Hot Marinas

[goldstar]

After reading Mike Holt's November 17th newsletter about "hot marinas" I passed the newsletter along to my friends at one of my supply houses. Today we got into a conversation regarding this very subject and one fellow (who happens to be a boat owner) mentioned that he has a piece of "sacrificial metal" (usually zinc) attached to his boat so that it will corrode before othet metal parts on the boat will. He mentioned that he does this specifically because other boat owners around him in the marina do not use proper attachment cords for their boats and the cords sometimes hang down in the water. In addition their boats are not properly grounded.

If anyone can shed some light on the practice of using "sacrificial metal" for boat hulls I would be interested in hearing about it (i.e the thought process behind it, is it reliable, etc.).

Thanks,

Phil

 

[tom baker]

Re: Hot Marinas

"zincs" have been used for years to protect boats from corrosion. I have a water reservoir with suspended zincs, it has a cathodic protection rectifer to impress a DC voltage. There is much information available on this topic, I imagine a google on cathodic protection systems will get you started.

 

[Guest]

Re: Hot Marinas

I call them sacrificial anodes. I know brass boat propellers have them to protect the brass from the stainsless steel propeller shafts. The slang term is "zincs". Here's an interesting quote about zincs:

Electrical contact is essential:
There is an unfortunate misconception that a sacrificial anode can be mounted anywhere, even hung over the side on a string, and it will still perform its appointed duty. That is dead wrong!

For a zinc anode to provide any protection, it must be in electrical contact with the metal being protected. The conductivity of the water is not adequate. We need low-resistance, metal-to-metal contact-either by mounting the zinc directly to the metal being protected or by con- necting the two with a wire. A hanging anode can provide protection if it is connected by a wire to the metal being protected.

Where the zinc is mounted directly to the protected metal-bolted to the side of a metal rudder, for example-it is essential to make sure the surface under the zinc is bare and bright before the anode is installed. This is to ensure good electrical contact.

More on boat zincs

 

[goldstar]

Re: Hot Marinas

Tom & Wayne,

Thanks for your replies. This fellow at the supply house made it sound like the reason sacrificial zincs were used is because neighboring boats, electrically connected to dock side power stations, were emitting some type of electrical energy causing the metal on other boats (not producing electrical energy) to corrode. However, from what I read in the link that Wayne provided, galvanic corrosion occurs when two different metals are either physically OR electrically connected and submersed in seawater. It mentions nothing about being a result of the connections to dock side power stations.

Anyway, my whole reason for starting this thread was that I know that divers are often employed to dive down under large boats in a marina to perform various repairs to props or other areas of the boats. If electrical energy is being produced at dock sides (as in the case of the young girl getting an electrical shock) these divers are at great risk of electrocution. I'm wondering how far beyond the immediate area of the boat in the marina this type of energy can extend. Also, could the electrocution of those people described in Mike's newsletter have been prevented with simple GFI protection or is it more a more involved electrical design flaw ?