450: Stray current corroded saildrives

[Cadence]

With a 20A draw I would expect you have one large item running, which should be obvious? It would make me think that if this has been existing you are connect to shore power at the marina or your batteries would be stone cold dead. After reading numerous accounts of "electrolysis" , so I don't get corrected, I would spring for an isolation transformer. I feel sure that some parts of the world do not have reliable grounding on the electrical service at the dock. A transformer might be a one time investment rather than frequent sail drives.

[feebs]

Contact this guy. His is a specialist in stray currents.

Brian Gatt
m: 0416 644 066
e: brian@logixgroup.com.au

[David B]

Originally Posted by Sparky55

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??

Sorry to hear the problem. Some photos would be interesting for us all. hopefully the new drives were covered under insurance from the lightening strike?)
When it is all sorted, suggest you install a galvanic isolator so that any leakage from other boats cannot use your anodes (or saildrives …).

[Privilege]

They replaced both sail drives completely? Surely only the legs were corroded and they are usually straightforward to replace without removing the entire drive. I would have a real problem with this, especially seeing as they are not able to locate a 20amp leak.
It sounds like you have a number of issues causing a number of potential leaks. Even when you identify the 20amp leak you will need to monitor your drives to see if there are any further hidden leaks which are eating away at them. If I were you, I'd make sure that I had the type of anodes which can be replaced without removing the prop. It becomes a 10 minute job with scuba gear. Monitor your anodes. If they are only lasting a couple of months (or less) you still have a problem. Despite what has been suggested, the drive legs are not isolated from the rest of the drive or the engine. The rubber is just there to keep the water out. The anodes are the first to go. Your drive legs will only start to corrode once your anodes are gone.

[rom]

Originally Posted by Sparky55

We noticed the house batteries were discharging 20A +/- with all switches off.

It is not clear to me whether this happens when on the dry or in the water. Can you clarify ? With all switches off it should be very easy to find out what's eating 20amps, and I don't think this is related to your SD problem anyway.



If I wanted to self destruct my SD legs I would connect them to the negative side of the battery and would then connect the main ground copper plate (or some bronze thuhull) to the positive side. I can't think of any other way. This is extremely unlikely to happen.


The problem more likely comes from your marina and I suppose you insurance will want to find out. FWIW, I would never leave my boat connected to the dock long term, even with a isolation transformer. If I were to stay on the boat long term in a marina, I would buy an isolation transformer.


Good luck, please keep us posted, I would also be interested in pictures of the SD.

[Cadence]

Originally Posted by rom

It is not clear to me whether this happens when on the dry or in the water. Can you clarify ? With all switches off it should be very easy to find out what's eating 20amps, and I don't think this is related to your SD problem anyway.



If I wanted to self destruct my SD legs I would connect them to the negative side of the battery and would then connect the main ground copper plate (or some bronze thuhull) to the positive side. I can't think of any other way. This is extremely unlikely to happen.


The problem more likely comes from your marina and I suppose you insurance will want to find out. FWIW, I would never leave my boat connected to the dock long term, even with a isolation transformer. If I were to stay on the boat long term in a marina, I would buy an isolation transformer.


Good luck, please keep us posted, I would also be interested in pictures of the SD.

The bonding of the aluminum SD to a bronze through hull is an interesting thought. Since it sounds like his problem previously did not exist, it does not sound like it his problem but is definitely something for boaters with SD or an outdrive kept in the water to consider

I'm with you on the marina, in all likelihood, being the problem. A suggestion on an isolation transformer would be to get a buck boost one. That way lousy voltage supplies, at the dock, could be compensated for. If spending the money solve two possible problems.

[boatpoker]

While not impossible that the issue is related to the marina, it is extremely unlikely. DC just can't travel that far in salt water. The vast majority of stray current issues emanate from the vessel that is suffering from the condition. I say "vast" but I've never actually seen the issue caused by another boat and neither have have of the people who took the Marine Corrosion Analyst course with me.
An isolation transformer does not protect you from a DC leak on your own boat. DC stray current is the only type of current that could cause the damage described.

