# Prop shaft Zinc - how often?



## Dave_E (Aug 7, 2013)

Hi All,

Being a new "in the water boat owner" I have no idea how long your standard ball zincs will last. I have a 1" shaft and the PO has 2 ball zincs installed. He was paying for a diver but don't know if he was hauling out once a year. Here's my question.

A diver costs $100 + cost of the zinc(s). A haul and hang (lunchtime for the workers) cost $100... and I put on the zinc. I plan to haul and pressure wash annually on the 2 years between bottom paint. In your experience will 2 zincs last an entire year? My marina is brackish.

Dave


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## Faster (Sep 13, 2005)

In our experience the two shaft zincs do last a year, but I think it's a highly variable thing and tied to your specific boat/location/neighbour(s)/marina. Once you've got a season under your belt you'll have an idea..

We change them annually regardless.

btw.. if you have a mechanic's mirror on a stick and clear water it's surprisingly easy to get a decent look at the shaft zincs- at least to get the idea that they're still there.


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## boatpoker (Jul 21, 2008)

If your boat is in brackish water you should be using aluminum indium anodes, not zinc.


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## kentobin (Mar 31, 2007)

boatpoker said:


> If your boat is in brackish water you should be using aluminum indium anodes, not zinc.


I'd never heard of aluminum indium anodes before. Couldn't find any definitive information but some of the blogs indicated that zinc anodes were old tech and that the aluminum indium was good in both fresh and saltwater.

One blogger commented that the indium prevents the build up of an oxide layer on the anode and the aluminum indium is more environmentally friendly than just zinc. Allegedly the aluminum indium anodes are also 5% zinc.

Anyone have any good links with references for these anodes?

Back to zincs in saltwater. I have a large zinc attached to the side of my fiberglass hull with two bolts that hold it on that go through the hull. Wires run from the bolts and attach to the engine and a contact on the propeller shaft. The zinc must be at least 5"x8" and was 6 years old when I replaced it. My friends with external zincs on their propeller shafts replace them once a year.


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## boatpoker (Jul 21, 2008)

Zinc - salt water
magnesium - fresh water
aluminum - brackish water

Lots of stuff on line. google .... "anodes, aluminum, magnesium, zinc"
preferably get your info from US mil spec or manufacturers, not the usual internet guru's


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## Fstbttms (Feb 25, 2003)

Dave_E said:


> Being a new "in the water boat owner" I have no idea how long your standard ball zincs will last. I have a 1" shaft and the PO has 2 ball zincs installed. He was paying for a diver but don't know if he was hauling out once a year.


If he was paying for regular dive service, why would he haul annually?



Dave_E said:


> A diver costs $100 + cost of the zinc(s). A haul and hang (lunchtime for the workers) cost $100... and I put on the zinc. I plan to haul and pressure wash annually on the 2 years between bottom paint.


On what do you base your decision to clean the bottom only annually? Is that the norm in your area? It seems like that is not what the PO did.



Dave_E said:


> In your experience will 2 zincs last an entire year? My marina is brackish.


It is possible to get a year out of two streamlined collar (not "ball") anodes, but you should not expect it. I find 6-9 month anode life to by pretty typical here in the Bay Area. However you go about it, I recommend putting eyes on the anodes no less than every six months. Failure to do so could potentially cost you a lot more than a haul and hang and a set of anodes.










And as previously noted, in brackish water you should be using aluminim anodes.


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## Minnewaska (Feb 21, 2010)

Are you going to be in exactly the same marina as the prior owner? If not, your experience could be dramatically different. I've had the same boat go through several per year in one marina and almost get away with just one per year in another. 

Check regularly. 

Now a question for the FB. Do you notice that two shaft zincs provide much more time between needing to change than one? Anecdotally, I haven't.


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## Alex W (Nov 1, 2012)

Dave_E said:


> Being a new "in the water boat owner" I have no idea how long your standard ball zincs will last. I have a 1" shaft and the PO has 2 ball zincs installed. He was paying for a diver but don't know if he was hauling out once a year. Here's my question.


How long depends too much on your boat and where it is docked. If you have a nearby neighbor who's boat is wired incorrectly (or your boat is wired incorrectly) they can be eaten at a rapid rate.

On my boat, with a galvanic isolator and not using shore power at all in the summer months, I get 12-18 months on two 1" zincs. My boat was last hauled in Jan 2013, and was last dove in Jan 2014 (to install a new prop) and the diver reported that my zincs appeared to have more than half of their life left.



Dave_E said:


> A diver costs $100 + cost of the zinc(s). A haul and hang (lunchtime for the workers) cost $100... and I put on the zinc.


