Overzinced?

[Charles Erwin]

Not possible here -- the boat is anchored thus no AC.

By the way - did your dockmaster/diver explain how stray 110 AC can cause accelerated zinc loss?

 

[Malcolm/Trilogy]

I'm Zinc-ing of you

Is it possible to "over zinc?" Recently added zinc since old ones were wearing (see photo). Pulled yesterday to work on keel rust and painter in the yard said I was "overzinced."

Steve - not sure I can answer your actual question but may I raise another point. I live in China, and I shipped my Hunter 42 to Hong Kong in 1996 and have lived and sailed happily to and from here for 17 years. When my boat first arrived I would sail when I could and motor when I couldn't (there is not always sufficient wind to get to the restaurant on the outlying island) but the (one) zinc on my prop shaft hardly deminished. As she got older I noticed a significant increase in the erosion of the zinc and so I placed a second one on the prop shaft and when I had time I replaced the earth wire around my bilge to reduce the amount of wear. This seemed to help for a while but more recently I have been placing three zincs on the prop shaft and they have been eaten away in very quick order. So I am thinking that when I have her out of the water in February I will replace the earth wires and move back to two zincs and see what happens - anything significant I will write to you.
Malcolm B

 

[Calif. Ted]

The AC line was in the water, water around the dock had a charge or potential difference from ground, they changed out the wiring and zinc usage returned to normal. good enough for me, that's all i was looking for.

 

[alexco38]

Google galvanic isolator. You can make one for $20 parts. Pretty much all new boats comes with one. Hunter even use isolation transformer.

Zinc on my prop shaft last 4 years+
My neighbor has to change every year.

 

[AyeSail]

I'm not certain how to use all the suggestions in this thread to address my situation, so I'll ask the following, after teeing it up.

I have a Beneteau 343 (2006). It was commissioned with a small cone-shaped zinc that attaches to the aft end of the stock 3-blade prop. It appears a larger zinc can not be accommodated aft of the prop, and there is no room to attach another zinc, of any size anywhere since very little shaft is exposed.

I'm located in a small marina about half way up the Chesapeake Bay, just a little north of Annapolis and the Chesapeake Bay Bridge. So, it's a mixture of both salt and fresh water. The zinc wears to almost nothing after about four months, so I dive and replace it myself, almost every three months while in the water, and I haul every other year for the off-season. All fitting (overboard fitting from sinks, shower, head, etc.) are in quite good shape, both outboard and inboard, each time I haul.

I broached this fast deteriorating zinc issue with the Beneteau dealer/manufacturer, and all I got was to make certain I change the zinc regularly, before it begins to loosen up from good contact with the tail end of the prop. Seems to me the zinc, albeit small, is wearing to quickly.

It was recommended to me a couple years ago to hang a zinc guppy over the side when in my slip, and attach that zinc guppy via large gauge wire to the engine block to ensure a strong ground. The zinc guppy, purchased from West Marine, so it's standard (about 2 pounds weight), I suppose, doesn't seem to help very much. So, would this zinc guppy be considered "over-zinced?"

I received another suggestion to use aluminum as opposed to zinc, due to the mixture of fresh and salt water, but I discounted that suggestion, what with the dealer/manufacturer commissioning the boat with zinc.

I'm interested in any constructive thoughts on this dilemma, including responses from other B343 owners who may or may not be experiencing the same scenario.

Thanks all,

 

[Charles Erwin]

With or without the zinc "guppy" you do not have too much zinc. The guppy system is essentially the same as if you added more zinc to the shaft/propeller assembly. Obviously the guppy zinc is not in play when you are using the boat. Since the rate of zinc loss of the shaft zinc is the same - guppy or not - and if the guppy is in place most of the time you need facts.

Is this rate of zinc use something new or has it always been so?

Measure the hull potential of the boat. If you have shore power measure also with cord both fully disconnected and connected.

Charles

 

[AyeSail]

Thanks, Charles,

I'll print out this thread, and once the boat is back in the water in April, I'll attempt to do some of the measurements herein.

