sail drives having electrolisis issues

[rancher44]

I have posted on this subject before but after doing the following I am still having problems

1 check all grounding systems
2change zinics regularly every 2-3 months
3put in a galvanic isolator
4 used a "fish" to help with grounding
5 now changed the Zinics to real zinic
I leave the air [dehumitifier]on when U am not there .Also leave the the ice box on.
I don't know what else to do . I had to replace the sail drives 2 months ago and now my diver said the paint on new sail drive had bubbles on the paint .

The only thing I can think of now is to disconnect shore power to boat and run an extention cord in to run a couple of fans in each hull and a dehumitifier . I am in Florida so have to humitify the boat to avoid mold
.
I am on the end of a dock with several other boats

Any suggestion would greatly be appreciated

[Ostinato]

I have been told to totally isolate the engine and sail drive from the rest of the boat to reduce stray current. (Forget bonding everything together) This may require a separate starting battery and maybe alternator among things. Sometimes momentary relay switches can be used to help accomplish the isolation.

I would also have a ground isolator for AC. I am assume you have checked the AC polarity.

You also might consider a zinc hung over the side the boat that is connected to the sail drive/engine to help minimize the need to change zincs.

Is anyone else on your end of the dock having problems?

Sail drive corrosion is a scary thing; let us know how you solve it

[Captain Bill]

A guy at our old Marina lost his sail drives to electrolysis a couple of months before we moved in. He filed a claim with his insurance company and they sent out an investigator that measured the current in the water and found that the electrical system on the dock was not properly grounded. The insurance company lawyers had a "talk" with the marina owners. Not only were the new drives paid for, but the marina put in a new grounding system that had a metal rod driven into the bottom at each slip. We kept our boat there for over 4 years and never had any problems with our drives and we got 1 year out of our prop zincs and 2 out of the drive zincs.

[cruisersfarm]

I had a set once that was being eaten away. Was able to fix it in a couple hours.

Bad wiring from a previous owner.

If you can get a short haul, measure the voltage difference between the two drives in the slings, then trace through the wiring, unhooking stuff that's suspect until you find out what's putting a voltage difference across those drives.

Pay close attention to and added wiring, vs the wiring that came with the boat...

[rancher44]

Thanks for all the input .
I was wondering if I just unhooked the starting batteries to the engines when I am not there if this would isolate the engines and sail drives?
I am on the boat for about 3 weeks and then off for a month. Then back on for another 3 weeks . During the time I am on the boat I am off sailing .
I do have solar panels, air ,gen set and full set of nav equip wick does include radar.

[UNCIVILIZED]

Kind of a wild (read half thought out) idea. But if you make up a set of Really long leads for your multimeter, then you can test all sorts of things. After, of course, testing the resistance & voltage drops in the new leads.
Such as checking for voltage differentials between; various batteries & the water in various spots around your boat. Ditto vs. a few spots on your engines, as well as your drives.

Pretty much checking, methodically, with intent, & in order of likelyhood of finding problems(s), everything that you can think of, that might be out of whack with your boat's electrical system. Ditto on what might be awry in the marina's electrical system (near your boat), within reason.

Also, of course, document all of this. In addition to time(s) of each measurement, what's switched on or off; on the boat, on your neighbor's boats (within 20-50m), on the dock, etc.
That, & ask the local live aboards, if they've noticed any changes in their zincs, & relavent systems in the last few months, to years, too.

Heck, maybe even put all of your recorded electrical data into a spread sheet. And even if it doesn't help you, giving a copy of it to an electrically savvy boat guy, might assist him in tracking down the problem, if you can't.

Were it me, aside from making an obvious list of things to check with the meter, I'd also research it via the internet, & in Nigel Calder's (& similar) works.

You might get lucky, & for the cost of some wire, & a notepad... find the likely culprit.

[boatpoker]

Hire an ABYC Certified Corrosion Analyst. This can be a difficult puzzle to sort out. Even the major mfg's of saildrives disagree. Volvo insists their drives not be bonded while Yanmar demands bonding as per ABYC Standards.

Do not hire anyone who uses the term "electrolysis". Use of this term show a complete lack of understanding of the issues of galvanic and/or stray current corrosion as "electrolysis" by definition is a chemical change in an electrolyte due to the passage of electrical current.