Flanged seacocks vs Inline Valve with Thruhull and backing block

[blueazimuth]

My mentor taught me that seacocks should be installed with a wooden backing block, shaped to the hull and that it should be hardwood, and never, ever plywood.

[Terra Nova]

Originally Posted by blueazimuth

My mentor taught me that seacocks should be installed with a wooden backing block, shaped to the hull and that it should be hardwood, and never, ever plywood.

Solid wood can easily crack along the short grain. Quality marine ply is better (epoxy saturated). Solid glass even better.

[bcboomer]

I have had Schedule 80 grey pvc fittings 2"- 3" catastrophically break in industrial use . Those things are super thick.
Hopefully Tru Design are getting somewhere with using the material, but I'm not holding my breath.

They are as far from PVC as your hull is. They are a composite, like your hull, and just as durable. Because they are stable, they are still as easy to turn as the day they were installed.

I'm not sure what your " The thru hulls become part of your hull" means though?

The composite thru hull is epoxied to the composite hull. Can't separate, can't leak, can't corrode, no stray current issues.

[ZULU40]

Originally Posted by bcboomer

I have had Schedule 80 grey pvc fittings 2"- 3" catastrophically break in industrial use . Those things are super thick.
Hopefully Tru Design are getting somewhere with using the material, but I'm not holding my breath.

They are as far from PVC as your hull is. They are a composite, like your hull, and just as durable. Because they are stable, they are still as easy to turn as the day they were installed.

I'm not sure what your " The thru hulls become part of your hull" means though?

The composite thru hull is epoxied to the composite hull. Can't separate, can't leak, can't corrode, no stray current issues.

Its a storm
a battery or similar or heavier weight cuts loose
on impact the leverage enables it to break

have no doubt epoxy joints are strong
usually stronger than that of the material being joined
that doesnt make plastic valves invulnerable to damage or breakage
the only way to do that is to eliminate thru-hulls, no matter what they are
being a lower profile would help, but theyre not

[Terra Nova]

In the event of a fire, which would you rather have, metal or plastic thru-hulls and sea cocks?

[stormalong]

Originally Posted by Terra Nova

In the event of a fire, which would you rather have, metal or plastic thru-hulls and sea cocks?

Have you ever seen fiberglass burn? In the event of a fire the sea cock melting would be the least of my worries.

[bcboomer]

If the battery or whatever breaks loose the Trudesign meet the ABYC specs for a 500 lb force so it's just as likely to survive. Who knows how strong that bronze is after 10 years of various marinas with various amounts of stray current. There really isn't any way to know. My boat doesn't have any thru hull valves sharing space with large or heavy things anyway. If it did, even with bronze on a flange, I'd be looking at some kind of barrier.

When we bought our boat the surveyor condemned the bronze thru hulls based on looking at the surface condition. The galley drain was seized and I didn't dare put too much pressure for fear of breaking it off. I was nervous about them but when I took them out they were actually pretty solid.
Now I don't give them a second thought. They close and open easily and I don't worry about then rotting away. There are enough things that need attention on a boat so it's nice to have 1 less.

As far as fire is concerned, I don't think it will matter a tinker's damn whether the valve is metal if the hull is plastic.

Come to think of it, the Trudesign people did demonstrate to the local distributor how they stand up to a flame. The bulkheads, hull, deck etc will be gone before the valve leaks.

[coastalexplorer]

Does anyone know IF there are any other manufacturers of Marlon or glass filled plastic through hulls other than Tru-design of New Zealand, and Forespar Corporation of California? ...Who seem to love that slogan get out of the Bronze age!

My Engine space floor is 2-1/4" thick. Groco Make a 3/4" extra long bronze through hull 5.3" long. This currently seems to be My only option as Forespar have no intention to manufacture a comparable fitting and My second hand information is that Tru-design do not intend to make any until the Fall.

That seems too long to wait. It seems to me that many traditional planked vessels would have the same requirement as I have?

[cal40john]

So they show their idea for best practice for inline valves, but the OP's link states that they don't recommend it.

I added the bold -

IN-LINE VALVE INSTALLATION
GROCO does not recommend the use of in-line valves as seacocks for these reasons:

An in-line valve has no means of attachment to the vessel hull or backing block, so the valve can turn or loosen from the thru-hull fitting with vibration or with normal use.
If the connected thru-hull fitting becomes damaged or broken, as might occur if the vessel struck a submerged or floating object, or if the fitting was inadvertently damaged or broken inside the hull, there would be no way to shut off the flow of water into the vessel.
In-line valves have NPT threads, which are not compatible with NPS threaded thru-hull fittings (unless the thru-hull fitting is machined with "Combination Thread". Installing an in-line valve onto a thru-hull fitting will create a mismatch of threads resulting in minimal thread engagement between valve and fitting, and an unsafe installation. Property damage, personal injury, or both could occur. If you choose to utilize an in-line valve as a seacock, the thru-hull fitting used must have "Combination Thread".