[Cadence]

The Isolation transformer precludes the need of bringing a ground aboard which may not be at the same potential as that provided by the salt water thus creating a minute DC difference in potential. I has nothing to do with AC.
Maybe someone that is a physicist can explain it. That minute current flow
24/7. Possibly the marina sticking in a grounding rod close to the water would solve it so they are not depending on that provided my the utility co. which could be miles away? Best case at the marina's service with an ground.i

[flyingfin]

You may want to install a MercCathode system to protect the lower unit. But first drop a zinc grouper overboard and monitor the stray currents in your harbour. It may be other vessels or docks creating the problem. And always install more zincs than you think are necessary.

[boatpoker]

You can quadruple the anodes if you like, it won't protect you from stray current.

If the marina has an electrical system they already have ground rods.

Cathodic protection is pretty much irrelevant with stray current corrosion.

[Cadence]

Originally Posted by boatpoker

You can quadruple the anodes if you like, it won't protect you from stray current.

If the marina has an electrical system they already have ground rods.

Cathodic protection is pretty much irrelevant with stray current corrosion.

But how far from the water is or are their ground rods? The stray current corrosion is a minute amount of current. Be real nice if someone had the answer.
Maybe the boat next door has their battery anode connected to their block. I don't buy an adjacent boat is causing it.

[boatpoker]

Originally Posted by Cadence

Maybe the boat next door has their battery anode connected to their block.

Dear OP. The statement above is a perfect example of why you should not take advice from this forum.

[skipperpete]

My condolences to the OP re the loss of the sail drives to what appears to be electrolysis, it seems to be fairly common on boats in langkawi with no common thread linking the events. A recent SD 50 saildrive on a grp monohull was destroyed by very specific and severe corrosion that ate away the lower shaft bearing carrier but not the leg itself. Seawater had entered the saildrive so it was replaced with a complete new SD60.
Prior to this, a low hours 4JH series Yanmar was substantially destroyed by what can only have been electrolytic corrosion and required a new engine, propeller and shaft. The corrosion attacked along the raw water intake and the first casualty was the oil cooler and then the heat exchanger which leaked onto the starter motor at the rear and the circulating pump at the front, destroying them both due to simple saltwater corrosion. .
Hope the photos are attached

[boatpoker]

Originally Posted by skipperpete

My condolences to the OP re the loss of the sail drives to what appears to be electrolysis, it seems to be fairly common on boats in langkawi with no common thread linking the events. A recent SD 50 saildrive on a grp monohull was destroyed by very specific and severe corrosion that ate away the lower shaft bearing carrier but not the leg itself. Seawater had entered the saildrive so it was replaced with a complete new SD60.
Prior to this, a low hours 4JH series Yanmar was substantially destroyed by what can only have been electrolytic corrosion and required a new engine, propeller and shaft. The corrosion attacked along the raw water intake and the first casualty was the oil cooler and then the heat exchanger which leaked onto the starter motor at the rear and the circulating pump at the front, destroying them both due to simple saltwater corrosion. Attachment 179580Attachment 179581.
Hope the photos are attached

What is the difference between electrolytic corrosion, electrolysis, galvanic corrosion, stray current corrosion and simple salt water corrosion ?

[skipperpete]

Good question and I don't fully understand the precise definition but I would describe ordinary corrosion as occurring where saltwater simply drips onto a metal surface and eats into that surface but electrolytic corrosion in all its forms requires an external electrical input through , in these instances a salt water conductor. Bi metallic corrosion between metals is a whole other mystery but might also be described as electrolytic. In both the incidents , no reason was ever discovered for the damage so would appreciate any enlightening views on this. The propeller and shaft attached to the 4JH were both destroyed, even the nut and most of the key. Both boats were in marinas.