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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 06-04-2014
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Centerboard line tube

Greetings again everyone. I wanted to throw this out for suggestions; our vessel is a Seafarer 34 with a centerboard. The centerboard trunk top is below the water line and the line that raises and lowers the board is also enclosed in a tube below the water line. I have ordered a specialty stainless steel alloy to fabricate a plate and elbow arrangement that will be bedded into the trunk top and act as the mounting point and final bend for whatever tubing material houses the line or cable. Originally the vessel had standard copper tubing but I do not want to use that because it will attach to stainless and I am worried about the electrolysis action with the two dissimilar metals. I have been considering a plastic like conduit as this will eliminate any corrosion threat. The tube travels aft approx 8' then makes two 45 degree turns to bring it to the cockpit. There are flexible conduit elbows that would be perfect. Does anyone see an issue with this or have a better suggestion. I would go all stainless but the alloy I am using is super expensive and other less expensive options are subject to crevice corrosion. I would be threading the conduit elbow together and am still looking into an adhesive, or perhaps West System G Flex at all joints? The control line will most likely be Dyneema. I have considered all other metals and plastic seems like a viable option here. Unless someone can tell me 316 stainless is a good idea I don't know what else to do?
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Old 06-04-2014
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Re: Centerboard line tube

PEX tubing for the long run aft?
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Old 06-04-2014
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Re: Centerboard line tube

The tubes on our old Bristol are fiberglass. I have no idea what they formed the f/g over, I would guess copper tubing based on how the boat is built, but you could use some form of plastic since it really only a form. The sheaves where the cable turns are bronze with the axles just set into f/g. Seems to have worked since the boat is more than 30 years old. I am planning to cut into the sheave housings and replace the sheaves just because it is so old. May also switch from ss cable to high tech line.
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Old 06-04-2014
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Re: Centerboard line tube

FRP tubing...
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Re: Centerboard line tube

fiberglass tubing would be fine if I could find some 45 degree elbows. ABS plastic is an option but not a great one. So we are in agreement that copper is a bad idea? Even if between the copper tubing and the stainless box there was a plastic coupling to isolate the copper? It's hard to find info on this, but I know that copper bronze with any amount of zinc in it is a bad idea. Perhaps ABS plastic with phosphor elbows, they should all be pipe fitting interchangeable.
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Old 06-04-2014
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Re: Centerboard line tube

The elbows on my boat are also f/g. I have no idea if they built the assembly on a bench or built it in place on the boat, but it is all f/g below the level of the cabin sole. Above this it is 1" stainless tubing that acts as a handrail at the front of the galley.
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Old 06-07-2014
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Re: Centerboard line tube

I like the idea of integrating the handrail, I'll keep that on my mind. I've been looking into this more and more and have two options as I see it. From the threaded piece of 1/2 pipe at the box mounted above the truck I can go rigid, or flexible, we've gone over this. Here are the pro and cons. For rigs, I could use Schedule 80 PVC, its cheap and would thread onto the pipe with an equally thick coupling and be run back to the cockpit through two 45 degree couplings, all threaded, a total of six possible leaks. The other alternative is going with a semi flexible tube, and using a compression fitting that adapts to the 1/2" pipe at the box. This has the advantage of a continual smooth run and one connection with only two possible below then waterline leak points. The compression fitting would be plastic, PVDF to be exact to avoid galvanic issues between stainless and bronze. Does anyone see an issue with setup number two? I will order a few of these compression fittings to test them out, probably with a hammer and some extra hard wrench abuse to see what they can take before failing. If they hold up then I think this might be a very viable option. If there is ever a leak I would know instantly where it is, I will have direct access to the box and compression fitting under the sole. Sorry if this is simply a recap of this entire post to date but I wanted to lay out two clear options with the pros and cons. The flex line might give up some strength over sch. 80 pipe but then again, how much force are we talking about. It's like a giant bike brake cable really. Thanks for the input!
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Old 06-08-2014
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Re: Centerboard line tube

Is the cable you are using going to rub on the PVC 45 deg. elbows? If so, it will wear right through, like a saw. In a short amount of time.
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Old 06-08-2014
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Re: Centerboard line tube

Also be aware that if your tube is going to be firmly attached to the center board casing you may have problems if you also try and firmly attach it to the cabin roof.

My tube is stainless steel and on passage it is clear the cabin roof moves a little breaking the seal. I am considering incorporating some kind of lip seal when I redo this.
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