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Old 14-03-2007, 16:34   #1
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When should thru hull fittings be replaced?

I have been changing hoses, valves etc. and I started wondering if my thru hull fittings should be replaced. Is there a way to tell? From what I can tell mine are good but I do not know how long they have been in the boat.
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Old 14-03-2007, 20:00   #2
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My catamaran had marelon/synthetic through hulls, and two of them broke while I was in the bilge. One was for the cooling system water intake in the engine compartment and the second was for the head intake. One broke when I was out of the water in the boat yard, and the other broke off while I was working in the bilge, and an immediate gyser of water squirted into the boat. I quickly put my finger in the hole in the hull, and then I put a bung in the hole.

After that episode, I got rid of all of the marelon through hulls. I ended up changing all the through hulls while the boat was in the water. That was an exciting experience. I had a friend working on the inside of the boat while I was on the outside with a wet suit on. I had beached the boat, so it couldn't sink if something went wrong, but all the through hulls were still under water when we changed them out.

Now I have all bronze through hulls. The big marelon through hulls seemed immensely strong, and the smaller size ones seem to be the biggest risk for breakage. In both cases when they broke, it was only a minimal bump to them that broke them off. Incidently, the first one broke when the boat was four years old, and the second broke when the boat was nine years old. So if you have marelon through hulls, those small ones should be changed out frequently in my experience. Better yet, change the small ones to bronze.
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Old 14-03-2007, 20:05   #3
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All of mine are bronze and could be 25 years old, I have no way of knowing.
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Old 14-03-2007, 20:21   #4
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Calculate, inspect, service...

First I would suggest calculating the age of your boat.

Then inspect your through hull fittings. There should be clues. If they are all of the same type then they may have been installed when the boat was new. Through hulls have fashions and styles. You may know when a particular style was in fashion, or your friendly marine expert may know.

Now consider their condition. Some may appear to be in better condition than others.

Also check their fastening(s). You could give each one a very gentle wobble. Look for leaks.

If all appear to be in good condition and you are still worried then I would suggest replacing one or two at each haul out.

This would be a good time to replace hoses and hose clamps.
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Old 16-03-2007, 16:39   #5
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Quote:
Originally Posted by maxingout
My catamaran had marelon/synthetic through hulls, and two of them broke while I was in the bilge.
From your description, it sounds like they just spontaneously failed, and it was lucky you were there to see it happen. Is that accurate?
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Old 16-03-2007, 16:57   #6
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IS, If the valves don't leak and the handles work easily then they are probably still in good shape. But check to be sure that they seal and close completely with the hose off. If any of these are a problem consider replacement, otherwise save your money. We have a few that are 27 years old, still in great condition and I have no concerns with them. But we do service them regularly. Also look for a pink or reddish color. This is a sign of electrolysis. green is of no concern. "If it ain't broke don't fix it".
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Old 16-03-2007, 17:00   #7
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Anyone one know if the following is B.S.? I got these from old timers.

Scratch the fittings, if it is yellow/gold color it's good, if it is pink the alloys leeched out (electrolysis or whatever) and needs replacement.

Everytime this one guy hauls, he gives them a rap with a hammer. I've actually heard two versions of this. One is you can hear the difference between a good and bad fitting, the other is if it shattered it was bad.


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Old 16-03-2007, 17:36   #8
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Quote:
Originally Posted by coot
From your description, it sounds like they just spontaneously failed, and it was lucky you were there to see it happen. Is that accurate?
The through hulls were just barely bumped when they broke off. It wasn't as if hoses were being forced onto the through hulls shearing them off under great applied stress. A hand bumped up against the through hulls and they were history. It was really scary to see how easily they broke off. The large synthetic through hulls all appeared to be in good shape, but I changed them out anyway.
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Old 16-03-2007, 20:53   #9
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Aloha Maxing,
Really would like to hear more about these through hulls. Were they the plastic ones like they sell in West Marine or real Marelon?
Very scary. Don't want to install the wrong thing.
Kind Regards,
JohnL
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Old 17-03-2007, 02:55   #10
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John:
Yes, your old-timer has it about right.

The “alloys leaching out” of copper-based alloys, such as (manganese) Bronze, is called De-Zincification, resulting from Galvanic Corrosion.
The first symptom of dezincification will usually be seen as bright, clean, red or pink patches on bronze fittings, caused by the surplus of copper which is left behind. These are mostly easily spotted shortly after lifting out, and before the metal becomes dulled (by oxidation).
Electrolysis, or stray current corrosion is usually notable by the very bright appearance of the corroded metal. When the pitted part of the metal is bright, that means that the corrosion is so rapid that oxides have no chance to form. That's particularly true with all copper-based alloys like brass and bronze.
When the surface is dull, but still brightly colored such as pink or orange, this tends to indicate a less rapid rate of corrosion, but stray current nevertheless.

Apart from these visual indications, try sounding the fitting with a hammer. Dezincified bronze often has a 'dull' sound - though not always, so treat this only as an indicator.
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Old 17-03-2007, 05:16   #11
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Everytime I do shaft work on a boat with a pink color to the underwater gear. the nuts will fracture and the end of the shaft powders under pressure to get the prop off.
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Old 17-03-2007, 07:55   #12
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You can't over tighten Marelon or it breaks.
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Old 17-03-2007, 17:49   #13
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maxing what Tnfkakbait said! if your thru hulls were real marelon that should not have happened unless the fitter was over zealous when installing them. it sounds like you have either fake marelon or a mfg. defect with yours. real/properly cast/extruded marelon should not behave like that.
Irwinsailor as Gordmay said. my thru hulls are 28 yrs young and show no signs of a problem, just green corrosion where salt water/air/vapor has made contact. i had two cockpit drain thru hulls change color. these are at the water line, but this was caused by ez-on ez-off (acid hull cleaner)
all my thru hulls are bonded ?mark if this good or bad, but this the way i $$$ the boat. i don't know if they were factory bonded or after the fact. i did pull the two cockpit thru hulls, because they had gate valves and the surveyor said to get rid of them, anyway like i said these thru hulls as everything else that is open under neath the waterline are all in very good condition. the only caveat being i am on a mooring in a river with a 6-7 knot current, where you would have less chance of stray current from other boats.
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Old 17-03-2007, 20:57   #14
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Quote:
Originally Posted by mike d.
maxing what Tnfkakbait said! if your thru hulls were real marelon that should not have happened unless the fitter was over zealous when installing them. it sounds like you have either fake marelon or a mfg. defect with yours. real/properly cast/extruded marelon should not behave like that.
The two through hulls that failed were installed by the manufacturer of the yacht when it was in the factory. They were original equipment. Perhaps they were over tightened when installed. I don't know. I do know that two of them broke off with minimal manipulation.
As best I could tell from looking at the through hulls, they were all real marelon. I can imagine that an overzealous installer could easily over tighten them at the time of installation.

Cheers,

Dave
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Old 18-03-2007, 02:16   #15
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If you have reason to suspect* corroded immersed metals, it might be a good time for a corrosion survey, as discussed at “WARNING: change when half worn”
WARNING: change when half worn.

* See David Pascoe’s excellent article:
Corrosion: Buying, Owning and Maintaining Boats and Yachts

and:

ABYC Section E-2 - Cathodic Protection
http://www.abycinc.org/committees/E-02.pdf
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