 

[fstbttms]

I'm interested in any constructive thoughts on this dilemma, including responses from other B343 owners who may or may not be experiencing the same scenario.

Consider adding a limited clearance collar zinc to the shaft. These are designed for use on Beneteaus with very little exposed prop shaft. You need the 25mm size:

http://www.boatzincs.com/beneteau-donut-collar-specs.html

 

[Patrick S/V Shangra-La]

Google galvanic isolator. You can make one for $20 parts. Pretty much all new boats comes with one. Hunter even use isolation transformer.

Zinc on my prop shaft last 4 years+
My neighbor has to change every year.

DITTO!!

My zinc (single) lasts about 3 years on my shaft, most others in the marina about 8 months.

 

[mauruuru]

tOO MUCH zINC MAYBE BUT NOT BECAUSE OF THE GALVANIC CELL

In theory, yes.

Consider what you are doing by using anodes - you are creating a battery with the anode acting as the termination through which the current flows. You can create a battery too large by having excess anode material.

Sure the zinc sets up a galvanic cell. But the voltage is a function of the material it will not go up as more zincs are added. The current flow set up by that cell is a function of the galvanic voltage and the circuit impedence. Placing more zincs on the shaft will look like batteries in parallel but each cell will have the same voltage and drive the same (very small) impedence-limited circulating current so adding more zincs is not an electrolysis promoter. Remember why they are there, they are the sacrificial anode when external currents are flowing (not due to the zinc/stainless/seawater interface). However, there is a practical limit in terms of shaft vibration/deflection and loss of energy due to angular momentum-again small. I routinely put two on my prop shaft just in case one falls off before the next haul out. But, if you are going to the trouble, don't leave on a half eroded, film encrusted zinc-replace it with a new one at the same time...they are cheap insurance.

 

[AyeSail]

Consider adding a limited clearance collar zinc to the shaft. These are designed for use on Beneteaus with very little exposed prop shaft. You need the 25mm size:

http://www.boatzincs.com/beneteau-donut-collar-specs.html

Thanks, fstbttms, I believe this is exactly what I'm looking for. I have a Shaft Shark on my shaft, just forward of the prop ... trustfully there will be enough room to add the "narrower" donut to the shaft. If not, I'll consider removing the Shaft Shark. That would be unfortunate, as I've been saved on a couple occaisions whereas lines from crab pots and such found their way into channels and caught onto my shaft and or prop and were successfully disengaged by the Shaft Shark. In any event, I will go forward with the extra zinc, the opportunity cost notwithstanding. Again, thanks.

 

[AyeSail]

Thanks, fstbttms, I believe this is exactly what I'm looking for. I have a Shaft Shark on my shaft, just forward of the prop ... trustfully there will be enough room to add the "narrower" donut to the shaft. If not, I'll consider removing the Shaft Shark. That would be unfortunate, as I've been saved on a couple occaisions whereas lines from crab pots and such found their way into channels and caught onto my shaft and or prop and were successfully disengaged by the Shaft Shark. In any event, I will go forward with the extra zinc, the opportunity cost notwithstanding. Again, thanks.

By the way, does anyone know the diameter of the shaft on the Beneteau 343? I checked the owners manual, and could not find that data. The choices for the Donut Collar zincs are: 25mm, 30mm, and 35mm.

Thanks.

 

[AyeSail]

Just spoke with the dealer ... it's 25mm. Thanks.

 

[fstbttms]

Just spoke with the dealer ... it's 25mm.

...as I mentioned in my previous post. Two days ago.

BTW- the zinc is appox. 5/8" thick.

 

[AyeSail]

...as I mentioned in my previous post. Two days ago.

BTW- the zinc is appox. 5/8" thick.

Please accept my sincere apology. Unfortunately, I merely scanned your post, and went directly to the photo, and clicked on the link for the zinc. A bad habit, for sure.

You certainly deserve to full credit for a comprehensive post that provided all I needed. Thanks very much.

Since my boat is on the hard, I'll check the clearance to see if I have to reposition the Shaft Shark, or remove it all together. I've already ordered two of the zinc you recommended.