Stray marina electric currents?

[Malbow42]

Three weeks ago my 89 year old John Alden designed cutter sank in the marina. After she was refloated we found the bronze through hull transducer had failed. The threaded section through the hull had corroded somewhat but still had about 2 mm thickness, but that section had broken away. The outer flange had parted, allowing water pressure to force the rest of the fitting inside the hull. I keep an anode hanging in the water with a wire attached to the rudder post, hoping to attract any stray currents. Three other through hull fittings are in good condition.
The only conclusion we can reach is a stray current targeted the fitting & caused it to fail quite quickly.
The boat is sadly a write-off. All the internal timbers have swelled & of course the engine & electrics are gone. The boat was immersed 22 hours by the time we refloated her.
i don't know what the answer is - maybe hanging 3 or 4 anodes over the side, keeping them clean to be effective, & perhaps replacing fittings each time the boat is out of the water?

[boatpoker]

How old was the throughull ? 89 yrs is a lot to ask of any metal in salt water.
If it was stray current, 99% of the time your own boat is the cause.

[Wotname]

Very sad to hear about the sinking of your cutter.

I would of thought the hull (and engine) could be saved but at what cost???

[Malbow42]

The bronze through-hull was only 11 years old.
The hull is OK but below in the cabin is where the water has done its damage. A major project to rebuild.
22 hours immersion of the engine & corrosion of all machined surfaces had started leading to corrosion cracking in the future.

[maxingout]

When I was in New Zealand, I saw a catamaran that had to replace both rudders because leakage current had severely pitted the rudder posts to the point of breakage.

I got under the multihull and touched the sail drive and felt the tingling of ac current on the sail drive. I went and got my volt ohm meter and measured 80 volts ac between the ground and the sail drive. I was lucky not to get electrocuted by the leakage ac current.

So that boat had dc leak that destroyed the rudder posts and ac leak coming out the sail drives. Very weird.

That's one reason I don't like to be in tightly packed marinas because I don't know who is putting what in the water and how it might affect Exit Only.

[foufou]

I have seen an engine under water for one week, rinsed with fresh water, oil changed, carburetor cleaned and started and run reliably. I don't know if that is always the case but have seen it before

[David M]

I have salvaged two outboards that were in the drink for a few days. I would not give up on an engine that has been submerged for only 24 hours.

[a64pilot]

Originally Posted by David M

I have salvaged two outboards that were in the drink for a few days. I would not give up on an engine that has been submerged for only 24 hours.

They Key is to get to it as soon as it comes out of the water, if it’s been dry for a couple of days, it is in much worse shape than it was as soon as it came out of the water.

[deblen]

If your transducer had a temperature sensor built into it,I would suspect salt water penetrated to the temp. sensing chip,which is fed 5vdc from the display. This will cause rapid & total destruction of the bronze t- ducer & other gear.

I ran into this when built in temp sensors began to be included in Airmar & other(B44V?,etc ) t-ducers back in the late '80's & used by various electronics mfgrs.

My solution back then was to cut the 5v feed at the t-ducer jack & live without surface water temp-which was not of much use anyway.

+5v hanging in the water does a quick number on underwater gear.

I don't know if the problem was ever cured or not,but it is something to keep in mind if you have water temp display on any gear.

Len

[SecondBase]

Originally Posted by deblen

If your transducer had a temperature sensor built into it,I would suspect salt water penetrated to the temp. sensing chip,which is fed 5vdc from the display. This will cause rapid & total destruction of the bronze t- ducer & other gear.

Len

Sounds like another reason to stick with my Milwaukee Tools remote temp sensor- plus it is good for checking engine spot temps as well as cooking.

[seabreez]

Originally Posted by foufou

I have seen an engine under water for one week, rinsed with fresh water, oil changed, carburetor cleaned and started and run reliably. I don't know if that is always the case but have seen it before

We had a tugboat under water for seven weeks in fresh water and when the salvage was done we started both engines a week after the haul out and both motors started. Both were 370hp Isuzu engines and today, they are still running strong, no issues.

Was your motor in fresh water? and was it diesel?

[SecondBase]

And I think this brings us right back to Marelon fittings which Mads @ Saillife selected. Does the diety of the ABYC rules sometimes prevent one issue but enable another?

Over the past 10 years have more boats (proportionally) gone down due to side loads on Marelon vs the "seems more frequent" galvanic corrision of metal?

[a64pilot]

I don’t have plastic thru hulls myself, but I’m led to understand that they are hell for strong, tested to something like hundreds of lbs of pull on a side load?
From my understanding it would almost take a sledge hammer to bust one off.

[deblen]

Originally Posted by Malbow42

Three weeks ago my 89 year old John Alden designed cutter sank in the marina. After she was refloated we found the bronze through hull transducer had failed. The threaded section through the hull had corroded somewhat but still had about 2 mm thickness, but that section had broken away. The outer flange had parted, allowing water pressure to force the rest of the fitting inside the hull. I keep an anode hanging in the water with a wire attached to the rudder post, hoping to attract any stray currents. Three other through hull fittings are in good condition.
The only conclusion we can reach is a stray current targeted the fitting & caused it to fail quite quickly.
The boat is sadly a write-off. All the internal timbers have swelled & of course the engine & electrics are gone. The boat was immersed 22 hours by the time we refloated her.
i don't know what the answer is - maybe hanging 3 or 4 anodes over the side, keeping them clean to be effective, & perhaps replacing fittings each time the boat is out of the water?

Folks
I may be wrong but I think the OP is telling us his depth finder bronze thru hull transducer failed,but three other "seacock" thru hulls are fine.
So,why would corrosion pick on just his depthfinder transducer??. & leave his seacocks alone?? See my earlier post for one possibility that I personally experienced on several vessels that I serviced.

Len

[Tellie]

What a shame and heart breaking when the phone rings. More boats are sunk at marinas than off shore. Marinas are well known for stray currents. Boats left and hooked to shore power at Marinas should have healthy bilge pumps. There are simple alarms that can send a message to your phone that your boat is taking on water. Agree as well, don't give up on the engine quite yet.