Where can you do a hang and haul for $100 in Puget Sound? Does that cover power washing and environmental recovery fees? On a 30' boat it would typically cost about $300 for a hang and haul with power washing. For instance at CSR it is $4.50/ft for the haul, $3.50/ft for the power washing, $50 flat fee for the recovery system, for a total of $290 on a 30' boat. Port of Everett looks like it is $4/foot + $2.75/foot power wash + $35 recovery fee for $237.50.

If you used ablative paint then you can't use a diving service to clean your boat. The fine for doing so in WA is $10,000. You can hire them to change zincs, and that is what many people on my dock do.

I recently bought a cheap underwater camera (Go-Pro-like) to make it easier to monitor my zincs.


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## Fstbttms (Feb 25, 2003)

Minnewaska said:


> Now a question for the FB. Do you notice that two shaft zincs provide much more time between needing to change than one?


In theory, two anodes should provide twice the protection that one does. And in my experience, that seems to generally be the case.


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## Alex W (Nov 1, 2012)

Is the primary downside to using multiple anodes increased drag? It would be nice if there were larger (longer) low drag anodes available that had the mass of two regular ones.


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## Minnewaska (Feb 21, 2010)

Fstbttms said:


> In theory, two anodes should provide twice the protection that one does. And in my experience, that seems to generally be the case.


I haven't often done so, but didn't think I got that kind of performance. We've been in the same marina for the past 4 years and I can come very close to making the season on one shaft zinc. I launch April 1 and haul Nov 1. I usually swap it in Aug and the next zinc is pretty good when hauled in Nov.

It would stand to reason, if I installed two zincs in Apr that I would make the entire season without worry. Maybe I will try, but I'm not super confident.

On the other hand, the zinc on the Max Prop goes faster and I can't add another. I don't really understand why, as it is in metal to metal contact with the prop shaft.

Stranger yet is the zinc on the Spurs shaft cutter doesn't corrode much at all, however, does get brittle and still needs to be changed annually.


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## Fstbttms (Feb 25, 2003)

Alex W said:


> Is the primary downside to using multiple anodes increased drag? It would be nice if there were larger (longer) low drag anodes available that had the mass of two regular ones.


My guess is that it would take very delicate equipment to dectect any increase in drag between a two-zinc arrangement and a single zinc setup. And considering all the variables that affect boat speed, the difference between having one or two zincs on your shaft is probably the last thing anybody should be concentrating on.

That being said, Martec produces a bullet-shaped zinc that some racers prefer over the streamlined collar type. I suspect it provides little-to-no advantage. I also believe they are made of an inferior alloy, as they definitely don't last as long as the mil-spec zincs I install.


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## Brent Swain (Jan 16, 2012)

In over 40 years of cruising I have never used a prop zinc, and have never had a problem. My engine is grounded to my steel hull, which has plenty of zincs welded on, and I don't hang out in marinas, with all kinds of AC fields around.


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## Dave_E (Aug 7, 2013)

Brent Swain said:


> In over 40 years of cruising I have never used a prop zinc, and have never had a problem. My engine is grounded to my steel hull, which has plenty of zincs welded on, and I don't hang out in marinas, with all kinds of AC fields around.


Brent, you know what apples and oranges are don't you?


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## eherlihy (Jan 2, 2007)

I started this season with 2 brand new CAMP zincs. I just had my boat hauled after 9½ weeks on a mooring in Greenwich Bay, RI. During that time I have not connected to shore power at all. This is what the zincs looked like. 

Yes, the water is brackish, but


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## Fstbttms (Feb 25, 2003)

eherlihy said:


> I started this season with 2 brand new CAMP zincs. I just had my boat hauled after 9½ weeks on a mooring in Greenwich Bay, RI. During that time I have not connected to shore power at all. This is what the zincs looked like.


I find Camp anodes to be inferior and I would never put them on a client's boat.


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## RegisteredUser (Aug 16, 2010)

Fstbttms said:


> I find Camp anodes to be inferior and I would never put them on a client's boat.


Being in the biz, what do you recommend?
At least those cheap anodes/bait were being eaten...rather than the boat.


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## eherlihy (Jan 2, 2007)

I totally agree about CAMP, but they are what I have... 

MUCH better value are B&S zincs.


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## Fstbttms (Feb 25, 2003)

RegisteredUser said:


> Being in the biz, what do you recommend?


