Checking zincs - how often?

S

sparky

Well-known member
Joined
Jan 8, 2009
Messages
215
Fluid Motion Model
C-32 C
Hull Identification Number
FMLC2413G617
Non-Fluid Motion Model
36' Endeavour Trawler Catamaran
Vessel Name
MoonBeam
For those of you who keep your boat in the water, how often have you been looking at your zincs, and more importantly, how long/short of an interval between replacing them? After 7 months our diver reported our prop zinc was completely dissolved, but the bow thruster and trim tab zincs were still over 50%. (He could not visualize the stern thruster zinc because of the housing.) We are in a salt water marina. We are changing marinas and plan on having our diver visit every two months for now but are interested in the experience of others.

Sparky 😱
 
I have been replacing by prop zinc and trim tabs every 9 months in salt water. The thruster zincs seem to last longer. I am seriously considering using a guppy zinc which you ground and then throw over the side of the boat. My marina is known for being hot.
 
The standard answer - is that it all depends. If you plug in to shore power, and there is stray current - you'll be lucky to get 3 months. A large marina, with plenty of boats (all with zincs), and with a galvanic isolator - 6-9 months. An electrically quiet location, or not plugged in - a year or more? 'course this is in the cold waters of the Pacific Northwest...

Although the trim tabs are electrically connected (bonded to the ground system)- they do so through the metal hinge of the tab. That's not always a reliable conductor, so you can't rely on the trim tabs as a gauge.

I started at 3 months, although I think my prop nut zinc fell off more often than it dissolved away. I'm now running 6+ months, and the zincs are still doing OK. I try not to plug into shorepower, have added an isolator for those times when I do, and most often utilize a zinc guppy over the side when at the marina.

Mac
 
Mac
I am sure I am not the only one who would like to know more about your "Guppy Zinc." I have been thinking of something along these lines but really don't know HOW to make one or what to ground it to. Help! and Thanks!

Monika
 
Thank you Mac. One more question (since my brain is still on all the income tax returns on my desk), what are you clipping it onto?


Monika
 
Now that's a good question. I have always clipped it onto the ground strap right at the battery. But, looking at the ad in the catalog,I noticed that it says "do not attach to the battery ground" . I wonder why?

I started to ask around in class (I'm taking a Coast Guard Search, Coordination and Execution / SAR class) today - some people clip to the engine block, others attach to the negative battery terminal (like me). I'll keep searching, but for now, I would connect anywhere on a ground wire.

Mac
 
I'd agree that the guppy (oops, I guess it grew up to be a grouper) I got from West Marine doesn't seem to be the same quality as I remembered from "the old days". But it is wearing fairly uniformly, and it has a ton of zinc compared to the amount mounted on our boats (prop nut/trim tabs). So without an alternative, I'd continue to use it. I think I have ~ 1 year on mine so far and it is holding up OK....

mac
 
One note on zincs. The zincs made in Canada seem to go away quicker and I think that is a good thing.
Bob Heselberg Eatonville Wa
 
After about 7 months at a Tennessee River marina my zincs all looked like new. I even removed zincs & checked the weight compared to new replacements I had bought. Except for the GENSET pencil zinc in the air cooler which was completely gone. I assume must be due to the river water and lack of stray currents at marina. Not sure why GENSET zinc was so differnt but my plan is to check this often. Easy to check due to good access to zinc

My boat did not have OEM zincs on trimtabs so I installed them this winter.
 
OK...I'm gonna guess that the Tenessee river is fresh water. Zinc isn't really the correct sacrificial anode - I think you need magnesium, right?

Here's what I read:
Generally speaking, zinc anodes will provide good protection in both salt and brackish water. Do not use zinc anodes in fresh water. When used in fresh water, the zinc tends to passivate, that is, it forms an insulating film of zinc hydroxide that prevents it from functioning as a sacrificial anode.

Mac
 
Here is a scary one: We had our prop zinc replaced last week. We changed marinas on Sunday. The diver went to pull our mildly corroded prop off today so I could get it reworked, and said the zinc he put on last week is already significantly eroded. ONE WEEK. Now we don't yet know if the problem is marina #1, marina #2, or the boat itself. This should be fun.

One very important and expensive lesson we have learned this week: should'a checked the zincs earlier...

