Are multiple zinks better than single?

[Island Girl 34]

I have an 83 H34 that I have owned for about 6 months. I had the boat pulled and sounded during a pre purchase survey. The zinc on the shaft was mostly gone so it was replaced then. I plan to pull the boat to do a botom job next month and will be curious to know how this zink has lasted.

Now to the question. Is there any value in installing multiple (like 2, 3, or 4) zinks on the shaft when I pull the boat? Will that make any difference at all in the overall zink life expectacny? My thougts are that if there is a certain amount of galvonic conduction eating away at the zink, would not having more zink on the shaft spread the loss and extend the life of it?

I'm sure many here have had this thought and have tried it but I have not been able to find anything searching this forum on the issue. Would love to know the answer...

Thanks,

Ken

 

[Allan12210]

Putting the extra zincs on in my case means I have to change the zincs less often. Basically spend twice as much for materials to last twice as long. The savings is only one trip below the surface.

I put two zincs on the prop shaft of my H34. I also drilled a hole through the strut and put a 3" diameter pancake zinc there. It is not bonded to anything on the inside, but the strut had turned pinkish (zinc depletion) so I installed it. Don't know if it does any good or not, but I have it changed about every six months along with the two on the prop shaft.

Allan

 

[Don S/V ILLusion]

Ken
Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they are not needed or adding too many will result in the zincs eroding away since they create the battery situation where none or fewer may have existed.Essentially, by adding too many zincs, you may create a worse scenario.


Having said that, two other points:
1. I use two on my shaft for the simple reason that one can fail and fall off for reasons other than electrolysis - the second is basically a back-up, and
2. if your zinc(s) are lasting less than 6 months, that is indicative of a galvanic problem. Rather than treat the symptom, I'd suggest you identify and fix the underlying problem.


Also recognize that the range of protection a zinc can supply to other metals bonded to it is limited by the conductivity of the water. In salt water you get coverage for a radius of about 4 to 6 feet. A zinc on the stern of a 14 ft boat where everything is bonded is only protecting half the boat. This range gets even less in fresh water and may reduce to only inches. Often magnesium is substituted for zinc in fresh water to provide an even higher voltage to push through the fresh water. I don't know where "Little Creek" is but if that is fresh water, note the above.

 

[Island Girl 34]

Allan,

Thanks for the info.

Don,

Thanks to you as well. Little Creek, Va is just around the corner from the Naval Station, Norfolk, on the lower section of the Chesapeake Bay - definately salt water.

Not sure how long my zink is lasting. Will be pulling the boat for the first time for me next month. From what the two of you say, it makes good sense to use two zinks on the prop shaft. That will be the way I go and see how that lasts.

Thanks again!

Ken

 

[Warren Milberg]

I had been putting one zinc on the bronze shaft of my h28.5 and found that it was about 65% shot at the end of one season on the mid-Chesapeake, which is probably a bit less salty water than Little Creek. In my case, I am very near a transient dock that often gets some big boats passing through. Many hook up multiple 50-amp shore power cords and leave them connected as long as they are there. I have suspected the shore power stands at my marina may be not be thoroughly or completely grounded and may be the culprit allowing stray current into the surrounding waters. In any event, electrolysis may also come from the DC side of your own boat and is very difficult to check. I've added a second zinc on my shaft for a few years now and have found they are doing the job well in protecting my underwater metals.

I also asked boating expert Don Casey to comment on this and here is his reply:

"Current flowing to your boat from an outside source would indeed eat away your anodes, but this requires a complete circuit, meaning your boat would need to be plugged in to the shore circuit. A more likely scenario is that your shaft is connected to the ground side of your electrical system through the ground lug on your engine, and somewhere in your electrical system is a small ground-fault that is energizing the shaft. This assumes that you feel confident that the anodes are not sacrificing themselves simply due to dissimilar metals in the water, given that your shaft is bronze rather than a steel alloy. There is also the issue of what alloy these anodes are compared to the one you had installed last year. Not all anodes are the same on the galvanic scale, which will affect how long they last.


This seems like a case where you should check all of your onboard circuits for leaking current. You can find instructions for doing that in Sailboat Electrics Simplified. If this effort does not reveal a current leak, then the recommended treatment is what doctors now call watchful waiting. Put on fresh zincs and keep an eye on them"

 

[Dan Johnson]

The first year...

I owned my H34 it was on an old wooden dock with very questionable electrical wiring due to age and hurricane damages. The single shaft zinc was fairly well eaten after that season and had to be replaced.

The past two years it has been on an all new floating dock system that replaced the old wooden docks. It has all new wiring, properly installed and checked, with modern dock termination points. The shore power cord is disconnected from the power socket at the dock prior to each departure from the boat, even though the breaker is turned off too. Most boats around me do the same thing.

The shaft zinc was replaced after each season when the boat was put on the hard. The amount of deterioration was significantly less after each season and not replacing it was tempting. A new zinc will go on shortly for piece of mind as one can't predict what will be encountered when visiting other marinas. Stray current most certainly had been the source of the deterioration in the first year as subsequent years have not had nearly as much zinc loss.