Testing slip for current- Zincs gone in 7 weeks

[Streff]

How does one test the water around the boat for escaped current/short?. I read several articles about bonding, zincs, etc but nothing came up about testing the slip.

The PO had the boat in fresh water. For what its worth, the survey did not indicate that there is a short on the boat. We moved the boat to a saltwater marina, and since then we have changed the zincs 3 times in 12 months. Changed zincs in late March, now they are almost gone (7 weeks later) especially the thrusters. Our slip is right next to a large distribution electrical box. Had a chat with the marina and they recommended testing the water around the boat.

One diver says that he has seen it before with electric distribution boxes.. but all cables from the box travel within the concrete dock, so there is that.

Any ideas or guidance on how to test the water around the boat would be greatly appreciated.

Thank you in advance

Streff

 

[Larry M]

I’d get a corrosion analysis done by an ABYC certified corrosion tech. He’ll check your boat and the shore power looking at the bonding system, stray current, grounds, etc. We had one done a few years ago. It took him about an hour with me helping. Here’s a link that should help you find one for your area or ask the local boat yards who they use. I would make sure the tech is ABYC certified though regardless. Good luck hunting down the demons.

https://abycinc.org/mpage/findatech

 

[Comodave]

I’d get a corrosion analysis done by an ABYC certified corrosion tech. He’ll check your boat and the shore power looking at the bonding system, stray current, grounds, etc. We had one done a few years ago. It took him about an hour with me helping. Here’s a link that should help you find one for your area or ask the local boat yards who they use. I would make sure the tech is ABYC certified though regardless. Good luck hunting down the demons.

https://abycinc.org/mpage/findatech

+1 absolutely.

 

[Redhook98]

Concur with above. But, you can also buy a silver-silver chloride anode and test your own system. With that, you can isolate if it is your boat, your neighbors and/or what could be the cause of this on your boat. You have to have some troubleshooting skills though. Do you have galvanic isolators installed for your shore power?

 

[DDW]

Just a random thought, I assume you are using zinc anodes and not magnesium (as you would for fresh water)?

 

[EngNate]

See post #5 and the attachments here about galvanic and stray current testing.

You do not need an expensive reference probe, these have been unnecessary since the advent of digital multimeters. Make a probe from a zinc pencil anode, it doesn't have to be fancy, wire with a ring terminal, attached with a nut. Test the water around your slip by testing the dock ground (outlet box metal) with the probe in different places.

If your boat was in fresh water it would have required magnesium anodes for effective protection. If moved to salt water these will react aggressively and go away quickly. Be sure that zinc or aluminium anodes are used now. I recommend AL, higher level of protection, last longer, more environmentally friendly.

 

[Streff]

Thank you all for the great input and comments. The anodes are Zincs.. I tried AL for the divers dream and it was eaten up just as quickly. But I do like the idea of AL.

I have a reference/testing anode ready to order from the online Zinc guys. Tried Amazon & other fast shipping online outlets but could not find a user friendly option.

Thank you EngNate for the info, I will certainly start with that testing today and see what I find.

As a side note, I had an electrician change all the outlets on the boat from the old dark brown from 30years ago to modern white outlets as well as adding GFI where needed based on the purchase survey. Yesterday, I checked them all with a probe and 2 of them has a Hot/Neutral reversal light up. They are in series with other outlets. So the crossed wiring can be anywhere. I am not sure if that could influence the stray current situation.

I found a couple of ABYC electricians in the area. They are booked up for a couple of weeks. Hopefully I can fix a few things in the meantime.

Thanks again

Streff

 

[cks]

We made a jig to detect stray voltage. The set up is attached. We use a dinghy and drape the assembly over the pontoons so the small plates are in the water.

Once increased levels of voltage is detected, we turn remove the power cords to one boat and measure again. We also then remove the plugs ( one boat at a time) of the adjacent boats as sometime the detected voltage is not where you think it may be.

A good DMM with resolution and sensitivity can measure small changes of voltage (low millivolts). We do this multiple times of the year. We have found a few increased levels close to boats and determined this to be a source of stray voltage.

 

[tiltrider1]

I would like to know if you have a Galvanic Isolator on your boat. Does your marina use steel piling? With out this knowledge I can’t tell if you have a power leak or if your zincs are protecting other boats in the marina. Disappearing zincs could have many different causes.

 

[Streff]

I do have a galvanic isolator it looks about 25years old) and the marina has a combo concrete/steel pilings. I am not sure how to check if the galvanic iso still works as expected but I will research it. I may also just buy a new one.

I am planning a haul out next week. I will change the zincs myself saving the $4-500 for the diver. That will be the 4th set of Zincs in 13months.