good...
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Old 24-12-2011, 01:48   #19
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Re: PVC Seacocks..?

Wow, thank you everyone so much for your feedback. I've learned so much.

I will check the threads on the welded pipes/thruhulls. Am I understanding this threading issue correctly?

A) If the pipes have tapered threads, then I cannot switch to Marelon seacocks, since they are made for straight threads (unless I want to weld new pipes to the hull with straight threads, or cut the threads deeper on the existing pipes so that they are straight).

B) If the pipes have straight threads, then I must switch to Marelon seacocks, since most PVC valves are made for tapered threads and are thus barely hanging on by a few threads.

Is this correct?

I want to do whatever is reasonably best, so the cost of replacing the valves with Marelon is not an issue. But after reading the recent discussion here (and a few other boards) it seems like folks are not ecstatic with them: the handles on 'normal' sizes (< 1.5") break off easily and then water leaks through the hole. So I thought-- maybe whoever decided to use PVC valves on this boat was thoughtful and had a good reason that was not just "save $70." Maybe they had marelon seacocks and threw them all out in a fit of rage. I'm sometimes skeptical of 'marine grade' products, and feel that certifications are often more of a marketing choice than a measure of the quality of the product.

For the other questions:
The copper tubing is for hydraulic steering. The runs are relatively short and it doesn't touch the hull anywhere that I've seen, but thank you for the heads up-- I will look more thoroughly (with a mirror) to make sure it doesn't touch anywhere hidden. My last boat had the bicycle chain & quadrant style steering, so the hydraulics is also new to me.

Some of the electrical wiring is a mess, and yes, the surveyor was not happy at all with it. I have a few questions about that (this is my first aluminum boat)... But my overall plan is to vastly simplify the boat, to eliminate a lot of devices and the wiring and complication they bring, and then bring whats left up to a higher standard.
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Old 24-12-2011, 05:03   #20
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Re: PVC Seacocks..?

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Originally Posted by msponer View Post
Wow, thank you everyone so much for your feedback. I've learned so much.

I will check the threads on the welded pipes/thruhulls. Am I understanding this threading issue correctly?

A) If the pipes have tapered threads, then I cannot switch to Marelon seacocks, since they are made for straight threads (unless I want to weld new pipes to the hull with straight threads, or cut the threads deeper on the existing pipes so that they are straight).

B) If the pipes have straight threads, then I must switch to Marelon seacocks, since most PVC valves are made for tapered threads and are thus barely hanging on by a few threads.

Is this correct?

I want to do whatever is reasonably best, so the cost of replacing the valves with Marelon is not an issue. But after reading the recent discussion here (and a few other boards) it seems like folks are not ecstatic with them: the handles on 'normal' sizes (< 1.5") break off easily and then water leaks through the hole. So I thought-- maybe whoever decided to use PVC valves on this boat was thoughtful and had a good reason that was not just "save $70." Maybe they had marelon seacocks and threw them all out in a fit of rage. I'm sometimes skeptical of 'marine grade' products, and feel that certifications are often more of a marketing choice than a measure of the quality of the product.

For the other questions:
The copper tubing is for hydraulic steering. The runs are relatively short and it doesn't touch the hull anywhere that I've seen, but thank you for the heads up-- I will look more thoroughly (with a mirror) to make sure it doesn't touch anywhere hidden. My last boat had the bicycle chain & quadrant style steering, so the hydraulics is also new to me.

Some of the electrical wiring is a mess, and yes, the surveyor was not happy at all with it. I have a few questions about that (this is my first aluminum boat)... But my overall plan is to vastly simplify the boat, to eliminate a lot of devices and the wiring and complication they bring, and then bring whats left up to a higher standard.
Good on you. As long as you obviously recognize the issues and address them I'll sleep better at night.
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Old 24-12-2011, 05:28   #21
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Re: PVC Seacocks..?

Gotta disagree with the crowd favoring the ball valves pictured. Come on guys this isn't your sprinkler system at home. The issue is not if the ball valve itself will work, any Home Depot valve you can fit will work. But just because something works don't make it right. You could knob and tube this boat and it would work. The issue is the installation shown. There's a very good reason quality Marine grade valves are designed the way they are. I don't suspect them at all! The installation of the valve shown is horrible. That valve IS NOT secured in any way acceptable at all. It will take little side pressure before it fails right at the very small and very thin threaded plastic connection. If msponer insists on keeping these valves at the least a better solution is to remove them from the aluminium threads, add a proper marine grade nylon thread to hose barbed fitting to the threaded nipple, add a short section of hose and route it to the valve body that has been properly mounted and secured to a ridged support. This way the valve has far less threat of side attack at the threaded coupling.
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Old 24-12-2011, 09:47   #22
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Re: PVC Seacocks..?

