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Category: Power Boats
Asked By:
Richard Zucchi
Date:
18/04/2010
Boat:
Top Secret
Hi Fellows,
I have a 33-foot Egg Harbor SF motor yacht, 1984 vintage. Over the past 3 to 4 years I have been getting "halos" around metal underwater parts, i.e. struts, trim tabs, dinaplate, swim platform bracket. The electrolysis attacks and destroys the copper in the paint leaving the spots vulnerable to barnacles.
I've noticed that the problem is mostly on the port side and the large zinc anode on the port side is not decomposing. The Starboard side zinc is decomposing normally.
I use micron CRC bottom paint and I called Interlux and asked them for help. They told me to take all the metal down to bare metal and cote it with epoxy, which I did. That did seem to help on the starboard side, but I still have the problem to port.
I have been suspecting stray current from other boats in my marina, because I am the only one that seems to have this problem. The boat just next to me is fine.
Now I am suspecting that my boat may be the problem, especially since the port side anode isn't decomposing. How can I check the electrical system for stray current while it is out of the water, to determine if the problem lies with my boat? I have checked the bonding system and everything is OK. If I need to correct something, I'd like to take care of it while the boat is out of the water. Any help would be much appreciated.
I have a 33-foot Egg Harbor SF motor yacht, 1984 vintage. Over the past 3 to 4 years I have been getting "halos" around metal underwater parts, i.e. struts, trim tabs, dinaplate, swim platform bracket. The electrolysis attacks and destroys the copper in the paint leaving the spots vulnerable to barnacles.
I've noticed that the problem is mostly on the port side and the large zinc anode on the port side is not decomposing. The Starboard side zinc is decomposing normally.
I use micron CRC bottom paint and I called Interlux and asked them for help. They told me to take all the metal down to bare metal and cote it with epoxy, which I did. That did seem to help on the starboard side, but I still have the problem to port.
I have been suspecting stray current from other boats in my marina, because I am the only one that seems to have this problem. The boat just next to me is fine.
Now I am suspecting that my boat may be the problem, especially since the port side anode isn't decomposing. How can I check the electrical system for stray current while it is out of the water, to determine if the problem lies with my boat? I have checked the bonding system and everything is OK. If I need to correct something, I'd like to take care of it while the boat is out of the water. Any help would be much appreciated.
Answer:
"
Hi Richard,
This is an interesting problem, stray current is exactly that, it meanders wherever there is an electrical pathway. In other words it's not selective. The perplexing issue is that you say the port-side anode doesn't decompose, but the starboard-side anode does. You also state that the halos and corrosion on the metal underwater parts is worse on the port side where the anode doesn't decompose. This begs the question - - is there and a break in the electrical connection to the port-side zinc anode? That's where I would start.
Moving on, let's assume you've verified that the port anode has electrical connection, then we have to look a stray current sources. Preforming a stray current test is pretty simple when the boat is out of the water. Just take a regular voltmeter and attach the negative lead to the negative side of your service batteries, then touch the positive probe one at a time to the engine block, propeller shaft, your bonded system, keel bolts (if you have them), bow thruster casing (again if you have one), ans so on until you find the source of the stray current. With the boat out of the water the current should read very close to 0.0 Volts. If you do find a stray current then try to isolate it by switching off one at a time at the switch panel the various electrical appliances until you see the voltage disappear. Once you isolate the source, then you can trace the wires back to the offending item.
I recently had to do this on a new Swan 82 and managed to trace a stray current back to some faulty wiring in a compass light. I only took me about half a day, so it's a much less daunting task than it may seem.
However, the fact that your halos and corrosion appear more on the port side and the port side anode isn't decomposing at more or less the same rate as the starboard side suggests to me that the connection to the port side anode is damaged in some way or possibly severed.
Hope this helps. Good luck.
Captain Ian Fagg
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