Zincs

[Mary L]

I have a 1981, 32 ft. Island Gypsy. I am trying to find some information regarding zincs for corrosion control, particularly the ones on the back of the boat. Is there one on the propeller shaft? Is there one on the rudder? Is there one zinc in the middle of the back of the boat or two smaller ones, one on each side?

Thanks.
Jim

 

[boatpoker]

Jim : there is no set pattern for anode size or placement. It depends on the electrical condition of the boat and the marina you keep her in. You can either stick anodes where ever you like and monitor for corrosion or you can hire someone like myself to conduct a corrosion survey and get it right the first time. I suggest you hire someone who is, like myself an ABYC Certified corrosion Analyst. ..... although I have no interest in coming to Skagway

 

[BruceK]

Jim, My 36 has one large zinc on the transom, one on each prop shaft, none on the rudders.

 

[Old deckhand]

Skagway, Alaska.....Canada?
I do not understand.

 

[Capt Kangeroo]

We bought it back, 2 chests of coloured beads and 500 beaver pelts.

 

[fstbttms]

I have a 1981, 32 ft. Island Gypsy. I am trying to find some information regarding zincs for corrosion control, particularly the ones on the back of the boat. Is there one on the propeller shaft? Is there one on the rudder? Is there one zinc in the middle of the back of the boat or two smaller ones, one on each side?

The one Island Gypsy 32 I count amongst my customers carries only one anode- a 6"X12" slotted plate on the transom. Commonly called a "Diver's Dream":

 

[DavidM]

As boatpoker noted, there is no firm requirement for zincs. Mine has a transom zinc, one on the prop shaft, one each on the trim tabs and one on the rudder. I also hang a guppy off the side. That may be over zinced but it keeps the wastage low.


At the minimum I would put one on the transom and two on the prop shaft if you have no others. Make sure that the transom zinc is connected to the boat's bonding system.


David

 

[knotheadcharters]

DJMARCHAND, What do you connect the Guppy to? I am going thru zincs a little faster since I moved slips and those damn diver plates are 110 a piece!

 

[Larry M]

DJMARCHAND, What do you connect the Guppy to? I am going thru zincs a little faster since I moved slips and those damn diver plates are 110 a piece!

I see you're in JAX. Last year I had a corrosion analysis done by Eric Weatherly in JAX. I worked with him and it took one hour ($65). He's a local and ABYC Corrosion Certified. It's an easy way to find out if you have a problem and if you do, where it is and what to do about it.

 

[Marin]

On the advice of our marine electric shop we, too, hang a zinc over the side about eight feet down on a heavy cable. The other end of the cable is connected to the boat's bonding system. In our case, I clamped it to one of the bronze rudder bars in the lazarrette. Obvoiusly the hanging zinc needs to be connected to the bonding system. Just hanging it down there on its own does nothing.

We think the "purpose made" guppy zincs are a bit of a rip off. We use transom (license plate) zincs we get from the dive shop we use. They are about half gone because they are zincs they remove from boats on a regular schedule, but they are free. On occasion we have purchased a new transom zinc for the hanging zinc.

 

[DavidM]

The hang off the side zinc used to be a fish shape piece of zinc with a bonding wire connected. But the last one I bought at boatzincs is a plain cylinder which should work just as well. It is now $50 and has a stainless alligator clamp to avoid corrosion of the clamp which used to occur with their old clamp.


I connect the bonding wire to the rudder stock which in turn is connected to the bonding system of the boat.


Contrary to Marin's practice I have read and it makes sense that a suspended zinc only has an effective protection radius of several feet. So I drop mine down near the rudder where it is a foot from the rudder and maybe 3' from the prop.


My prop shaft zincs last about a year and the ones on the transom and the trim tabs last two years.


A corrosion survey for $65 would be a good investment.


David

 

[Marin]

We use ours for a different reason than most people. Our harbor has a large stream dumping into the bay right next to the west harbor entrance and a river (Nooksak) entering the bay a couple of miles away. The circulation of water in the bay means the harbor has a layer of fresh or nearly fresh water on the surface pretty much year round. On boats like ours, the transom zincs are only a few inches under the surface. This renders them much less effective in our harbor than if the surface layer of water was more conductive. Which means the zincs that are doing the hard work are the shaft zincs that are below the layer of fresher water (as are the through hulls, props, rudders, etc.). The shaft zincs are much smaller and disappear much faster than the license plate zincs.

The solution is to hang a zinc down into the much more conductive salt water under the layer of fresh or brackish water. Thus the eight foot cable.

Many of the boats in our harbor do this, and it extends the life of deeper water zincs like shaft zincs by quite a bit. If we were in a harbor with "full strength" salt water from the surface down we wouldn't use a hanging zinc at all.

Obviously we need to remember to pull the hanging zinc up before we move the boat, so my wife made a big red fabric stop sign that says "Zinc" on it that we hang on the shift levers when the zinc is down and remove when the zinc is up.

A nice benefit of the hanging zinc is that since we can simply pull it up, we have an ongoing check of how conditions are in the harbor. If the hanging zinc starts going away at a faster rate than normal then we know there might be somehting going on, either with our boat, a neighboring boat, or the harbor's power system. So far in 17 years we've not had any abnormal dissolve rate on the hanging zinc or the boat's zincs which we have checked by a dive shop every six months.

The hanging zinc goes away at a faster rate than the two license plate zincs because the hanging zinc is in a much more conductive environment than the zincs on the transom. Our harbor is rather "hot" and the standard Martyr Diver's Dream license plate zinc needs to be replaced every six months or so. From what I've been told by other boaters and the dive shop we use, this is about average for the boats in our basin. I don't know what the conditions are in the other basin. I can replace the license plate zincs myself but we obvously need a diver for the shaft zincs (we have two on each shaft).

 

[psneeld]

Wow...I'm not certified but have been doing my own and other zinc surveys and before anyone believes a post and doesn't understand the basics of Galvanic corrosion....learn more!!!!


below is the basic concept...but ultimately more complicated per boat...


https://en.wikipedia.org/wiki/Galvanic_corrosion

Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact, in the presence of an electrolyte. This same galvanic reaction is exploited in primary batteries to generate an electrical voltage.


The metals technically have to be in the same electrolyte and the resistance has to be less than to block the process of the sacrificing of the zinc.


And I just use fairy dust and it works for me...for all the naysayers out there.


Seriously...not familiar with it...get a pro at it .....not just "some recommendation" from a generalist.


Or if it's working on the boat next to you...well heck..give'it a try...just don't guess wrong!!!