In order of preference:

1.- Reliance
2.- Sea Shield
3.- Martyr (but only as a last resort)


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## overbored (Oct 8, 2010)

You should use Aluminum alloy anodes in Brackish water. work better and last longer Shaft Aluminum Anodes - Standard (X-1AL thru X-17AL)


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## SanderO (Jul 12, 2007)

I have never taken the boat out and had no zinc... completely corroded and gone in 32 years. I've seem some pretty intense corrosion but there was still zinc remaining. I do not spend time in marinas except for in water winter storage with a spring haul. Diver's reports are zinc are fine and I use a collar zinc. I am guessing your zinc's performance will depend on the salinity of the water and stray current or lack there of in it. If the zinc shows corrosion... it's doing its job.


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## eherlihy (Jan 2, 2007)

Before I launched this year I installed two aluminum Martyr brand sacrificial anodes. I've motored about 60 hours and the boat has spent the entire season on a mooring. I just had a short haul and powerwash done on my boat after 16 weeks in Narragansett Bay. The anodes were corroded so badly (90%) that I simply knocked them off with the handle of a wire brush. 

Is this normal?


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## chicory83 (Dec 21, 2009)

As noted above, the location and type of mooring can make a huge difference. On a mooring in Maine, my shaft zinc would last two six month seasons with room to spare. Connected to shore power at a marina in SF bay my max prop zinc was almost completely gone after three months. At this point I plan to install a galvanic isolator to see if it reduces galvanic corrosion, you may wish to consider that too. Unfortunately, my boat has custom sized zincs for the bonding system and I only have the facilities to fabricate them easily while I am in Maine, so I would like to have them last as long as possible - hence the interest in the isolator. I also decided to have the prop coated with prop speed to reduce barnacle growth, the yard owner commented that he thought that would extend the life of the prop zinc too. YMMV.


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## Minnewaska (Feb 21, 2010)

eherlihy said:


> Before I launched this year I installed two aluminum Martyr brand sacrificial anodes. I've motored about 60 hours and the boat has spent the entire season on a mooring. I just had a short haul and powerwash done on my boat after 16 weeks in Narragansett Bay. The anodes were corroded so badly (90%) that I simply knocked them off with the handle of a wire brush.
> 
> Is this normal?


I'm tied to a slip from Apr 1 to Nov 1 and can get away with one set of zincs that corrode by approx 70%. If I quick haul mid-season for any reason, I change them for good measure, but I often don't. I'm not sure what normal is, as there are many variables. Still, your experience seems excessive. The good new is, they're working! A DC ground leak would be the first thing I would try to rule out.


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## Fstbttms (Feb 25, 2003)

eherlihy said:


> Before I launched this year I installed two aluminum Martyr brand sacrificial anodes. I just had a short haul after 16 weeks in Narragansett Bay. The anodes were corroded so badly (90%) that I simply knocked them off with the handle of a wire brush.
> 
> Is this normal?


Assuming you are referring to shaft anodes, then what you experienced qualifies as rapid depletion. I would expect those anodes to last 6-9 months at a minimum and even then not be 90% depleted.


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## eherlihy (Jan 2, 2007)

Thanks for confirming my suspicion that this was not normal.

I spent a good part of today chasing the likely source of the ground leak. The leading culprit is the Iota DLS30/IQ4 Battery charger. I followed Niger Calder's troubleshooting flow chart: Start by disconnecting the positive lead from the battery, check for voltage between the + post and the cable, then check for amperage). Disconnecting the battery charger brought the ¼ amp draw to 0. I suspect that there was a ground leak through the battery charger's battery monitor circuit, which was then bleeding back through the battery charger's chassis ground (ground*ing* circuit in ABYC parlance), and then into the bonding circuit.

I have disconnected the battery charger case from the bonding/grounding circuit, and I pulled the battery charger's 30A fuse. Pulling the fuse proved to be impossible without destroying the fuse for some reason. Fortunately, I had 2 spare 30A fuses aboard. I will see if this helps alleviate the problem.


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## eherlihy (Jan 2, 2007)

... and this is what the two new Matyr aluminum anodes looked like after TWO WEEKS. The good thing is that this erosion shows that they're working!









Once again, this boat lives on a mooring, and not connected to shore power. It would seem like there is a voltage leak.

This boat has a PSS Shaft seal with a graphite bearing. To-date the PSS shaft seal has been awesome and I have a dry bilge! The downside is that graphite is a most noble substance, and may be contributing to the erosion of the shaft anodes.

Also note that there is no isolator between the engine and the prop shaft, so the prop shaft is indirectly connected to the alternator's negative lead. I am now considering placing a drive saver between the transmission and prop shaft coupling.