HUM....The problem is metal marine seacocks / valves are not compatible with aluminum hulls. Aluminum is an anode to just about anything else. That requires that all copper, bronze and steels, be isolated from the aluminum.

I'm pretty sure that nylon fittings are not listed or rated as marine grade. Nor would I put a nylon fitting between the sea and a valve. Its just too soft of a material.

I do agree that providing a support (wood maybe) off the hull to any valve with a long standpipe is a really good idea. Besides damage to the valve it could bend the pipe or crack a weld due to the longer lever arm. That would be the best of all worlds

To the OP yes on your A and B notes, Got it exactly.
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Old 24-12-2011, 10:02   #23
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Re: PVC Seacocks..?

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Originally Posted by msponer View Post
. . . A) If the pipes have tapered threads, then I cannot switch to Marelon seacocks, since they are made for straight threads (unless I want to weld new pipes to the hull with straight threads, or cut the threads deeper on the existing pipes so that they are straight).

B) If the pipes have straight threads, then I must switch to Marelon seacocks, since most PVC valves are made for tapered threads and are thus barely hanging on by a few threads.

Is this correct?. . .
Actually Marelon comes in 2 types - actual "Seacocks" which are normally flanged and made to be attached using "Through-hull" fittings and have threading to match standard "Through-hull" fittings.

- - The other type are "Ball Valves" which I pictured. From the Marelon website about their "Ball Valves:"
"All valves sold throughout the U.S.A. have N.P.T. type threads. If specified, B.S.P. are available on valves sold outside of America."

- - By the way, the "breaking off of valve handles" is not restricted to only Marelon, I have had plenty of PVC ball valves that could not be turned without breaking off the handle stem - even with valves in the store shelves. And even bronze seacocks can have "frozen" valves and forcing them will break the handle or stem.

- - Any valve, be it metal or plastic or composite, has to be operated and lubricated periodically to keep it functional.

- - The Marelon seacocks and ball valves - most probably just like PVC versions come in parts that "compress" the ball valve to prevent leaking. Those "parts" of the valve can be moved (rotated) to lessen the pressure on the actual "ball" part of the valve so that a "stuck" valve can resume functioning.

- - Specifically with Marelon it only takes a 1/8th rotation of the base to body to free up a stuck handle. If you exercise and lubricate the valve (all versions) you will not have "stuck" handles. Unfortunately, these valves are normally "out of sight" and so end up "out of mind" and lubrication and exercising gets forgotten.

- - Be the valves, Marelon, PVC (Hayward or Home Depot or whatever) or anything else they will most probably do the job. The question becomes one of what does your insurance company require (which can vary with individual surveyor's opinions) and secondly, what is the best type considering your hull material.

- - Obviously as stated by others, Aluminum is a bit touchy about what other metal is attached to it. Non-metallic is an easy fix but then you get into relative strength of materials as related to operating in a marine vessel environment.

- - So you gather all the opinions and information you can and then you make your decision. After all, it is your butt riding in the boat, not any of ours.
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Old 24-12-2011, 10:31   #24
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Re: PVC Seacocks..?

Wow a civil discussion. How nice. I have an idea for the copper line. Have you thought of buying some pex pipe and splitting it lengthwise and putting it over the copper pipe so that the copper and the aluminum cannot touch. A second idea which is an out of the box in the box idea would be to create a box that would attach to the ribs around the thru hulls. make the box large enough so that it is easy to operate the valves. The box would make it difficult to step on the valves and break them. Seems like the thread type is the most important item though.
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Old 24-12-2011, 10:38   #25
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Re: PVC Seacocks..?

I have had schedule 80 PVC valves and fittings fail in service in industrial applications. Some of them simply broke in half in minor vibration situations. Marelon would be nice but I think they are straight threads not tapered pipe thread and the handles break off. Marelon is tough stuff though. I had to chisel a Marelon thru hull out of my catamaran, and it came out one small piece at a time. There is no way you can break it! In your situation, replacing a Mrelon valve as opposed to a seacock, wouldnt be that tough when you break the handle off...... of course Murphy loves Marelon... and the handle will break off only in an emergency...!!! Maybe just replace the PVC ecvery 2-3 years? High end alum boat builders use stainless steel valves dont they?
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Old 24-12-2011, 10:39   #26
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Re: PVC Seacocks..?

