Centerboard Cable Runs......?

[NYSail]

Hello all,I have a P36-2 with shoal keel/centerboard. The cable comes up through the hull into a ss base plate and ss watertight sheave housing (bronze 3" sheave inside), through bronze (or brass) pipe to another ss sheave housing turning 90 dgrees then through more pipe to another ss sheave housing then turning 90 degrees and then up to the deck. The pipes are connected to the sheave housings with threaded unions that are extremely corroded and will not budge. Have been soaking them for the past two weeks in pb blaster. Also, all this is below the water line. I have a slight leak at the base plate that the p/o kept putting 5200 ontop of.Obviously, the base plate has to be rebed. I have to dissassemble the system and figure I will just cut the tubes and remove everything and bring it home to take fully apart and inspect as it is 20 years old and never serviced.Question: has anybody else ever had to have water tight sheaves fabricated or had to deal with a similar situation with a centerboard cable run?Just looking for advise / opinions prior to cutting.Greg1986 P36-2

 

[RAD]

Greg,....

Looks like standard brass pipe and fittings,can you get a saw blade and make a cut on the union where it's threaded with out cutting all the way through and damage the threads on the part the union is threaded to,this way it will relieve the union and you should be able to unthread it. then replace it with a new one. another thought is to cut right thru the union and then try and unthread it from the pipes

 

[r.w.landau]

NY, if it is brass, I would replace it.

Chances are you will break the pipe at the fittings. This is what happens in plumbing lines in old homes. Being in salt water and the make up of brass ( brass is an alloy of copper and zinc) the zinc has probably been eaten away.The remaining copper is weak and will break at the weak point, the threads.If I were you I would keep the stainless (if it is in good shape) and replace the brass. Maybe with something else.I find it hard to believe that the brass lasted this long in the salt water enviornment.just an opinion.r.w.landau

 

[CalebD]

I think that r.w.landau might be onto something

something as the pipe in the photo shows a bluish dusty patina like oxidized copper. Not sure what color oxidized zinc is but I seem to think it is white. How many sheaves in the run to the cockpit are there? I could not figure it out from the photos.

 

[CalebD]

Forgot to mention

that to test SS for its condition, if a magnet has some attraction to it, it is decayed. SS is not supposed to be magnetic because of its alloys. If it exhibits any magnetism it is suspect.I want to test this out myself. Where is my magnet?

 

[CalebD]

Another hunch

after reviewing the photos I suspect you may have some mixed metals which can cause problems. The sheave case looks like SS while the fittings (nuts, bolts) really have a blue color to them. Is the CB tubing pennant hooked up to the battery ground with a zinc on the shaft or elsewhere? If not, it should be grounded with the engine (usually) so as to reduce the electrolysis that occurs when water is present around different metals and electricity. This requires a zinc to be attached to the ground below water level; usually on the prop shaft or wherever. If it is grounded then you need to keep an eye on it and try to open it up and check it out.PB Blaster works pretty well with some serious wrenches (or is that wenches?) after it soaks in. I assume you are on the hard so now iw the time to look into this. You will decide what needs to be done next.Fair winds and following seas.

 

[NYSail]

Two Sheaves and the base plate....

the photos are in order from bottom (1), then going up 12 " to the second sheave housing (2) then over 14" to the last sheave housing (3), then the brass tube runs up about 1' above the water line into a ss conduit heading towards the deck. The unit is not grounded and has no zincs. I have often wondered about that too...should it have a zinc? a ss pendant, ss sheave housing with bronze sheaves inside, and brass unions and tubing all under salt water sitting at a slip.....How can you tell the difference between bronze and brass. I was told the tubes are broze by some and brass by others. The unions also have been said are brass....I am metal ignorant.I was considering replacing the tubing with marine grade thick rubber hose and clamp it onto the ss sheave housings. The though of the cable cutting the rubber has come up, however, the cable moves very slowly when pulling the board up and not often. Also, the cable is always pulled taught with no slack to hit the sides of the hose. Using the hose would give me better access for future service, make a flexible run rather than the rigid fixed one that I have with the brass tubing putting less stress on the anchored portions of the run (where the sheave houses are bolted to the boat) and would cut out different metals being attached. What do you think?Thanks all for the wonderful input so far!Greg

 

[RAD]

Greg...