[KP44]

I found one (unused) bronze seacock with a black iron fitting that had welded itself to the bronze. I could break the soft, rotten iron with my hand. Made me look at all 13 seacocks and throughhulls.
Some I have completely eliminated. A couple were frozen and the bronze handle broke off from the effort to open or close the valve. Years of electrolysis?
Every replacement has been Marlon throughhull and Marlon seacock. No worries about electrolysis. No thoughts about the occasional blown-out throughhull from a lightning strike.
The first replaced throughhull was over 10 years ago and the seacock works easily and perfectly. I have heard a lot of bad about plastic throughhulls used above waterline for bilge or cockpit drains. But have never heard of broken or deformed Marlon.

[Tessellate]

Originally Posted by cal40john

GROCO does not recommend the use of in-line valves as seacocks for these reasons:

True, I saw that but it's just a whole bunch of speculation without any data backing it up. Pretty frustrating that not only does the boating community speculate about boat sinking causes without citations, but the manufacturers do too.

Originally Posted by cal40john

(Groco quote):
1) An in-line valve has no means of attachment to the vessel hull or backing block, so the valve can turn or loosen from the thru-hull fitting with vibration or with normal use.

I don't see how this is an issue. The inline valve is not going to just turn itself - it has hose(s) attached which prevent full rotation. So it's never going to unscrew itself, unless the hose actually isn't secured to it, in which case you have a potential leak/flood anyway, and how is vibration loosening the valve if nothing's attached to it?

Maybe they're making the point that you could have a 1/16 turn or so which could cause a very tiny leak at the pipe threads. This just doesn't seem likely to me (the valve is very tightly screwed on) or very concerning (a tiny thread leak won't sink a boat).

Originally Posted by cal40john

(Groco quote):
2) If the connected thru-hull fitting becomes damaged or broken, as might occur if the vessel struck a submerged or floating object, or if the fitting was inadvertently damaged or broken inside the hull, there would be no way to shut off the flow of water into the vessel.

So striking a submerged object is going to destroy a bronze thruhull, but not the fiberglass hull it's bedded in? Sorry I just don't buy this. Do they have any data on it?

I see their point that if you break the fitting inside the boat it's a bit harder to stop the flow of water, but this is irrelevant unless there's actually an issue of many boats sinking due to inline valves breaking off inside the hull. Otherwise it's just speculation about something that isn't a problem.

This really seems like a concern about electrolysis, which is legitimate but is an argument for using Marelon, because both inline bronze and flanged bronze are susceptible to electrolysis.

Also saying there's no way to shut off the flow is ignoring the dozens of ways we have for dealing with an emergency hull leak - StayAfloat putty, wooden dowels, underwater epoxy, rubber bung, etc. A flanged seacock isn't a guarantee of never having that kind of issue.

Originally Posted by cal40john

(Groco quote):
3) In-line valves have NPT threads, which are not compatible with NPS threaded thru-hull fittings (unless the thru-hull fitting is machined with "Combination Thread". Installing an in-line valve onto a thru-hull fitting will create a mismatch of threads resulting in minimal thread engagement between valve and fitting, and an unsafe installation. Property damage, personal injury, or both could occur. If you choose to utilize an in-line valve as a seacock, the thru-hull fitting used must have "Combination Thread".

This is a valid point, although they include the counterpoint in their own point, so they're really just saying here that some people install inline valves incorrectly, and you shouldn't do that. Although it would also be great to get real world data - how many boats sink due to thread mismatch?

[Terra Nova]

Unsubscribed.

[Mistress Sirena]

after having encountered a few frozen ball valve"seacocks "I will choose the cone style bronze sea cocks when I can find them.

[clockwork orange]

Originally Posted by Terra Nova

Solid wood can easily crack along the short grain. Quality marine ply is better (epoxy saturated). Solid glass even better.

correct on all accounts

[bcboomer]

Originally Posted by Mistress Sirena

after having encountered a few frozen ball valve"seacocks "I will choose the cone style bronze sea cocks when I can find them.

Hmm, tapered bronze that I understand require regular maintenance, lapping in, lubricating, exercising, protecting from stray current, etc, etc. Why not use Trudesign composite? No maintenance, lubrication, exercising or corrosion.
If you are looking for high maintenance why not go back to a wood hull?