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Old 06-12-2011, 11:27   #1
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Seacock Question

Hello,

I'm replacing a sea cock and deciding on a few things:

Is Starboard acceptable as a backing plate?

And do Bronze sea cocks with stainless ball valves increase the need to be bonded because of the two metals in the valve, where as a fully bronze old style with the barrel cone valve being bronze as well reduce the need for corrosion protection?

I know there is a debate on bonding or not, and this is not the nature of my question, only whether the newer type seacocks introduce an additional type of corrosion risk because they contain 2 types of metals.

Thanks!
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Old 06-12-2011, 11:48   #2
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Re: Sea Cock Question

Im gonna take a stab at this , ( though I am no expert) and say I dont think so.
From my own experience Sealants even 5200 have had a tough time sticking very well to starboard. Someone may have a solution or better idea,.
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Old 06-12-2011, 12:28   #3
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Re: Sea Cock Question

1) I don't think Starboard is an appropriate backing plate due to the mentioned adhesion issues. You don't say whether the hull is glass or metal, however, which would affect my answer. If glass, I think the best course is to encapsulate plywood in epoxy, and then epoxy all that into place making the "pad" area about four times the area of the seacock base. Then, after drilling the hole slightly oversized, epoxy the hole shut in a manner very similar to how you do a hole in a cored deck properly. Then, drill through the epoxy. Now both pad and hull are isolated from the ocean by a "donut" of epoxy. Also do the same for mounting screws or bolts.

2) Yes, there is an issue with galvanism here, at least potentially, pun intended. The answer to bonding is "it depends". I recommend this book:

http://www.amazon.ca/Metal-Corrosion...3199557&sr=8-4



in order to fully understand the issues.

For instance, I have bronze seacocks on steel threaded pipes below the waterline that I will be swapping out for Marelon, not because I love Marelon, but because only being in non-electrified freshwater has kept me from having problems with corrosion on a steel hull.
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Old 06-12-2011, 12:45   #4
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Re: Sea Cock Question

Agreed with the above. The day they invent a good adhesive/sealant for "Starboard" it will be a good day indeed.
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Old 07-12-2011, 10:23   #5
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Re: Sea Cock Question

The Stainless or chromed ball does not touch the sides of the valve body. There is nylon rings/gaskets that the ball seats / rides on at the two ports. There is a contact point at the valve stem and ball. That is where the galvanic corrosion will happen and it is the weak point in the design. BTW stainless steel is preferable to chrome plated as the chrome will fail after a number of years.
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Old 07-12-2011, 11:49   #6
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Re: Sea Cock Question

Use Azek for your backing plate. www.azek.com/azek-sheet/

Use West Systemís - Six 10 Adhesive Thickened Epoxy Adhesive to bond it to the hull.
http://www.defender.com/product.jsp?path=-1|10918|12626|1414373&id=1152086

Drill and screw down the same as if you would use marine plywood.

Forespar Marelon Valves would be a better option if you are worried about bonding issues.
http://www.defender.com/product.jsp?path=-1|51|106370|813148|319675|860856&id=101939
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Old 07-12-2011, 16:35   #7
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Re: Sea Cock Question

The ancient all brass tappered seacocks are a maintance nightmare. To keep them in tip top shape the tappered surfaces need to be taken apart and throughly cleaned yearly. Cleaning can invlove a light lapping. That said the brass,stainless-nylon is the top of the line for a metal valve.
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Old 07-12-2011, 16:45   #8
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Re: Sea Cock Question

Quote:
Originally Posted by sailorchic34 View Post
The Stainless or chromed ball does not touch the sides of the valve body. There is nylon rings/gaskets that the ball seats / rides on at the two ports. There is a contact point at the valve stem and ball. That is where the galvanic corrosion will happen and it is the weak point in the design. BTW stainless steel is preferable to chrome plated as the chrome will fail after a number of years.
Ditto! And the stem should be floating on seals. Some brands of the better seacocks are using a plastic ball now (Acetate, I think). Acetate does not absorb water.

BTW the known brands are rebuildable, providing there's no galvanic problems. A kit will include a new ball, seats and seals.
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Old 07-12-2011, 16:46   #9
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Re: Sea Cock Question

Mark, I hope you meant bronze, not brass in post above.
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Old 07-12-2011, 16:59   #10
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Re: Sea Cock Question

Also, I think the seats are Tefflon not nylon. Nylon absorbs water and swells like crazy.
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Old 07-12-2011, 17:52   #11
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Re: Sea Cock Question

Thank you so much for the post regarding starboard,I am replaceing all my thru hull'ss as we speake cut starboard today,ready to install tomrrow,COTEMAR you saved my day,now to find azek sheet
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Old 08-12-2011, 09:53   #12
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Re: Sea Cock Question

Quote:
Originally Posted by sailorchic34 View Post
The Stainless or chromed ball does not touch the sides of the valve body. There is nylon rings/gaskets that the ball seats / rides on at the two ports. There is a contact point at the valve stem and ball. That is where the galvanic corrosion will happen and it is the weak point in the design. BTW stainless steel is preferable to chrome plated as the chrome will fail after a number of years.
True. I believe the nylon seat is often Delrin, and I've had a handle come off in my hand. Glad I wasn't in the water at the time.
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Old 08-12-2011, 10:10   #13
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Re: Sea Cock Question

Quote:
Originally Posted by shamrock View Post
I'm replacing a sea cock and deciding on a few things:
Sea cock? Ahem. I suspect you would be deciding on a few things.

I think you mean "seacock."
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Old 08-12-2011, 10:32   #14
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Re: Seacock Question

Here is some good information....

Seacock & Thru-Hull Primer/Pre Information Photo Gallery by Compass Marine at pbase.com
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Old 09-12-2011, 16:12   #15
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Thanks everyone for the great info!

Cotemar, Can you tell me more about azek? this stuff solves the sealant issue with Starboard?

Thanks!
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