Do more zincs last longer?

sailcapt340 · Aug 11, 2020

You can contact Shoreline Diving Services - Capt. Richard Marquardt - Narragansett, RI
I've used his services in the past and highly recommend Capt. Richard. Honest as the day is long.
I also have sent you a PM with further info.

Don S/V ILLusion · Aug 11, 2020

ontherocks83 said:
Would having 2 zincs instead of one on the prop shaft slow how quickly they dissolve?

Is a zinc lasting 2 months average/normal?

Does anyone in the Narragansett bay area know of divers that could replace the zinc? (I'm new to the area and have not learned all the local resources yet)

Adding more zince can exacerbate the problem because you are effectively creating a battery by adding more anode material. Stated differently, adding more zinc is putting a bandaid on the infection. A zinc should last longer than a couple of months - sometimes a whole season. I'd find the problem before it destroys your prop.

Michael Davis · Aug 11, 2020

Our marina has no electricity on the docks. Zincs last a couple of years.

Ralph Johnstone · Aug 11, 2020

The mass of zincs on the shaft will increase the life expectancy. The surface area will increase the electrical potential to the max. theoretical.

Rich Stidger · Aug 11, 2020

My boat lives on a mooring during the boating season. Zincs last 1-2 years. I have replaced a zinc just because I felt guilty to leave it.
My mooring location is Prime Marina in East Greenwich. I have used a bottom cleaner with excellent results. I am certain he could replace your zinc. His contact info is:
Todd Patenaude
Diver at East Greenwich
155 Howland Road
East Greenwich, RI 02818
Bus: (401) 487-9198
Bottom Cleaning $120 after 8 weeks in the water - 7/31/19

Regarding adding more zincs- It is possible to "over-zinc". I think you really need to make electrical measurements using a Silver/Silver Chloride Half Cell to be sure you have the right amount of zinc to protect your particular boat.

Ralph Johnstone · Aug 11, 2020

Don S/V ILLusion said:
Adding more zince can exacerbate the problem because you are effectively creating a battery by adding more anode material.

Not disagreeing that the increased surface are will increase the potential, but how does it make the problem worse ?

I remember years ago being moored in a marina which doubled as a boat graveyard and in order to increase the short life expectancy of the two shaft zincs, I used to hang a 12" X12" zinc plate over the side and connect it to the shaft inside. Worked well 'til I got out of there.

Rich Stidger · Aug 11, 2020

OK, so I did a little bit of research to clear my recollection that it is possible to have too much zinc. And like many questions you can find conflicting answers. One answer is that it is not possible to over-zinc a fiberglass boat but it is very possible to over-zinc a wooden or metal boat.
Another answer is that too much zinc will affect the protection of copper-loaded bottom paints. This may be evidenced by a discolored ring around thru-hulls. This was the damage from over-zinc-ing that I remembered.
So read for yourself and pick the answer you want to believe:

Can You Have Too Many Zincs? - Practical Sailor

Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.

www.practical-sailor.com

Boat Corrosion 101 | Christian & Co.

Corrosion of metal components below the waterline will be a problem all boaters will eventually encounter and inevitably discuss with their boating neighbors.

themarinesurveyors.com

Don S/V ILLusion · Aug 11, 2020

Ralph Johnstone said:
Not disagreeing that the increased surface are will increase the potential, but how does it make the problem worse ?

I remember years ago being moored in a marina which doubled as a boat graveyard and in order to increase the short life expectancy of the two shaft zincs, I used to hang a 12" X12" zinc plate over the side and connect it to the shaft inside. Worked well 'til I got out of there.

Opinions vary but my understanding is simply that more anode can creates higher potential - the greater the V potential, the greater the rate of electrolysis. Unfortunately, the converse (less anode decreasing potential) isn't true except in a boat with zero voltage to ground initially - some voltage delta will always exist. Only after minimizing it should anodes be used sacrificially.
That advice is worth what you paid for it

Maine Sail · Aug 11, 2020

Two months is not normal. You'll want to find and fix the issue first...

Don S/V ILLusion · Aug 11, 2020

ontherocks83 said:
Everything electrical on my boat is new. Is there any design no no's I should double check, or is it more likely it's from another boat?

Could be a nearby boat, could be the marina wiring or could be something that is leaking (electrically) in your boat. I’d start with the bilge pump wiring and eliminate multiple ground points.

Davidasailor26 · Aug 11, 2020

Don S/V ILLusion said:
Opinions vary but my understanding is simply that more anode can creates higher potential - the greater the V potential, the greater the rate of electrolysis. Unfortunately, the converse (less anode decreasing potential) isn't true except in a boat with zero voltage to ground initially - some voltage delta will always exist. Only after minimizing it should anodes be used sacrificially.
That advice is worth what you paid for it

Voltage is determined only by the metals used, not the quantity. It may be possible to over-zinc and induce too much current, like some of Rich’s sources suggest, but I’ve seen two zincs used on a shaft without issue, so I suspect any over-zinc threshold is more than that. Using twice the mass of zinc should extend the protection for longer, but I agree with you and the other comments that two months is too fast to be going through a zinc, so that deserves attention.

jssailem · Aug 11, 2020

Here is one idea that might address your question...

Corrosion Reference Electrode (CRE) with User's Guide

www.boatzincs.com

Don S/V ILLusion · Aug 12, 2020

ontherocks83 said:
Is there a way to test if the leak is from my boat or another boat, before I start tearing through my whole electrical system?

Yes. Look for links about silver/silver chloride reference electrode - a cheap investment compared with the cost of a new prop.

jviss · Aug 12, 2020

I have a problem on my boat, too. My Max-Prop tailcone zinc disappears in one season, along with most of two zincs on the prop shaft.

I'm at a mooring, i.e., not plugged into shore power. I have an inverter that's used often.

One thing that troubles me is that the boat's bonding system is connected to the DC ground inside the boat, so if my understanding is correct, I have more than one electrical path to the water, i.e., the keel and the prop.

I probably should get the electrode @jssailem recommends:

jssailem said:
Here is one idea that might address your question...

Corrosion Reference Electrode (CRE) with User's Guide

Corrosion Reference Electrode (CRE) with User's Guide

www.boatzincs.com

Also, some general guidance one what should be connected to what, for "bonding system," DC ground, and AC ground.

By "bonding system" I refer to the connection of key structural elements of the boat with large-gauge bare copper wire: mast, keel, chain plates, etc.:

jssailem · Aug 12, 2020

You can test each of your metal systems with the "electrode" to identify (if) you have an electrical leak.
I call it low tech design (basic chemistry) - High Tech efficiency (quick way to identify which of the usual suspects is at fault).

jviss · Aug 12, 2020

jssailem said:
You can test each of your metal systems with the "electrode" to identify (if) you have an electrical leak.
I call it low tech design (basic chemistry) - High Tech efficiency (quick way to identify which of the usual suspects is at fault).

So, their user guide is not online; what would the strategy be, if you find a "leak:" start disconnecting things and note the change?

jviss · Aug 12, 2020

p.s. I just ordered the reference electrode and a couple more Max-Prop zincs. They are only a couple of towns over from me, I should have the stuff before the weekend.