Sparky
Virginia Beach
 
I found the below bit of information about Aluminum Anodes at:

http://www.boatzincs.com/grouper.html

"Three pound overboard aluminum anode with 15 ft. vinyl coated galvanized steel cable and electrical connector for grounding.

This Grouper features Mil-Spec A-24779 (SH) aluminum alloy with a galvanic voltage of -1.10v in seawater to offer the highest level of corrosion protection possible for a vessel while at the dock. Simply attach to the vessel’s DC ground and hang overboard. It’s a very effective solution to extending the life of your boat’s zincs."

The R-25's green wire bonding system is connected to all of the negative battery posts.
Henry
 
sparky":3qhdbdt7 said:
Here is a scary one: We had our prop zinc replaced last week. We changed marinas on Sunday. The diver went to pull our mildly corroded prop off today so I could get it reworked, and said the zinc he put on last week is already significantly eroded. ONE WEEK. Now we don't yet know if the problem is marina #1, marina #2, or the boat itself. This should be fun.

One very important and expensive lesson we have learned this week: should'a checked the zincs earlier...

Sparky
Virginia Beach
Click to expand...

Sparky, while docked are you connected to shore power? If so and you do not have a Galvanic Isolator connected to the 110V green ground wire, chances are that these is a healthy current flow in the wrong direction through the green ground wire that is causing your zincs to rapidly disappear. Once the zincs are gone electrolysis will attack all of the underwater metal that is connected to the boat's bonding system! See the below from http://www.yandina.com
Henry

"If other currents are allowed to get into the bonding circuit they can easily overpower the small voltage available from your zincs and defeat the protection you need. This is usually the most destructive form of electrolysis and you notice it because your zincs get eaten up very quickly trying to keep up. Under normal circumstances, zincs should last at least a year if they are working normally, and much longer if you don't have any problems. If they are being "sacrificed" in a shorter period you need to find where the external current is getting in.

The most common source of this external current is the shore power connection, especially the green ground lead. Docks are notorious for bad wiring and often the ground lead is not connected to ground, is connected to the neutral, is being used for carrying current to a mis-wired boat, and all other sorts of problems. So the ground lead should never be directly connected to the ground bonding system we talked about earlier. The purpose of the shore power ground lead is to provide a return path for current if there is a short circuit or power leakage from an appliance or the wiring on the boat. You don't want it to connect all the underwater items on your boat to the underwater items on all the other boats and the dock because now your zinc is trying to protect everyone else too.

Unfortunately it is not always possible to keep the circuits separate due to interconnections such as shore power chargers. There are a number of ways to separate the shore power ground from the boat's underwater bonding system. The preferable and safest way is to use a galvanic isolator to introduce a 1.2 volt insulator in the circuit. This is enough to isolate most galvanic voltages but it will still conduct electrical faults and keep the boat safe in the event of a ground fault in the wiring or in an appliance. The galvanic isolator must be rated for the size of your shore power circuit."
 
Henrym
Thanks for that great explanation. We have been doing research and reach the same conclusion, that we need to install the galvanic isolator. I just have to wonder though, since many of us stay in marinas and Ranger set up this lovely shore power connection, WHY a galvanic isolator isn't either standard issue or at least an option available from Ranger. Not very happy about this one.....

So, anyone want to suggest exactly what unit to purchase?
Thanks all,
Sparky
 
The price of Galvanic Isolators is from about $100 to over $300. Below is one selling for $96.99. Galvanic Isolators are not that difficult to install, "1. Mount the isolator inside the vessel to any convenient surface within about 15 inches of the shore power entry connector using the screws supplied. The maximum ambient temperature should not exceed 122EF or 50EC. 2. Disconnect the shore power cord to prevent electric shock while working on the connector. 3. Remove the existing ground wire from the shore power connector. The ground wire should be green, or green with a yellow stripe. If there is any uncertainty to which is the ground wire, get competent help before proceeding. 4. Connect either of the green leads from the isolator to the vacated terminal of the shore power connector. 5. Connect the other green lead from the isolator to the vessel ground wire you removed, using the compression connector supplied. Shorten the leads if necessary. 6. Dress and attach the wires so they are firmly fastened."
Henry

http://www.defender.com/product.jsp?pat ... &id=605562
 
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