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Old 03-06-2010, 20:45   #31
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DeepFrz - I agree that aluminium and bronze don't mix well, but in this case I think it would be OK since the two would be totally isolated electrically from one another. Not that I am recommending bronze seacocks for Viribus. I was simply pointing out that he would be able to use any seacock material of his choice.
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Old 03-06-2010, 23:11   #32
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Originally Posted by ViribusUnitis View Post
Can you describe this arrangement to allow yourself to replace the seacock with ease better? I can't seem to picture it in my head.
This is called standpipe (extends above waterline inside vessel) and is a classic security feature.. if you google around for standpipes and seachests (similar concept) you should be able to find some pics and descriptions
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Old 04-06-2010, 05:16   #33
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A solid and strong plastic coupling between the standpipe and the seacock would accomplish two things:
1. the seacock is now isolated electrically from the standpipe, reducing risk of corrosion, and
2. This would allow you to use ANY seacock, including bronze, stainless, etc. - your choice
.
I understand that theory, but from what I have seen of aluminum boats I would not voluntarily introduce another metal under water, even if it is 'isolated'. I have learned that nothing is ever truly 'isolated'. Dirt and salt crystals can create an electrical path, some bit of metal may accidentally lean on the piece, and I have heard that you can get current loops right in the salt water. In any case, in the real world, I have seen some of these 'isolated' fittings that were perfect after 20 years but enough others that had corrosion problems that I would be reluctant.

In theory I think the marleon on flanged stand pipes is perfect, so long as the construction quality of the seacocks was high. My problem is that Forespar seems to have let their quality slip, and we need a good new competitive supplier. From a theory point of view, the only real risk with Marleon (on flanged standpipes) is fire. They are mechanically pretty strong but will melt and burn at high enough temperature. The super yacht refit I was project managing was getting commercially certified and could not use plastic because of the fire risk. After much discussion with 'experts' we ended up using stainless valves insulated from the aluminum.
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Old 04-06-2010, 05:36   #34
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Nitpic,

I don't know if I'm the only one but I can't see your pictures.
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Old 04-06-2010, 06:46   #35
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I don't know if I'm the only one but I can't see your pictures.
+1
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Old 04-06-2010, 07:10   #36
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Originally Posted by DeepFrz View Post
I bow to your experience Brent. Was the plastic through hull that you removed Marelon?
Marelon (R) is NOT plastic (that's like calling epoxy "plastic"). From Forespar's website (http://www.forespar.com/MarelonPlumb...lonAbout.shtml):

About Marelon®



Marelon® is a proprietary formulation of polymar composite compounds using composite reinforced polymer and additives to produce a superior marine-grade product.
  • For use above and below the waterline
  • Precision molded plumbing systems
  • Complete freedom from corrosion
  • U.L. and A.B.Y.C. approved
  • Forespar "93" series valves and thru-hull fittings meet all design criteria and exceed all mechanical property requirements specified by the International Standards Organization
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Old 04-06-2010, 07:25   #37
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Thanks David. Yes I knew that. I was just trying to get clarification from Brent, but I guess he isn't going to answer the question.

There are cheap plastic through hulls on the market. I don't believe they should ever be used on a boat, but they are.
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Old 07-06-2010, 17:21   #38
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Deepfrz, guess you left your sense of humor at home today. It was meant in jest. If you have ever seen Babylon 5, you would understand the reference.

Brent, what filler did you use when doing the weld?


Sabre
I stick weld with 316L rod. Welding pipe nipples in eliminates the surface between the flanges and hull to worry about . You can see everything anytime. I've been out cruising, away from the internet, altho I don't make much effort to visit these right wing biased sites anymore.
The plastic thru hull I kicked off was not marelon. With marelon, I would have had to kick slightly harder. It would take some serious swinging with a sledgehammer to break a stainless nipple off. Maraelon is flimsy compared to a stainless sch 40 pipe nipple welded in, with a stainless ball valve.
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Old 07-06-2010, 18:20   #39
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Deepfrz, guess you left your sense of humor at home today.
Its a good place for it to be, right here at home with me.
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