Corroded Dezincified Hose Barb on Raw Water Intake Ball Valve

[Dean Strong]

I recently discovered the hose barb threaded into the raw water intake ball valve was almost gone. The hose got bumped while changing the primary fuel filter in the same location. The hose began to leak, a turquoise liquid, and when I tightened the clamp, it got worse. Pulled the hose, and the barb broke clean off. The zinc had clearly leached out the bronze fitting, with patches of pink copper showing is several areas.

I was able to secure another barb (we were cruising in the San Juan Islands, WA), but am now very concerned about what else is corroding. One theory that has been suggested is that it was just natural corrosion from salt water in the hose between the closed valve (which I keep closed except when running the engine) and the sea water strainer. Since the valve is normally closed, it is cut off from any benefit the shaft zincs provide, which protect the prop and strut. It has been 11 years since the hose was replaced (yes, I inspect often, and this is hose is not subject to any kind of heat or UV exposure, so the hose doesn't war).

Any thoughts or similar experiences with galvanic corrosion in this area?

 

[colemj]

It is very common for people, and even boat builders, to use hardware store barb fittings on thruhulls. Often, these will be brass and not bronze, and will eventually corrode like you describe.

If your seacock is not corroding, then I'd just replace the hose barb with a real bronze one and call it good.

Mark

 

[Ralph Johnstone]

As per above, inferior metallurgy is the most likely cause of the early failure of the barbed fitting.

Kind of hard to tell what the history on that fitting is (was) given that the boat stopped production in '94. Don't know if it's an original fitting or replaced or whatever ? I can say that my boat's production run had all rough cast bronze fittings wherever sea water is encounterd.

As I expanded the number of fittings in my raw water circuits within the boat, I inserted a number of new fittings but not from a marine supplier. I chose to go with the heavier brass fittings offered from a major industrial manufacturer, Fairview Brass.

I have inspected the interior of many of these fittings after several years in service and found no signs of corrosion deposits or metal loss. Scraping a thou or two off of the interior surface with a sharp Exacto knife always reveals a bright yellow brass parent metal. With their increased thickness, I think they'll hold as long as I'm kicking around the boat.

As far as your current situation goes, I wound recommend eventually dismantling every bronze/brass fitting on the boat and give it a rub on the fitting interior and on the exterior of the barb, under the rubber hose to see what the parent metal looks like.

Since the valve is normally closed, it is cut off from any benefit the shaft zincs provide, which protect the prop and strut.

Close but no cigar. You need an electrical connection between the fitting and any zincs to achieve cathodic protection.

 

[Don S/V ILLusion]

When I used to winterize the A/C on our Hunter, I would suck antifreeze through the hose attached to that thruhull which was the only reason I noticed one year similar corrosion on the barb. The A/C and plumbing and thruhull were all DIY so it was my fault for using the wrong materials. Replaced with a bronze fitting and the problem never recurred.

 

[dlochner]

Since the valve is normally closed, it is cut off from any benefit the shaft zincs provide, which protect the prop and strut.

As @Ralph Johnstone mentioned there needs to be an electrical connection between the anode and the hose barb to complete the circuit. Although you have closed the valve, there is still water above and below the valve, this does not break any electrical connection. If current is going flow through this through hull, it will flow through the water, then the metal around the valve and the valve itself and then through the wire connecting the fitting to the shaft and anode.

 

[BigEasy]

I recently discovered the hose barb threaded into the raw water intake ball valve was almost gone.
Any thoughts or similar experiences

You have fittings over 30 years old of unknown quality & condition. Time to replace all of them with quality bronze fittings. I order replacements directly from Groco with BSPP threads on the thru hull, valve , & tailpiece to eliminate potential problem associated with nps/npt mis matched threads. You can also refit using Groco’s adaptor plate that is the next best thing to a true seacock (See @Maine Sail’s report on thru hull fittings). Whatever the source, whether galvanic, inferior alloy, or age it is time to address all the fittings immediately.

 

[Dean Strong]

Been searching on @Main Sail but nothing comes up. Is this Main Sail on Sailboatowners.com or some other site?

 

[kappykaplan]

Been searching on @Main Sail but nothing comes up. Is this Main Sail on Sailboatowners.com or some other site?

Here's the link (and it's @Maine Sail) :

About - Marine How To

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www.bing.com

 

[kappykaplan]

And here's the direct link to Plumbing:

Seacocks, Strainers & Hose Clamps Archives - Marine How To

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