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Old 20-10-2018, 21:12   #1
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Exclamation Stray current corroded saildrives

Looking for some assistance, my 2013 Lagoon 450 has sat at a marina in Langkawi since the end of Feb 18. It has a Coppercoat treatment to the underside and I have a diver clean it between haulouts. There was a gap between cleaning (for health reasons by guy who overlooks my boat) on April clean nothing noted by diver, when cleaned in late September, diver said some corrosion on saildrive, sounded like anode ring needed replacement, asked local shipyard boss to have a look and he reported that legs were gone, and two complete new saildrives required. ( I was in Australia trying to work out what extent of damage was by phone with language barrirers) The boat was towed to the shipyard and the ‘dissolved’ saildrives were replaced. The battery isolator has been identified as damaged, probably due to a lightning strike, several boats in the marina suffered damage a few months ago, the dehumidifier timer stopped working about the same time?? The aircon sea water pump also caught fire when started, there is no blockage in the feed lines??
The 200 hour SD50 saildrives are now replaced with new SD 60 saildrives, it was in the slings of the straddle carrier/ lift yesterday when we tested everything was working and no leaks around new installation before leaving the shipyard. We noticed the house batteries were discharging 20A +/- with all switches off. We inspected that pumps in both bilges and non were operating. I instructed shipyard to put boat back on hard to find stray current.
The legs removed were in such a bad way, long term industry persons have never seen anything like it.
The shipyard is waiting for a specialist electrician to come to try and find isssue
Has anyone got any ideas where to look?
The battery isolator is due to arrive soon to be replaced, boatyard does not believe this is the problem, just does not allow various charging sources to be directed, example, port engine will only charge port engine battery only, gen set will only charge house batteries etc
I am anxious to find the issue, time is running out for the planned holiday, and
I cannot drop boat back in the water until issue resolved ( I do not want to be replacing two more saildrives) and except for the shipyard there are no facilities to haul out 7.87m beam cats here, and cannot hardstand store long term as commercial shipyard does not have available room.
Any suggestions??
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Old 20-10-2018, 21:23   #2
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Re: Stray current corroded saildrives

You need a marine corrosion analyst to track down the issue.
What country is the boat in ?
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Old 20-10-2018, 21:30   #3
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Re: Stray current corroded saildrives

The boat is in Langkawi Island Malaysia
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Old 20-10-2018, 21:36   #4
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Re: Stray current corroded saildrives

Guess there aren't any Certified Marine Corrosion Analysts there.

Try this .... Tracking Down Stray Current in Boats
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Old 20-10-2018, 23:09   #5
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Re: Stray current corroded saildrives

Are the engines still live when the batteries are switched off?

I found a boat with a direct connection from the battery to the starter.

A lot of euro boats now come with a negative disconnect switch to help slow electrolysis from the saildrives.

The other option is some link to the coppercoat, are the areas round the drives spared copper antifouling?
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Old 21-10-2018, 00:45   #6
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Re: Stray current corroded saildrives

Assumptions:

All switches are off therefore no positive connections from battery switch onward

Bilge pumps bypass switches and are direct connected to battery through fuses

-----

That's what it sounds like from your description. If you have 20A out of the battery with 'all switches off' then it pretty much has to be the bilge pump wiring. Or some rogue wiring that doesn't go where you think/where it should.

Are the bilges dry? Are there bilge pumps in the engine room? I'd start looking for bad insulation/bad connector sitting in water on the bilge pump wiring. You might be able to confirm by opening the bilge pump fuse(s) and seeing if the discharge current drops.
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Old 21-10-2018, 01:53   #7
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Re: Stray current corroded saildrives

When you say, “all switches off” does that incude the master battery switches?

Do you have an engine battery (or two?) separate from the house battery? Is that off as well?

If you can not find it by turning off switches, the only thing left is to start disconnecting cables.

Of course with a 20 Amp(!!!) Leak you should be able to track it down with a clamp on amp meter.
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Old 21-10-2018, 09:37   #8
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Re: Stray current corroded saildrives

I had the identical problem. The saildrives is isolated from the gearbox ( to which the saildrive is attached ) and engine with a rubber gasket. I had new gear and throttle cables fitted. The cable ends were not isolated on the motor attachment ends so the a circuit was formed from the gearbox and saildrives , through to the controls and back to the engine. Testing with a multimeter eventually picked up the flow. My one saildrive was shocking, as was the prop. Quick fix but devastating consequences. Good luck.
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Old 21-10-2018, 10:46   #9
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Re: Stray current corroded saildrives

Quote:
Originally Posted by YPSILANTI View Post
I had the identical problem. The saildrives is isolated from the gearbox ( to which the saildrive is attached ) and engine with a rubber gasket.
Volvo saildrives are not bonded.
Yanmar saildrives are bonded.

I see significantly more corrosion on Volvo drives.
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Old 21-10-2018, 14:52   #10
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Re: Stray current corroded saildrives

If you are connected to shore power when not on the boat I understand there is also a risk of stray circulating currents working their way through the saildrives back to earth (happened to our boat as well, just prior to buying our vessel)? Ideally the earth leakage circuitbreakers on the shore power would pick this up and drop supply but not all locations have these. The previous owner had a marine electrician install an earth isolating (circuit breaking) device and some people install full isolating transformers (in Australia they are 240/240 volt but very heavy). Something else to explore perhaps by your marine sparky?
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Old 21-10-2018, 17:22   #11
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Re: Stray current corroded saildrives

They manufacture saildrives out of Aluminum . Than it goes in salt water , under the water. A power boat with outboard engines is also aluminum but it gets tilted out of the water at times. For a engine foot to be in Salt water all the time it should be made of STAINLESS steel !
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Old 21-10-2018, 18:11   #12
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Re: Stray current corroded saildrives

Tell that to all of the aluminum hulled boat owners here. Stainless eh? Won't rust or corrode at all right??
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Old 21-10-2018, 19:24   #13
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Re: Stray current corroded saildrives

There also is a device that you can install that measures stray current in the water to alert you to potential problems. I do think the severe corrosion is related to your boat and not the marina. It really sucks to have these costly issues. Especially with your holidays upon you. I would be one nervous
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Old 21-10-2018, 22:14   #14
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Re: Stray current corroded saildrives

I always think of threads and stories like this when the frequent sail drive vs shaft drive arguments start up. I'm not a fan, and this sort of mishap is one of the reasons for this posture.

Sympathy to the OP.

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Old 21-10-2018, 22:50   #15
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Re: Stray current corroded saildrives

this is what i would do if in such position:

likely cause was lightening strike.

When electric expert arrives, put boat back in water and let him find out current source(s). Fix one, and start again. There may be more than one issue.

Should not be that difficult with 20 A. Selectively turn off batteries, then cables etc until you got the one that makes difference.

Hope you sort out quick.
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