Do not put rubber!!, you'll create a huge problem when the cable cuts through and your off shore having a great time on vacation.Me thinks the pipe is fine and it just needs a new union to stop the leak.interesting thought about the grounding of the pipe.I would think it's grounded somewhere

 

[slip knot10761]

additional consideration

This is definitly a difficult and labor intensive job. I would suggest that you replace the ss wire and swaged attachments to the centerboard before splash-down. Although I'm now in fresh water[be back in salt water this fall] when I had a swing keel I made it a point to always replace the ss cable when I hauled out for whatever reason.It's easier to replace on the hard than wet. Also, being amettalurgist I would suggest using ss [304,316 grade] fittings and tubing in order to minimize electrolysis damage and grounding to zinc on the motor shaft. Below waterline events are not usually good. Your labor/time to do this job is much more than the additional cost of ss. Good luck.

 

[LloydB]

just a question

why not just convert to pvc conduit and fittings? it seems to me that any pipe designed to keep water in should also keep water out or is there some unmentioned reason for connecting the dissimlar metals with a conductor? BTW NYSail how many lbs of tension is at crank end of cable and what is usual for this boat?

 

[Ross]

What size wrenches have you applied to

this problem? 18 inch pipe wrenches will be the minimum to turn those fittings.Also the careful application of some serious heat can make a big difference. Shield the surrounding area with some flame proof material and heat the fittings with a torch and apply the wrenches while it is still hot.Gypsum wall board is as good as anything for the flame shield. McMaster-Carr sells bronze, red brass, and yellow brass pipe and fittings. I would tend to stay with bronze pipe in this application. Bronze has a better track record than stainless steel in a seawater environment.

 

[NYSail]

Tension

I am not sure the exact amount of tension, however based on the fact that the cable is attached to the top of the centerboard and that the centerboard is 4+/- feet long and weighs 200+/- lbs I imagine a lot! That is one of my concerns having so much tension on 20 year old sheaves that cannot be inspected, that have been underwater continually. If the sheaves breaks......down does the boat. Actually, I have already figured out my emergency repair if the housing breaks so I won't sink, but damn it could get ugly quick!The pvc sounds good also. It would be rigid enough not to have the cable run against it and would still be able to flex with the boat. I would have to figure out how to attach it to the sheave housing nipple so that it can be easily removed. Thanks....great stuff guys!!Greg

 

[NYSail]

Heat

Ross sounds good. I am going down Sunday morning (while out for my beer run for the game) and will put a torch on it. Also, I think I did under-estimate the wrench size. I will bring adequate tools and give it a try. I was just worried about beaking the ss threaded nipple. But I guess if I break it while taking it apart, it was no good anyway and needed to be replaced.?Thanks!!Greg

 

[r.w.landau]

I wouldn't use PVC.

Maybe ABS or I think that the grey electrical conduit has more flex.You can glue threaded fittings on it and if you are worried about rubbing, You can over size the pipe then at the threaded connections, reduce to the right thread using reducer fittings. Now you have to concider the glue....The more I think about it, the more I think that your existing is bronze. I would go back to it.The stainless cases look like they are in good shape and if the bronze sheeve goes, the stainless case will still be watertight.The operation of the centerboard should give some warning as to the sheeve going.r.w.landau

 

[NYSail]

Grounding

I have often wondered about zinc on this part. I am not sure how I would attach a zinc to the system. The zinc would have to be under water attached to the cable, right? I am at a slip with moderate electrolysis based on what my zincs look like at seasons end.Thanks!Greg

 

[Ross]

GREG, Take a fire extingisher with you,

CAN,T be too careful.

 

[r.w.landau]

I wouldn't heat things up too much, remember that

the stainless is connected directly to the boat. If you heat the union, becareful not to heat it so that the stainless becomes to hot.r.w.landau

 

[NYSail]

LOL

Great advise......One always sits in the box with my torch! I have seen some dumb stuff happen, especially from weekend guys like me!Thanks!

 

[r.w.landau]

Looking at the last sheeve before it goes to

the cockpit, the bracket that it is mounted on is a pretty big moment arm. My guess is the centerboard is fiberglass and less than 100#.r.w.landau

 

[NYSail]

My ignorance

I vaguely understand moment arm....Yes centerboard is fiberglass...weight, from what I have been told was approximately 200 lbs., but that may be hear-say. Makings a long story short I guess you are saying that there is not as much stress on this as I might think based on looking at the design?ThanksGreg