Hi! I'm a new owner of an '84 MK-I c36, and I'm a bit concerned about my zinc depletion rate. The boat is in salt water, and during my purchase haul out eight weeks ago, I replaced the prop cone, on of the two prop shaft zincs, and the strut zinc. I also installed a pro safe galvanic isolator about three days after I purchased the boat and verified that it is indeed isolating the boat.
I just had my first bottom cleaning and the diver replaced all of my zincs except for the strut pancake which he claims was down to 75%. This was only an 8 week soak! Is this typical, or did I just pay diver welfare??? Is it possible that I have too many zincs??? I have ordered a half cell and plan to test next week. But I'm just wondering if people are having to replace them that often, and how many zincs you have on your boats?
Ellsworth Wente
S/V Wind Dancer, C-36MkI hull #256
I have a fixed 3-blade bronze prop and bronze shaft. My only underwater zinc is the torpedo zinc on the shaft. The boat is in slightly brackish (more salt than not), warm water all year. I do not plug into shore power hardly at all since I have lots of solar panels keeping the batteries charged.
With the above situation, I replace the shaft zinc perhaps 2-3 times per year.
Duane Ising - Past Commodore (2011-2012)
s/v Diva Di
1999 Catalina 36 Hull #1777
Std rig; wing keel, M35B, Delta (45#)
Punta Gorda, FL
http://www.sailblogs.com/member/diva-di/
I'm no expert on the subject, but it sounds like you (or a slip neighbor) could have a problem with the electrical system, that is putting current into the water, possibly through your propeller shaft. I read about this several times in the past, but don't recall the details. I found this article which may help.
[url]http://www.stevedmarineconsulting.com/ezine/index.php?p=40[/url]
Maybe an expert like Mainsail will add his expertise.
Gary and Cathy Price
1997 C36 Mk II Tall Rig/Wing Keel Imagine...
Hull # 1617
Worton Creek, Md.
Northern Chesapeake Bay
Good advice from Gary. Something to look into. It's covered quite well in Nigel Calder's book, Boatowners Mechanical & Electrical Systems. I have a strut zinc and a shaft zinc. They get replaced about once every six months.
Don't forget the one in the HX.
Good luck.
Stu Jackson, C34IA Secretary, C34 #224, 1986, SR/FK, M25 engine, Rocna 10 (22#)
I suspected that stray current problem... And, when I bought the boat, I found that there was a 30 year old galvanic isolator behind the electrical panel which the previous owner didn't even know he had. The battery charger was grounded to the wrong side, effectively rendering the isolator worthless. So, 3 days after the purchase, I installed a brand new isolator, that is wired correctly, and basically corrected the problem. The dive service, who I immediately fired, had spoken with the diver my previous owner was using, and I suspect determined my rate of replacement from that discussion, rather than reality. It sounds like losing 3 zincs in 8 weeks is unheard of. But again, I'm wondering if having too many zincs could cause a rapid depletion? My thinking is, the previous owner didn't know why they were depleting so much, so he just kept adding more zincs. Now, I think I may have too many... Does anyone know if rapid depletion a symptom of having too many zincs?
Ellsworth Wente
S/V Wind Dancer, C-36MkI hull #256
I agree that this is probably stray current, possibly from the AC line into the boat.
That was the case on my boat - same year as yours.
See here for details of how I solved this with the half-cell:
[url]http://www.c36ia.com/forums/showthread.php?t=2228[/url]
Ever since I removed the tie from ac neutral to ac ground inside my boat, my zincs have been depleting quite normally, so I'm pretty sure that was the cause/solution.
You may want to just check that before investing in the half-cell.
I don't remember Calder talking about this particular issue. I got the hint from the half-cell manual: It says that the older style reverse polarity indicators are low-resistance. That's what causes the significant leak from neutral to ground.
Newer electrical panels apparently have high-resistance indicators? or some other solution.
Ben Ethridge
Miami, FL
1984 MK1 Hull# 263
Ben, thanks for that input.
Ellsworth, Calder DOES cover it in quite some detail. One of things that may people miss is the older galvanic isolators fail without any warning. The newer ones may have "Idiot Lights" to tell you that they failed.
Stu Jackson, C34IA Secretary, C34 #224, 1986, SR/FK, M25 engine, Rocna 10 (22#)
Hi, Stu. Yes, he talks about the stray current issue quite a bit. I just meant that he didn't talk about the particular issue of low resistance reverse polarity indicators as a cause of stray current....not that I remember anyway.
I didn't know to look for that particular one until I read the half-cell manual.
But then, that manual was $80...which now makes this forum quite a bargain. :)
Ben Ethridge
Miami, FL
1984 MK1 Hull# 263
Thanks for the suggestion Ben, I'll check around for parasitic AC leaks. I have installed a brand new set of electrical panels with an LED based reverse polarity indicator which I would expect to be high impedance. It's possible that the old dorm fridge or the microwave could be leaking/bonding neutral to ground, but again, the shore power ground is going through a brand new isolator. I suppose if there's enough AC leakage on the neutral it could push the isolator diodes into conduction and render it ineffective. I'll let you guys know what I find if I make it down to the boat this weekend.
Thanks! Ellsworth
attaching a pic of my new panel:
Ellsworth Wente
S/V Wind Dancer, C-36MkI hull #256
BTW - if any of you decide to do a panel upgrade, black chalk board from home depot for ~$5 makes a great replacement for the old fiberglass. You can cut out the holes in it, and mount all your new goodies and have plenty left over!
