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Old 19-10-2018, 06:13   #1
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Bronze Through Hulls and Seacocks in Steel Boat

I know that many of you are going to talk about the ease of welding a threaded pipe to the boat and that in many places in the world this is the preferred method. But please, I would just like to hear opinions about this particular set up that we are planning and what your thoughts are about it. I believe everything is isolated correctly and that there are no issues with this but I'd love to hear what everyone has to say.


The backing plate would be installed to the seacock before install, with polysulfide using the bronze fasteners. The hole in the hull will be drilled about 1/8" larger than the OD of the through-hull. I hope my drawing meets everyone's artistic standards.


OK...Give it to me straight Doc.
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Old 19-10-2018, 06:35   #2
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Re: Bronze Through Hulls and Seacocks in Steel Boat

Ummmm. Marelon.

The bronze is an awful idea, there is still a current path seeing as you’re immersed in electrolyte.
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Old 19-10-2018, 07:00   #3
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Re: Bronze Through Hulls and Seacocks in Steel Boat

Thank you for the reply but I am specifically interested in bronze. We purchased this boat a year ago and this was done on our boat for the last 15 years with no corrosion problems. I have also heard from others who have not had any problems as long as things are correctly isolated (if only I had quizzed them further when I had the chance!). Unfortunately, it was not installed strong enough; it had no backing plate. We are replacing all our seacocks and removing half of them during this refit.

Marelon was considered but it is not going to work for us so we are interested only in people who have specific success in using bronze fittings with a metal hull.

Thanks.
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Old 19-10-2018, 07:19   #4
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Re: Bronze Through Hulls and Seacocks in Steel Boat

Out of interest, why did you decide against Marelon?
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Old 19-10-2018, 07:46   #5
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Re: Bronze Through Hulls and Seacocks in Steel Boat

Quote:
Originally Posted by strongmonty View Post
I know that many of you are going to talk about the ease of welding a threaded pipe to the boat and that in many places in the world this is the preferred method. But please, I would just like to hear opinions about this particular set up that we are planning and what your thoughts are about it. I believe everything is isolated correctly and that there are no issues with this but I'd love to hear what everyone has to say.


The backing plate would be installed to the seacock before install, with polysulfide using the bronze fasteners. The hole in the hull will be drilled about 1/8" larger than the OD of the through-hull. I hope my drawing meets everyone's artistic standards.


OK...Give it to me straight Doc.
You can use G10 for the backing plate. A really good how to is here: https://marinehowto.com/seacock-backing-plates/
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Old 19-10-2018, 08:37   #6
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Re: Bronze Through Hulls and Seacocks in Steel Boat

Thank you kmacdonald for the link. I had found that site and had written it off as it was for GRP boats but looking at it again, I see they used the backing plate idea that was basically the same as ours (but with an even better idea for the bolts!).
CarlF, we aren't going to use marelon (although we really wanted to!) Because we are setting the boat up for high latitude sailing and plan to be hanging around Tierra del Fuego a bit. Lots of rocks around there and many places still have very bad charts. Were we to hit a rock there, we will feel much more comfortable hitting a bronze mushroom as opposed to a marelon. Many people claim them to be of equal strength, but if you look at their stats, there is a strength difference of almost 50% (I think I'm remembering that number correctly). In most people's case that is probably not an issue to be concerned with but for us that difference could make the difference.
Anyone have any thoughts on our isolation?
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Old 19-10-2018, 08:45   #7
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Re: Bronze Through Hulls and Seacocks in Steel Boat

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Originally Posted by kmacdonald View Post
You can use G10 for the backing plate. A really good how to is here: https://marinehowto.com/seacock-backing-plates/
After Maine Sail wrote this article, Groco took the (excellent) idea and put it into production. They're designed obviously to fit Groco's flanged seacocks and flanged adapters, but I believe I saw somewhere that they can also be used with Apollo seacocks (same bolt pattern apparently). https://www.groco.net/products/valve...backing-blocks
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Old 19-10-2018, 09:08   #8
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Re: Bronze Through Hulls and Seacocks in Steel Boat

Bronze sea valves on steel hulls is the norm for commercial / milspec vessels.
(Anyone that says its a bad idea has no idea what they are talking about...but that's often the norm on these forums.)
Typically steel hulls have a flanged steel spool piece welded to the hull. The valve is then fastened to the spool piece with appropriate gasket. Often waster pieces are installed as reassurance against corrosion.
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Old 19-10-2018, 09:12   #9
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Re: Bronze Through Hulls and Seacocks in Steel Boat

Have you considered a sea chest instead of individual through hills? Gives you great safety, if you have the space for it.
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Old 19-10-2018, 09:19   #10
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Re: Bronze Through Hulls and Seacocks in Steel Boat

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Originally Posted by Jetx View Post
After Maine Sail wrote this article, Groco took the (excellent) idea and put it into production. They're designed obviously to fit Groco's flanged seacocks and flanged adapters, but I believe I saw somewhere that they can also be used with Apollo seacocks (same bolt pattern apparently). https://www.groco.net/products/valve...backing-blocks
JetX beat me to it. He is absolutely right.
I really like Groco products and wouldn’t hesitate to use either their imported seacocks or their American made seacocks. Apollo Seacocks are equally as good. I believe they were the first to come out with a ball valve flanged seacock. I had Apollo seacocks on my boat for 28 years with no maintenance and no failures.

The Groco backing blocks took Maine Sail’s idea and went him one better. They have metal threads for the bolts to screw into. I highly recommend them.
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Old 19-10-2018, 10:07   #11
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Re: Bronze Through Hulls and Seacocks in Steel Boat

We have a sea chest on MOJO for all intake water. Steel welded threaded pipes on the side of the sea chest with bronze ball valves. The sea chest opening (maybe 10" x 10") has a bronze grill over it. 18 yrs w/out any corrosion. Head thru hulls are welded threaded SS pipe w/bronze valves. Curious why you're not going with welded thru hulls - nothing to break in a grounding since no external protrusions from the hull.
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Old 19-10-2018, 18:15   #12
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Re: Bronze Through Hulls and Seacocks in Steel Boat

Gilbert Klingel's steel boat building book has a good diagram of this setup if you can get a copy of it.
I think you would do better just machining a stainless stub and welding it into the hull with the appropriate electrode. This is what we do and seems pretty bullet proof.


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Old 19-10-2018, 18:25   #13
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Re: Bronze Through Hulls and Seacocks in Steel Boat

I am not going to try to convince you for or against bronze. Certainly if done right, there is nothing wrong with it. BUT... The design you have drawn has a flaw that to me is very serious.

Once mounted... how can you remove the valve?????

I know, I know... you do not expect to ever have to. But you will.
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Old 19-10-2018, 22:54   #14
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Re: Bronze Through Hulls and Seacocks in Steel Boat

The Groco full-flow flanged seacock can be serviced w/their kit, consisting of a new ball & teflon seals, w/o removal from the hull.

On the subject of protecting the external face of the thru-hull fitting, I think I recall seeing steel hull commercial fishing boats with a donut ring made from solid round stock welded onto the exterior of the hull around each thru-hull.
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Old 20-10-2018, 22:41   #15
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Re: Bronze Through Hulls and Seacocks in Steel Boat

I surveyed a steel yacht last Wednesday that had been built in 1990. All the through hulls and seacocks were bronze and there was zero signs of any corrosion around the fittings on the hull. There was no backing plates, just the bronze nut fitting tightly against the inside of the hull.
The boat had been home built and the current owner had no idea why the skin fittings had been done like that.
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