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Old 10-12-2015, 06:03   #1
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grounding a boat from stray currents

I have had an issue with going thru zincs on my cat. I have installed a galvanic isolator but was wondering if a "fish " [anode on a line] put over board would also help?
Thanks for any Help
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Old 10-12-2015, 06:25   #2
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Re: grounding a boat from stray currents

Pretty controversial to be honest, first if it is not bonded to the underwater metals a fish will do nothing at all but waste money.
I use one for two reasons,
1. it does provide more sacrificial anode, so more metal to be wasted away before the expensive bits.
2. Primarily though I use it as a witness, that is if it suddenly starts eroding at a faster rate, well then something has changed and maybe I got enough warning to do something about it before it's too late, I see the fish before each sail, I see my uinderwater anodes not as often as I should.
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Old 10-12-2015, 08:09   #3
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Re: grounding a boat from stray currents

Do you attach the the fish to the mast ?
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Old 10-12-2015, 08:26   #4
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Re: grounding a boat from stray currents

Grounding and bonding can be a confusing subject and there are many on the forum with much more expertise than I can offer. I can however speak from experience.
During the course of re-wiring my entire boat, I had not yet fitted bonding wire to all of the underwater metal. My sail drive zincs on my cat were lasting just a few months. I have now bonded everything together, it is the only change that I made and it made an instant difference; the zincs are still good after nine months. I also fitted a fish which I made myself. I used a 8 x 4" plate of aluminum and attached to it a rudder zinc. The plate has a steel vinyl-coated wire attached to it (with the vinyl coating removed at the attachment point). At the other end of the wire I fitted a large alligator clip. The whole thing cost about $40 to make. The bonding wire on the inside of the boat is connected to a bolt which runs through the hull in a discreet location on the sugar scoops. It is then a simple matter of pulling out the bolt and clipping on the alligator clip.
As 'pilot' says, every time I go sailing, I pull the zincs out of the water and it's much easier to check their condition and to replace the zinc when necessary than doing so on my drives.
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Old 10-12-2015, 09:38   #5
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Re: grounding a boat from stray currents

I also use a zinc 'fish' at all times when the boat is in a marina. Since I had previously grounded my lifeline stanchions (for lightning and RF grounding reasons) on the inside where the bolts run through the deck, I attach the wire coming from the fish to one of the stanchions - you could use either a hose clamp or battery jumper clamp for quick disconnect.


You don't really need a separate plate to mount the zinc on. I get the zincs that have an embedded copper wire and then solder (best) or use a crimp terminal butt connector to attach a large gauge stranded wire to the zinc wire.


Ditto on what a54pilot mentioned about the zinc as a 'witness'.


BTW if your zincs disappear too fast and you are interested in further education on the subject, you can read about using a digital voltmeter to measure the potential between various points in your ground system. It is interesting to measure the voltage between your fish and the AC ground coming to the boat from the marina.


There's plenty of good info on this on the web - I did this years ago and can't remember the sources I found.
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Old 10-12-2015, 09:51   #6
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Re: grounding a boat from stray currents

The fish seems to help many in hot marinas. Each case is different I suppose. I see no downside to trying it.
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Old 10-12-2015, 09:55   #7
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Re: grounding a boat from stray currents

Another endorsement for use of the fish with the stanchion post.
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Old 10-12-2015, 09:58   #8
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Re: grounding a boat from stray currents

Marine Grounding Systems | West Marine
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Old 10-12-2015, 10:25   #9
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Re: grounding a boat from stray currents

I haven't seen any harm myself in using a fish zinc. But it is entirely possible to "overzinc" your boat. More is not better in that case. If you don't have a problem with your zincs now adding another zinc isn't going to give you more help. If you are underzinc'ed it would help, but generally speaking you want the area that needs to be protected to be protected locally and not far away.

I'd be very nervous if the fish zinc were to be the only thing deciding whether my boat bits corrode or not.

However, this is a poorly understood and controversial issue. There is science and practical knowledge available and every sailor should read up on it but don't assume any one source is the bible on the subject.