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## misfits (Dec 9, 2011)

I noticed the anode on my shaft was pretty toasted when we pulled the boat. I was in the water for 3 1/2 months & 
on a mooring. Took me by surprise, figured it would not have sacrificed as much. I have a isolated shaft because got an electric drive in her. The only thing the anode was protecting in theory is the shaft, strut & prop. DC electric is free floating unless grounding the solar controller to a keel bolt along with ac ground & lightning bond has created a problem. Now I'm thinking about grounding the 12 & 48 volt bank & removing the drive saver & see what she looks next year. Any thoughts?


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## GeorgeB (Dec 30, 2004)

eherlihy, is this boat in salt or fresh water? I would have thought that zinc would be more appropriate if the boat is in salt. Graphite is a electrical conductor and your DC system is grounded to the engine (as is the alternator). I get about three months on a shaft zinc and a bit more on the button zinc on the strut here in San Francisco Bay (I do keep my boat in a marina with lots of live aboards).


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## eherlihy (Jan 2, 2007)

Salt / brackish water in Greenwich Bay, RI.


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## Minnewaska (Feb 21, 2010)

eherlihy said:


> ... Also note that there is no isolator between the engine and the prop shaft, so the prop shaft is indirectly connected to the alternator's negative lead. I am now considering placing a drive saver between the transmission and prop shaft coupling.


I'm scratching my head over this point. Isn't it the case with virtually every drivetrain? Not sure it's your problem.


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## SanderO (Jul 12, 2007)

This is an interesting discussion. I use 30mm shaft zinc. Boat is wet stored and then on a mooring. I don't hang a zinc overboard. The zinc I use is a Beneteau donut. I don't use a battery charger to shore power. My solar panels keep the batts topped up and the starter batt is on an echo charge so it's almost always 100% for starting. As mentioned previously my zincs erode but last a year. Diver inspects and reports that is is OK. so I am not concerned. I am sure marinas often have stray current and this can be a problem... another reason to avoid them if possible.

eherlihy... how did you determine that Greenwich bay is brackish? I would think it would be considered salt water. If you are moored and losing zinc mass quickly you have some sort of fault in the ground system somewhere. What electrical device is left on all the time or a lot of the time. This would be where to start. 

Attached is the zinc on haul out after 1 year and wet storage. This is typical for my boat Shore power is only in winter when I am aboard and doing some project.


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## Minnewaska (Feb 21, 2010)

SanderO said:


> ....how did you determine that Greenwich bay is brackish?......


This is an interesting question, although, the Bay is not very saline throughout. Since it's fed by three significant fresh water rivers and I'm not sure how many brooks, the salinity of the Bay is just above the definition of saline, even near the mouth. Up by Providence, it's clearly brackish.

So, at any given point on the Bay, you could be right on the boarderline between brackish and saline, depending on tidal and river flow. Greenwich Bay does have a small fresh water tributary, so I'm not sure of it's actual level of salinity.

Personally, I use zinc, but I'll bet my marina is on the boarderline too.

Still, I'm not sure this is ultimately Es problem either. It reads like a DC ground leak. If he's on a mooring, it's unlikely from a neighbor or hot marina.


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## eherlihy (Jan 2, 2007)

SanderO said:


> eherlihy... how did you determine that Greenwich bay is brackish? I would think it would be considered salt water. If you are moored and losing zinc mass quickly you have some sort of fault in the ground system somewhere. What electrical device is left on all the time or a lot of the time. This would be where to start.


Devices that are constantly powered: AM/FM stereo (that I never use) memory circuit, Xantrex Echo Charge, Rule 2000 Bilge Pump and Ultra Safety Systems Ultra JR bilge pump switch. The bilge is totally dry by the way.

Below is a pic of the bilge, pump and switch (see the green LED on the switch), and a pic of the PSS Shaft Seal.


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## SanderO (Jul 12, 2007)

very impressive bilge. You must have a ground fault wired somewhere.


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## Don L (Aug 8, 2008)

Dave_E said:


> Hi All,
> 
> Being a new "in the water boat owner" I have no idea how long your standard ball zincs will last. I have a 1" shaft and the PO has 2 ball zincs installed. He was paying for a diver but don't know if he was hauling out once a year. Here's my question.
> 
> ...


2 zincs, plus my prop zinc, will last me 2 years. But, I also have Barnacle Buster coated my shaft and prop and think that this isolates a lot of the metal from the galvanic corrosion equation so the zincs last longer.

For you if you plan to haul and pressure wash every year just have the zincs on hand and replace if there is any question.

This is probably in the posts before this one, but I didn't feel like reading it all :laugh


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