Zinc melt

Ralph Johnstone · Jun 21, 2013

For a Quickie .................

divernick said:
I own a 2008 Hunter 38, with only one zinc on the stainless prop shaft. But it disappears in a very short time period. Or I think it is too short. We cruise the caribbean year round. We don't spend alot of time in marinas. The zinc only last a couple of months. What could be My problem.

Thanks
Nick
S V Knot Yet

................... install three zincs and then start looking for an external problem which is causing the depletion of your zincs. Maybe even add an overboard zinc when you're tied up.

If you spend your time in various marinas, you may never find the problem. If you do find the problem (which will be probably an unmaintained stink pot) he'll likely tell you to get stuffed. He doesn't care about his boat and he certainly doesn't care about your boat.

Sailvayu · Jun 21, 2013

You should have your bonding system checked. Could be a number of causes, bad shore ground isolator, Inverter not properly wired and so on. Although most people like to blame other boats 9 times out of 10 the problem is on their own boat. blaming someone else is just avoiding doing the work of finding the problem. The fact that you are not near other boats a lot would indicate you have an issue onboard. Check your bonding system with a ohm meter and make sure all the connections are good. if you are using all chain rode try grounding that as well. If you run a inverter or generator a lot that could be a source as well. Try reading up on the subject as there is a ton of info out there. Or you could hire a pro to help just make sure you ask about their experience with this type of thing. Sorry but honestly this is not the type of thing that lends itself well to online trouble shooting, you will get lots of advice but a lot will be wrong as well as a lot being good. hard to filter if you have no experience. Good luck

fstbttms · Jun 21, 2013

Rapid zinc depletion is usually (but not always) caused by a problem aboard the boat in question. Could be as simple as a bare wire in a wet bilge. In any event, putting a second zinc on the shaft is cheap insurance.

Charles Erwin · Jun 21, 2013

Maybe there is no problem at all. We are a bit short on facts.

Your boat is moving through the water most of the time - and water flow over your anodes is a factor in wasting. Water temperature is a factor and seawater temperature in your case is relatively higher than temperatures at 45 north. You should expect more rapid wasting because temperature and possibly water flow are relatively high in your case.

Comments by others concerning bonding -- are not helpful to you unless the underwater metals in your boat are bonded. If they are bonded then are there separate zincs from the shaft zinc? Also how many zincs do you install and where? Is your shaft electrically isolated from the motor by a shaft saver or other flexible coupler? Do you have wasting rate different from other boats? Do you use zinc? Have you used aluminum anodes instead? Are the anodes you use mil spec?

As to whether some hypothetical "boat problem" exists you can find out in less than two minutes. Measure your hull potential with a simple multi meter - positive lead the your shaft and negative lead to a pencil zinc (soldered to the end of a 25 foot wire) dropped over the side.

Charles

fstbttms · Jun 21, 2013

Charles Erwin said:
Maybe there is no problem at all. We are a bit short on facts.

If the OP is burning through a shaft zinc every couple of months, there's a problem. There is no scenario involving a sailboat where that can be considered normal zinc usage.

Charles Erwin · Jun 21, 2013

Yes - and the OP now knows how to quickly find any such problem without having to crawl around in the nether-regions of the boat.

One hopes he tells us the hull potential on his boat because anything else is just guesswork on our part.

By the way -- what is your take on zinc wasting rates in tropical seawater cases and
do you think aluminum would be a better choice a tropical setting? Also do you see increased/decreased anode wasting on boats that are constantly in use?

Charles

fstbttms · Jun 21, 2013

Charles Erwin said:
By the way -- what is your take on zinc wasting rates in tropical seawater cases and do you think aluminum would be a better choice a tropical setting? Also do you see increased/decreased anode wasting on boats that are constantly in use?

All my zinc replacement experience is limited to California, so I am not qualified to comment in zinc wastage rates in other locales. I have installed too few aluminum anodes to come to any conclusion about their longevity. But in theory they should last longer than zinc. Regarding your last question; I have never found a corollary between zinc life (in this case, "velocity wastage") and boat usage. I just don't think most boats move fast enough or often enough for that to be a factor.