A question for the electrical gurus. - SailNet Community
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post #1 of 8 Old 12-06-2012 Thread Starter
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A question for the electrical gurus.

Could running a generator and sharing the power with another boat cause electrolysis?
At work I have a customer who has self installed a 30a shower power outlet connected to his generator. He uses this to share power with other powerboats he's rafted up with while on vacation.
No protection or isolation of any kind.

Props, struts and drive shaft were badly corroded on the port side, starboard showed minimal corrosion, perfectly acceptable.
new shaft going in, as a result of the large pits and defects. It ate away the bolts on the line cutters on the shaft so much that the heads were essentially gone requiring it to be cut apart.
I'm looking for potential sources, my boss has asked me to research the issue and write up a bit of a paper for the customer on both the risk, and the potential harm to the boat.
I'm hoping to do a really good job, since my boss is going to pay for my ABYC certification in the spring, and is looking for me to show some effort and initiative in figuring this one out.
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post #2 of 8 Old 12-07-2012
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Re: A question for the electrical gurus.

Electrocuting swimmers and carbon monoxide in the cabin might be worth worrying about. Thanks. Steve S.
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post #3 of 8 Old 12-07-2012
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Re: A question for the electrical gurus.

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Originally Posted by Jgbrown View Post
Could running a generator and sharing the power with another boat cause electrolysis?
At work I have a customer who has self installed a 30a shower power outlet connected to his generator. He uses this to share power with other powerboats he's rafted up with while on vacation.
No protection or isolation of any kind.

Props, struts and drive shaft were badly corroded on the port side, starboard showed minimal corrosion, perfectly acceptable.
new shaft going in, as a result of the large pits and defects. It ate away the bolts on the line cutters on the shaft so much that the heads were essentially gone requiring it to be cut apart.
I'm looking for potential sources, my boss has asked me to research the issue and write up a bit of a paper for the customer on both the risk, and the potential harm to the boat.
I'm hoping to do a really good job, since my boss is going to pay for my ABYC certification in the spring, and is looking for me to show some effort and initiative in figuring this one out.
JG,

I would suspect a DC corrosion issue. DC corrosion is MUCH FASTER and is, in most cases, caused by your own vessel. People often attribute heavy corrosion to AC leaks but this is highly improbable.

You should to start with the "bonding wires" or the copper wires either bare or green that are connected to all the underwater metals like the seacocks, struts, engine, rudder posts etc. etc... Insert a DVM on the "amp" setting, into a green wire, closest to the battery bank, and then begin firing up components and watching the DVM. It is significantly to have a high sensitivity AC/DC clamp meter like the Extech or Amprobe shown below to trace these down, as it makes it far easier..

With that amount of corrosion it is likely you have an on-board device using the bonding or earthing circuit to pass current, which should not be. This vessel should also have a galvanic isolator or isolation transformer. If there is a galvanic isolator it should be tested to make sure it is functioning.

You will also want to plug into the shore power and put a very sensitive AC clamp meter (must read to the hundredths 00.01A and have decent accuracy at low current) around the entire shore power circuit. Now turn on your AC devices one at a time, water heater, microwave, fridge, battery charger etc. etc. and see if you get a reading.

If you get any current reading on the shore power cord then you have a leak.. With the meter clamped around the cord the reading should be 0.0.. If you start seeeing 0.02 - 0.4A you have a leak and current is taking the green wire. This is often just bad connections or corrosion on the other side of the circuit causing current to flow back on the green wire but it culd be a faulty battery charger, water heater or other on-board device or a chafed wire shorting to ground somewhere.

If you don't have a clamp meter than you'll need to insert a standard DVM into the green/ground wire. There should be no current on this wire..

Here are two suitable clamps for measuring corrosion level leaks on boats:

Extech:
380942 - 30A True RMS AC/DC Mini Clamp Meter


Amprobe (A Fluke Company)
LH41A AC/DC Low Current On Clamp Ammeter | Amprobe


Complete those tests first, then we'll get you to buy more tools....
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Last edited by Maine Sail; 01-08-2013 at 07:31 AM.
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post #4 of 8 Old 12-07-2012
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Re: A question for the electrical gurus.

I'm not a guru, but I do have internet

The major difference using a portable generator is it is not grounded like shore power is supposed to be.
Nor is it grounded to the boat, so the real issue is the boat's systems - not the use of the generator.

While his boat might be perfectly grounded and not the producer of stray current one of the other boats might not be so well done.
That doesn't necessarily mean he and this are the cause - this sounds more like pier side issues because it's on one side primarily (unless he always rafted up on the same side, unlikely). Electricity flows in the shortest path to ground.

That kind of damage to stainless means long term exposure, not a couple of weekends at a raft up. Aluminum can be affect quick and hard, not stainless.
I'll never understand the current trend to sail drives of aluminum.

If another boat at the pier next to him is leaking and he's there for weeks, well there you go.
Of course it could also be a problem with the marina's ground for shore power; the only way to find it is to take a very sensitive meter and a lot of in the water measurements.

Here's a nice article on the subject - you have to read down in it for the electrical part.
BoatUS - BoatTech - Types of Marine Corrosion

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post #5 of 8 Old 12-07-2012
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Re: A question for the electrical gurus.

Dang it MS you type to fast

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post #6 of 8 Old 12-07-2012
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Re: A question for the electrical gurus.

jg, what Mainesail said.

But yes, once that fellow connects his genset to the other boats, now ALL of the boats and all of their wiring are part on one circuit, and if there's just one fault in any one of those boats, it can affect all of them, since they now have to be treated as one circuit.
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post #7 of 8 Old 12-08-2012 Thread Starter
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Re: A question for the electrical gurus.

Thanks :-) Will let you know how it all turns out.
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Re: A question for the electrical gurus.

Mystery solved. Customer disconnected bonding wire on that side from the zinc. Doh!
So everything on that side was nicely bonded to itself, just not to anything else.

When the customer heard that the wire was disconnected he was pretty unhappy, it turns out a diver was spinning the bolt about a year ago. He went down with a wrench, and some vise grips pulled the bonding wire and grabbed the bolt, then forget to put the nut back on again later. Expensive lesson.

Last edited by Jgbrown; 01-06-2013 at 10:03 PM.
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