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Old 24-10-2012, 14:20   #1
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Thru Hull Materials

We are aiming to haul shortly and we believe the thruhulls are original (1967) so replacing seems like a good idea even though we have very little corrosion and no visable 'pinking' on them.

I have been looking at thru hulls and would like to hear the rationale for bronze over stainless over the plastic materials.

I know there is a price differential of course, and I suspect I am going to hear that "Bronze is the ONLY way to go!" and I am OK with that as well.

On the flip side for me I look at the plastic and think, "gee, no zincs, no corrosion, no electrolysis...", what's not to like about that?

Bring it on ; -)
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Old 24-10-2012, 14:34   #2
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Re: Thru Hull Materials

Check 'Main Sail's' sites, he has been running tests of strength to failure, all his work is well worth reading/watching. Bruce.
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Old 24-10-2012, 14:34   #3
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Re: Thru Hull Materials

Love the Tru Design Thru Hulls & Ball Valves

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Old 24-10-2012, 14:34   #4
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Re: Thru Hull Materials

All my below-water thruhulls are original bronze, with Groco valves. I don't bond anything. They are in beautiful condition. I have other metals underwater: stainless steel shaft, bronze folding prop, stainless rudder hardware. The rudder hardware is now 5 years old (no problems, I simply wanted to build a nicer one), but all the rest is about 35 years old. I use plastic above the water line.
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Old 24-10-2012, 14:35   #5
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Re: Thru Hull Materials

You are right about the plastic Sara, you just have to exercise the plastic valves much more frequently than you would silicon bronze so they don't seize up on you.
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Old 24-10-2012, 14:51   #6
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Re: Thru Hull Materials

The problem with the plastic ones is that to the best of my knowledge not a single one has been certified to ABYC H-27 standards. Which basically tests if they will snap if you accidentally step or pull on one. This isn't a rigorous test for most metal ones, but the plastic just snaps. Worse, the plastic snaps right where the pipe exits the fiberglass, which means there is no possibility of repair until the boat is hauled and a new one can be fitted.

The only way to prevent sinking is to have a plug large enough to plug not only the stand pipe of the thru-hull, but also the hole drilled into the fiberglass.
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Old 24-10-2012, 14:58   #7
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Re: Thru Hull Materials

Quote:
Originally Posted by sarafina View Post
We are aiming to haul shortly and we believe the thruhulls are original (1967) so replacing seems like a good idea even though we have very little corrosion and no visable 'pinking' on them.
They might still be outlive most thruhulls bought today..
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Old 24-10-2012, 15:01   #8
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Re: Thru Hull Materials

Quote:
Originally Posted by Stumble View Post
The problem with the plastic ones is that to the best of my knowledge not a single one has been certified to ABYC H-27 standards. Which basically tests if they will snap if you accidentally step or pull on one. This isn't a rigorous test for most metal ones, but the plastic just snaps. Worse, the plastic snaps right where the pipe exits the fiberglass, which means there is no possibility of repair until the boat is hauled and a new one can be fitted.
I believe Incorrect.

Marelon is: A.B.Y.C. H-27

Also the marelon thru hulls are EXTREMELY tough. I have wacked on them sideways with a sledge hammer and could not break them.

As to the original question . . . I think stainless would be the clear last choice of the three (because of potential pitting problems). I personally prefer the operation of bronze valves to the marelon ones, but prefer the absolute corrosion resistance of marelon. I have an aluminum boat so there was an obvious choice for me (had to be marelon), but with a glass boat it would be a toss up.
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Old 24-10-2012, 15:21   #9
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Re: Thru Hull Materials

Do look at Mainsail's site but a summary of his findings:

Forespar OEM ("Series 93") valves with correct Forespar thru hull do pass H-27 (500 lb side load) as do proper bronze seacocks.

The other kind of Forespar valve does not pass as well as bronze valves simply screwed to a thru-hull - a common method used today on production boats.

People continue to be confused between the two kinds of Forespar valves (I don't know why Forespar doesn't clear it up) They are two completely different designs. I have never experienced or even heard of a Forespar 93 Series valve handle breaking or the valve swelling such that it doesn't operate smoothly - both common problems with the other kind of Forespar valve.

I exercise mine once a year, never grease them, and they're "like new".

Here's what the Forespar Series 93 valve looks like:

Mushroom Thru-Hull Ball Valve


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Old 24-10-2012, 15:24   #10
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Re: Thru Hull Materials

Quote:
Originally Posted by sarafina View Post
We are aiming to haul shortly and we believe the thruhulls are original (1967) so replacing seems like a good idea even though we have very little corrosion and no visable 'pinking' on them.

I have been looking at thru hulls and would like to hear the rationale for bronze over stainless over the plastic materials.

I know there is a price differential of course, and I suspect I am going to hear that "Bronze is the ONLY way to go!" and I am OK with that as well.

On the flip side for me I look at the plastic and think, "gee, no zincs, no corrosion, no electrolysis...", what's not to like about that?

Bring it on ; -)
Are you talking replacing just the thru hulls or the seacocks? What type are yours now? If tapered bronze, simply clean, lube and inspect. Age doesnt matter. You should expect no significant corrosion in bronze either.
*I've had Marelon, Basically tough stuff but the inherent weak link causes failures. Only seacock I've ever had that failed in service.
*I've used heavy duty PVC in industrial applications, had several failures in service also.
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Old 24-10-2012, 15:29   #11
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Re: Thru Hull Materials

i used marelon on my ericson and on my 26 islander i used to have--good stuff. might want to look into it.
if i can find marelon when it is time to change these, i may use it with many of mine on this formosa...
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Old 24-10-2012, 15:37   #12
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Re: Thru Hull Materials

1962 Monk 36' has all original metal (bronze) below the waterline incuding shaft. The prop is replaced at 5 or 6 year intervals and the only zinks on the boat are in the exhaust manifold and the heat exchanger. Jesse
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Old 24-10-2012, 15:45   #13
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Re: Thru Hull Materials

It isn't the series 93 that you want but the proper flange mounting sea cock.

Boat Marine Plumbing Flange Mounting Seacock Thru Hull

However if your bronze sea cocks are in good shape, keep them. You may not be able to get the same quality any more.
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Old 24-10-2012, 16:07   #14
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Re: Thru Hull Materials

Bronze is a bit better in seawater service, but don't settle for something that just says bronze. Find out the ASME number like B-62. No one seems to want to state what the actual material is. Bronze can be quite a range of materials.
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Old 24-10-2012, 16:28   #15
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Re: Thru Hull Materials

I wonder how many pages of comments it will take for the last person to recognize the answer is a matter of opinion.
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