[url]http://www.c36ia.com/forums/images/smilies/biggrin.gif[/url]
Ellsworth Wente
S/V Wind Dancer, C-36MkI hull #256
So yesterday, I received my half cell and ran down to the boat. I found that the zincs were protecting at -965mV (which means I'm not over zinc'd) I tested my galvanic isolator, and it's working fine. Following the testing guide that came with the half cell (connecting shore power, powering up DC circuits one at a time, watching for change in galvanic potential, etc). I'm not finding any problems... I do still need to go back and fire up the engine to see if maybe the alternator is introducing stray current, but basically, I'm not seeing any stray current leaks at this point. Next step, I suppose, is to dive into the frigid water and check the anodes/wait a few months and see if they deplete. Really suspicious of the diver now. My slip neighbor said he's swapping zincs every 4-6mo and he dives his boat himself.
Ellsworth Wente
S/V Wind Dancer, C-36MkI hull #256
Probably not the panel I mentioned, since yours is new.
A couple of thoughts:
1. Mark your zincs with an identifying mark that is subtle enough so the diver won't notice?
2. The manual talks about taking a baseline measurement with the half cell with EVERYTHING unhooked, i.e. shore power unhooked and 12v batteries unhooked. Then you start adding stuff back into the system and see how much it affects the meter. That was part of your testing, right?
3. Are your zincs corroding but shiny? Mine were and that is one indication of stray current leak, as I recall from Nigel Calder. If not, I'm leaning toward the diver...or A diver.
Ben Ethridge
Miami, FL
1984 MK1 Hull# 263
[QUOTE=ewente;19442] It sounds like losing 3 zincs in 8 weeks is unheard of. [/QUOTE]
Not unheard of, just unusual. And considering the state of the electrical system when you bought it, it seems entirely possible that there could be another undiagnosed electrical problem aboard your boat. Much more likely a scenario than a hull cleaner risking losing a client simply to make a few extra bucks. Further, a diver would have to be pretty stupid to assume you wouldn't question the replacement of three brand new zincs, unless he could back it up. In the future, consider asking your diver to leave the zinc remnants on the dock for your inspection (which should be part of the service anyway, IMHO.)
[QUOTE=ewente;19442]But again, I'm wondering if having too many zincs could cause a rapid depletion? My thinking is, the previous owner didn't know why they were depleting so much, so he just kept adding more zincs. Now, I think I may have too many... Does anyone know if rapid depletion a symptom of having too many zincs?[/QUOTE]
Rapid depletion is not a symptom of having too many zincs. It is, of course, possible to over-zinc, but typically in such a situation you would see problems with the anti fouling paint and not with the zincs.
In my experience, with the correct compliment of zincs attached, you should get 6-9 months life out of them, and hopefully it would be towards the longer end of that scale. If you find yourself getting dramatically more or less life from your zincs, it's time to find (and solve) the problem.
Clean bottoms are FastBottoms!
[QUOTE=fstbttms;19724]
In my experience, with the correct compliment of zincs attached, you should get 6-9 months life out of them, and hopefully it would be towards the longer end of that scale. If you find yourself getting dramatically more or less life from your zincs, it's time to find (and solve) the problem.[/QUOTE]
Wow, I get a couple of years from mine. The boat is in salt water too.
Sent from my iPad using Tapatalk HD
Cat375 - Rock The Boat - Hull 54
Lake Macquarie - NSW - Australia
[QUOTE=Rockman;19751]Wow, I get a couple of years from mine. The boat is in salt water too.[/QUOTE]
I'm not sure that's necessarily a good thing. I mean if you electrically unhook the zinc altogether, it will last thousands of years.
It may not be doing its job of sacrificing and saving the other metals.
Mine lasts about 3 months.
You sure it has a good, solid electrical connection?
Ben Ethridge
Miami, FL
1984 MK1 Hull# 263
Just as two years is probably longer than proper functioning zincs should last, three months is too short. That is very rapid zinc depletion.
Clean bottoms are FastBottoms!
Even for one little egg zinc on the prop shaft? ...and it's not shiny?
Ben Ethridge
Miami, FL
1984 MK1 Hull# 263
[QUOTE=benethridge;19774]Even for one little egg zinc on the prop shaft? ...and it's not shiny?[/QUOTE]
Yes.
Try adding another shaft zinc and see what that does for your zinc longevity.
Clean bottoms are FastBottoms!
Sadly, I really think my zinc replacement rate was definitely a "diver welfare" situation. My half cell with all power disconnected reads a protection level of -965mV, which is where it should be. I did verify the electrical system by powering up each branch circuit (both the AC and the DC systems) one at a time, and I watched for any galvanic voltage changes. And I have checked that my new galvanic isolator is indeed isolating. So at this point, I'm keeping an eye on it, and will send the go-pro camera down on a stick to do a visual. But for 3 brand new zincs to disappear in only 8 weeks, it's basically down to an unscrupulous diver I'm afraid. I currently have a cone on the prop, a pancake on the strut, and two shaft zincs. I just replaced my heat exchanger pencil which was consumed down to about 50%, and it lasted 6 months (since the previous owner had the heat exchanger refurbished last April)
Ellsworth Wente
S/V Wind Dancer, C-36MkI hull #256
Well, in any case you might consider asking your diver to leave the remnants of any replaced zincs for your inspection.
Clean bottoms are FastBottoms!