Hanging zinc block

A recent poster mentioned hanging a zinc block off the side of his boat for added electrolysis protection. I have seen this on some of the boats at the marina and have often wondered if there is any real benefit by doing this, and if there is some benefit, how can you be sure without having a diver come to check your zincs. I haul my boat every 3 years and have a diver change my zincs twice each year. On my boat I have 2 shaft zincs, 4 plate zincs (2 on the rudder and 2 on the skeg) and an acorn zinc on my bow thruster. The acorn zinc is the only one that really needs to be changed bi annually, but I also change the shaft zincs twice a year and the plate zincs annually. So Im wondering if any of you guys do this and is there any noticeable change in the condition of the mechanically fastened zincs. I recently delt with some electrolysis issues on my boat and the serviceman tested my protection and determined that I was slightly over zinced so Im not concerned about extra protection, just curious if it really helps or not. I was talking to one of the guys at the marina who does this and he swears by it, says he never needs to change his zincs. Im skeptical. What do you guys think.


-- Edited by DCBD on Thursday 17th of February 2011 11:58:03 PM

Get a hold of a marine electrician who understands zincs and has the ability to test your boat using a silver/silver-chloride (Ag/AgCl) reference electrode. I have heard that you can over-zinc a boat.

DCBD wrote:A recent poster mentioned hanging a zinc block off the side of his boat for added electrolysis protection. I have seen this on some of the boats at the marina and have often wondered if there is any real benefit by doing this, and if there is some benefit, how can you be sure without having a diver come to check your zincs.

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We, like many boaters in our marina, hang a zinc on a heavy wire over the side of the boat with the other end fastened to the boat's bonding system.* In our case the wire is clamped to one of the rudder posts.

The reason we do it is that the head of Bellingham Bay often has a layer of fresh water on top of it.* A large river dumps into the bay, the Nooksak, and on either side of the marina there are two fairly high-volume streams, Squalicum Creek and the Whatcom River.* Depending on the rainfall and the snowmelt in the mountains, the surface water in the marina can be nearly fresh. Dip your hand in it and taste, no salt taste at all.

The transom zincs on a GB are only* a few inches below the water line because of the very low draft of the boat at the transom.* And the shaft zincs, which are deeper, are not very large.* So we hang a zinc-- usually a worn-out transom zinc--- on a wire down about five or six feet so that it is in "good" salt water regardless of the salinity of the water near the surface.* This ensures that there is more than just the little shaft zincs protecting the boat.

Squalicum Marina is a fairly "hot" harbor if you believe in such things. As such, I hear that zincs on most boats are ready to be changed (or are already gone in the case of small shaft zincs) about every six months or so.* I can change the transom zincs myself but we have a diver check the shaft zincs and the rest of the bottom of the boat every six months.

I know that a wood boat can be over-zinced with consequences to the wood around bronze through hulls and such.* I have not heard that over-zincing can be a problem with grp boats.* What are the symptoms of over-zincing a grp boat?

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I get a kick out of* folks*hang one over the side...with a rope!

Keith wrote:

I get a kick out of* folks*hang one over the side...with a rope!

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Well, someone got really angry with me once when I questioned his recommendation of attaching zinc anodes to a wooden dock.

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I saw one once that was hanging in the water with a battery clamp attached to an aluminum window frame, made me wonder!!

The divers at my marina often leave the old zincs behind the boats they've been working on. I've wondered if it would be possible and practical to melt them down into a block and use that.

rwidman wrote:

The divers at my marina often leave the old zincs behind the boats they've been working on. I've wondered if it would be possible and practical to melt them down into a block and use that.

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We have bought new "recycled" zincs at Fisheries in Seattle before.* They lasted as long as any others.

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One of my boating friends has made a few in his basement using a plumbers pot and old zincs he's been scrounging for a few years.
I think he used an old cast iron skillet as a protoype mold.
If I can find out how they do I'll advise, but it won't be until the end of the 2011 season at the earliest.

The zinc*grouper anode with clamp and wire are about 50 bucks.* I have two, one connected to the bow thruster, and another from the engine room.* They do prolong the main zincs.**I mainly hung them as its*about 50 ft from the bowthrust to the main stern zincs,*so it a*direct shorter path.* **

Dave, are you in salt or fresh water?
it almost sounds like your zincs are deteriorating too slowly..
more zincs would not help you much, it sounds like possible you should have the bonding checked out to make sure it is properly connected and bonded.

Per wrote:

Dave, are you in salt or fresh water?
it almost sounds like your zincs are deteriorating too slowly..
more zincs would not help you much, it sounds like possible you should have the bonding checked out to make sure it is properly connected and bonded.

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Yes Per I'm in salt water. This is my second boat at the same marina and in both cases the zincs have lasted about the same time (which I think is normal for here). I have actually had a marine technician check my bonding and test the water around my boat while he was here on another issue and he determined that I was slightly over zinced with 2 month old zincs, so I think everything is OK.

I was only curious about other boats I've seen with questionable applications of the hanging zinc, which couldn't possibly be doing anything to enhance their bonding. I've always been of the opinion that mechanically fastened zincs, located properly*work best and was wondering if there was any real benefit to hanging a zinc off the boat. It seems that the people who do it still have their zincs changed*on the same schedule that I do so it seems like it's more of a comfort factor in most cases.

How is your solar panel installation coming? Be sure to post pictures.

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DCBD wrote:I was only curious about other boats I've seen with questionable applications of the hanging zinc, which couldn't possibly be doing anything to enhance their bonding. I've always been of the opinion that mechanically fastened zincs, located properly*work best and was wondering if there was any real benefit to hanging a zinc off the boat.
I have a stern zinc that's not directly connected to any underwater metal, just to the bonding system.* That's pretty much the same as a hanging zinc as long as it's connected electrically to the bonding system.

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How is your solar panel installation coming? Be sure to post pictures.

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its forthcoming, still cant quite figure out where to mount the panel.

http://www.trawlerforum.com/forum.spark?aBID=115492&topicID=40951707&p=3&page=4

DCBD

A good book on the subject is "The Boatowners Guide To Corrosion" by Everett Collier. I note you are in the Victoria area, it's available from the local library system.

Doug wrote:

DCBD

A good book on the subject is "The Boatowners Guide To Corrosion" by Everett Collier. I note you are in the Victoria area, it's available from the local library system.

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Hi Doug,

I have a copy of that book, and even managed to read right through it, probably the driest book I've ever read. Anyway, I was never concerned about my own bonding, just curious how many people use hanging blocks and if it actually delayed the twice yearly diver visit*to a once yealy experience. It seems that some do use it, but still change the zincs twice yearly. So no point for me I think.

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