The best advice I have ever seen is to bond everything or bond nothing. I have bonded many, many boats professionally but I won't anymore. The bonding systems always fail at various points. But I would zinc the parts that stick out in to the water that are in electrical contact with the rest of the boat - prop shaft, rudders (sometimes), prop.

If you do use a fish zinc, I would definitely be nervous if I found it eaten up faster than normal in one place or another but would also worry that my own boat had had a change somehow.
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Old 10-12-2015, 11:27   #10
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Re: grounding a boat from stray currents

Maxi racing boats will use zincs attached to wire that is in turn clipped to the shrouds when they are in a marina. Provides an absolute ground to the boat as well as dealing with ground faults in marina wiring. BTW,never assume a marina is correctly wired, especially in terms of the ground.
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Old 10-12-2015, 11:48   #11
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Re: grounding a boat from stray currents

Quote:
Originally Posted by Stu Jackson View Post
Stu, a good write up. I would have to read it more closely but it appears to have a bit of paradox in it. Aside from that it almost sounds as if, grounding to a keel bolt could make the ballast sacrificial? I can see it as a lightening ground but not for an electrolysis cathode? I have yet to figure out what the one isolated GFI was for the way it was depicted for a hot marina?
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Old 10-12-2015, 12:16   #12
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Re: grounding a boat from stray currents

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Originally Posted by sailorman7225 View Post
Another endorsement for use of the fish with the stanchion post.
But what is the station attached too? If not, it is does nothing for the boat.
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Old 10-12-2015, 12:19   #13
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Re: grounding a boat from stray currents

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Originally Posted by waterman46 View Post
I also use a zinc 'fish' at all times when the boat is in a marina. Since I had previously grounded my lifeline stanchions (for lightning and RF grounding reasons) on the inside where the bolts run through the deck, I attach the wire coming from the fish to one of the stanchions - you could use either a hose clamp or battery jumper clamp for quick disconnect.


BTW if your zincs disappear too fast and you are interested in further education on the subject, you can read about using a digital voltmeter to measure the potential between various points in your ground system. It is interesting to measure the voltage between your fish and the AC ground coming to the boat from the marina.


There's plenty of good info on this on the web - I did this years ago and can't remember the sources I found.
You can measure the voltage difference between your bonding system and the water using a corrosion reference electrode and verify if you are correctly 'zinced'.

Corrosion Reference Electrode Product Specifications

"
"The Corrosion Reference Electrode is an extremely useful test and diagnostic tool that should be included within the toolbox of every boater and marina operator. When plugged into your digital multimeter you get answers to questions such as:

"Do I have enough zinc on my boat?"
"Are my shaft zincs still attached?"
"Is my bonding system working okay?"
"Are boats next to me eating my zincs?"
"Is my galvanic isolator working?"
"Is all of my electrical equipment installed correctly?"
"Do I have stray electrical currents either in my boat or at my dock?"
"Is my dock and/or marina operating at the correct corrosion potential?"
"
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Old 10-12-2015, 12:50   #14
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Re: grounding a boat from stray currents

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Originally Posted by Celestialsailor View Post
But what is the station attached too? If not, it is does nothing for the boat.
Agreed, mine is attached to the engine block, then almost everything on the boat is attached to the engine block. I clip my fish to a stanchion also, but only because it is bonded electrically, pretty much my entire boat is, and has been since it was built.
It seems bonding or not, both have failures, if like my boat has had no issues, I wouldn't change things, meaning if she has had no problems and is un-bonded, I don't think I would change things, unless I was seeing a problem.
I do not understand exactly how, but I have seen enough problems in a Marina to believe that a new neighbor's boat and or the Marina electrical system can cause problems, I hope my fish would warn me in time before my really expensive Autoprop is eaten up.
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Old 10-12-2015, 14:20   #15
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Re: grounding a boat from stray currents

The best solution is to install a grounding plate to the hull and run all your grounding straps to that. A lot of boats tie in the straps to the engine block, but that can lead to some issues. Tying into the keel works only if the keel is external and made of lead and your bolts are monel. In any event, lightening will likely punch holes in your boat regardless of grounding or not grounding.
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