galvanic/stray voltage corrosion

[Mark]

I'm getting mixed advice about stray voltage and galvanic corrosion. I plan to leave my H28.5 in the water this winter. I checked the two zincs on the shaft earlier this summer and both were in good shape. If my boat is not plugged into anything, is it subject to stray voltage. I worry because a couple of years ago when I pulled the boat, both zincs were gone. However, I had left it plugged in at the dock for several days at a time several times that summer. The marina keeps a couple of bubblers going in the slips near mine. Are these something to worry about?

 

[Pete]

Mark, strya voltage

Mark,let me start by saying that I'm not a expert on this subject but since no one else has attempted to answer you I will try. You will be isolated from the marina electical system when your boat is disconnected but will still be subject to stray voltage from other boats. This might be a short answer but it is the best from my limited understanding of stray voltage. Hope someone else will be able to add to this.What you need is to talk to a real good marine electician! Go Luck!

 

[Alex]

You mightr be safe if..

..1. You keep your boat unpluget from shore power most of the time. 2. Boats moored near you have their shaft zinc in good condition too.. 3...moored not near metal boats..if you do use shore power extensivly (more than 10-20 full days a year), you may install a "Galvanic Isolator" on shore power(ground) wire , made by Guest , Professional Mariner , and just very few few others .Look W.M., Defenders , etc.If your shaft zincs hold 10-12 months , that is still within minimal reasonable margins, although in average they hold about 2 years (depending also on their size and quality); less than that , you have a problem.

 

[Bob Howie]

Stray voltage isn't your only problem

Mark,Your zincs can/are being eaten off your boat by either (A) stray voltage from other boats, marina equipment, whatever, (B) a DC leak aboard your own boat, i.e., the battery and/or AC system is leaking juice to the points of least resistance, (C) electrolysis and (D) combinations of all of the above. As the other gentlemen suggested, a galvanic isolator -- good ones start at about $150 -- will help you inside your boat and a good idea is to have all your metals electrically bonded to a common sacrificial ground or isolater. This is critical work; somewhat simple if you understand it, not so simple if you don't and of absolute NO use to you if you don't get it right. Good idea would be to talk to a qualified shipyard about this.The other thing, basic electrolysis or the interaction of dissimilar metals that are in contact with one another in a conductive environment, in this case, of course, salt water. Your shaft is one metal, your prop another, the cutless bearing perhaps still a third or a different alloy. There is natural galvanic response -- good example, let a piece of tin foil come into contact with one of your tooth fillings -- between all dissimilar metals. Electricity follows the course of least resistance to a ground and that's how some props get eaten off the shaft! Electrolysis will cause a metal to deteriorate at the molecular level. If your zincs are getting eaten up -- and they probably need to be changed at least once a year -- then they are doing their job.You can also give them a hand by getting some zincs, put then on a length of line and drop them over the stern and bow when you are in port. You can get relatively inexpensive plate annodes and that will help you out and protect your boat.You may or may not know that your rudder and engine have zincs too. Make sure they are in good shape. Your rudder stock will deteriorate and you will eventually drop your rudder if you don't.Hope this helps a little. Your's is a common problem, but one easily and relatively inexpensive to fix compared to the repairs you might have to pay for if you don't invest in a little extra zinc.Best regards,Bob