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BTW, I always take manufacturers data with a grain of salt. Of course the Marelon valves are better then everyone else, at least on Marelon Co paper. The tensile rating is a material is based on a square inch of material under tension and has only a little correlation to valve body design. Data such as pressure rating, wall thickness, handle / shaft design are more important. Every manufactures materials work great in the lab.

In engineering, valve design is very much like anchor design and we all know what thats like. The weakness of a ball valve is not so much valve body strength, but the shaft/ ball connection. Ball valve failure is almost always at the shaft, on land or sea.
I don't know of a single PVC valve that meets or passes the minimum ABYC/UL/ANSI tests or requirements to meet the definition of a seacock? Perhaps someone can point me to one?

Considering I am replacing some cracked sched 80 PVC fittings this week, that were installed below water, and mated to Marelon valves, that are perfectly fine and did not fail, and I have seen PVC crack before, I simply do not and will not use it if it does not have a Marine UL label on it. Marelon meets the standard as to bronze & stainless fittings that carry the UL Marine Label. Of course on an aluminum boat you want to be mindful of corrosion so that most often rules out metallic fittings. Dupont Zytel, which is what Marelon is, is TOUGH stuff and far stronger than PVC in this application. At a minimum the Marine UL label tells me the product has been tested to a minimum standard for the marine environment, which includes corrosion tests for metallic fittings, and can withstand the 500 pound static load test..

"27.5.4 Seacocks shall be designed and constructed to meet ANSI/UL 1121, Marine Through-Hull Fittings and Sea-Valves.

27.6.1.3 Threads used in seacock installations shall be compatible (eg. NPT to NPT, NPS to NPS)."


I suspect the OP will be fine so long as he is mindful of them but it would not be my choice.....

This was a cracked PVC elbow from a job last summer (between the bucket and cooler). The Marelon valve & thru-hull it was connected to it were perfectly fine. The elbow was split and weeping at the Marelon thru-hull to PVC female threads as it was a thread mismatch and the sched 40 PVC lost the battle. Luckily the elbow was above static when sitting still but it leaked when sailing or under power.. Just some loose stuff in the locker, & a thread mismatch caused it to crack & leak.. I've seen plenty of Marelon valves threaded to NPT bronze, a thread mis-match, and never seen one split...
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Old 24-12-2011, 11:02   #27
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Re: PVC Seacocks..?

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. . . I have an idea for the copper line. Have you thought of buying some pex pipe and splitting it lengthwise and putting it over the copper pipe so that the copper and the aluminum cannot touch. . . .
Diverging off the primary discussion - there are non-metallic hydraulic lines made from some form of really high pressure "plastic" that can be used instead of copper tubing. They are shown in the vendor catalogs along with the other hydraulic steering system parts. See: Hynautic 500psi Nylon Tubing
- - In a valiant effort to remove all "metallic" or as much "metallic" stuff from my boat, I purchased and installed these new hydraulic tubing. Installing the tubing was a breeze as it is flexible and bends around corners quite well. But it was a nightmare of trying to get fitting onto the ends of the tubing. After much discussion with the technical folks at the manufacturer I even made their special installation tool since you could not buy one. Still the system leaked. So I ripped out the new and put back the old.
- - Now this was 15 years ago and I am told the latest versions do not have the problems I encountered. So it might be worth a look to see if you can eliminate those copper tubes.
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Old 24-12-2011, 11:21   #28
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Re: PVC Seacocks..?

Also diverging- Congratulations Msponer! We talked a lot about this boat before you bought, I'm pleased for you. Hadn't heard you got her for sure. Have fun!
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Old 24-12-2011, 11:21   #29
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Re: PVC Seacocks..?

One has to be very careful using tensile ratings and pressure ratings. Boats see nothing near the pressure rating of most fittings, but toughness and resistance to cracking are very important. Window glass has a very high tensile rating, but the yield strength is very close to the tensile strength.... therefore if it bends at all.... it breaks! On paper it is very strong though.
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Old 24-12-2011, 11:37   #30
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Poor installation is not an argument against a material type. Mismatched threads and schedule 40 do not relate to this thread. Any material installed incorrectly can fail.

In that picture it looks like the sched 40 PVC was female threaded and the valve was probably overtightened into it, most likely in an attempt to turn the valve to a desirable, usable position.

Even an engine block can be cracked by over tightening tapered plugs.

White schedule 40 valves with the red handles like you see at home depot can and usually do get stuck and break. They are not comparable to The Hayward valves we are talking about here, which are serviceable and rebuildable.


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