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Old 02-07-2015, 09:57 PM   #41
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Don't believe it but we were told by the yard that once a zinc is out of the water it is no longer useable. Anyone else ever heard that? I'm talkin' salt water here.
This is 100% untrue. Because our harbor usually has a layer of fresh water on the surface, many of us hang a zinc on a cable (battery cable gauge) down about ten feet which puts it in normal salt water. The other end of the cable is connected to the boat's bonding system. This is because many boats like ours have transom zincs ("license plate" zincs) that are just below the surface of the water. This puts them in fresh water much of the time and they are not as effective. We pull the zinc up and stick it in a bucket on the aft deck when we take the boat out.

For our cable zinc we use old transom zincs that we get free from the dive service in our harbor. They are zincs they've removed from boats when they install new ones during scheduled routine hull checks and zinc replacements.

They don't last as long as a brand new zinc, but they're good for a couple of months and they're free. These zincs have been out of the water for months probably, in the recycle bin at the dive shop. They work every bit as well as brand new ones when we put them back in the [salt]water on the end of our cable.
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Old 02-08-2015, 12:01 AM   #42
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Ancora, I read through this thread and closely viewed your pictures.

IMHO:

- Take the plunge, so to say. Pull both props and get them checked out by a reputable prop shop. Then, take actions accordingly. That will be best for you in the long run (maybe in the short run too - ya just never know). A boat dollar or two or three at this time could save you many, many added boat dollars and a lot of headaches in the near or not too distant future.

- Place at least one and preferably two two zincs on each shaft, one on each strut and one on each rudder. Your bonding system helps... but is no where near as good as anodes' surfaces firmly attached to diodes' surfaces. Over zincing can be accomplished... but that is only under rare circumstances and with a hell of a lot more zincs than mentioned here.

- Go boating with peace of mind!

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Old 02-08-2015, 03:14 PM   #43
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A DMM can be used to check continuity of the zinc to the metal it is supposed to protect when the boat is out of the water. In fact the resistance should be checked. Failure to do that may result in a zinc just looking pretty yet doing nothing. If zincs have not degraded or minimally degraded then be suspicious.

Sometimes even what looks like a clean mounting surface is not as clean as you think. I DMM check all my zincs and sometime find that one of them, even though TIGHT on the shaft or the steel keel, is not actually in contact. I now take my grinder or Scotchbrite to the zinc surface, lightly, so it is bright, and if need be hit the mounting surface with a Scotchbrite pad, wire wheel or sanding disc as needed.

I check the prop to shaft resistance also although I've never had a problem there. Yet the possibility exists that even with a brush and shaft zincs that the connection will not allow them to work.

http://www.boatzincs.com/corrosion-reference-electrode-specs.html

will take you to a silver-silver chloride half cell that is used in conjunction with a meter to take voltage readings of the metals immersed in seawater.
There are voltage levels for bronze, SS, Alum., and steel and the reading will give you a good idea of how they and the zincs are doing.

You will need your own DMM, and a long ground lead that is used to touch the metals to get the reading. The CELL goes into the seawater.
I bought the meter kit years ago. I didn't know about Boatzincs at the time so spent a lot more money that I would have to now.
So assuming that most of us have a DMM and can cobble a 20ft probe lead this is one way to go.

I check my voltage levels at least twice a year. A couple of times I found a piece of metal that was not being protected so was able to take action rather than waiting to find out at haulout.

The setup can also be used to check for AC leakage. By disconnecting shore power and testing, then replugging shore power, if all is well than there should be NO change. If there is you may have a problem. You can also check to see if any AC ripple shows with a DMM which is another way.

I would get those props checked. Diver. But also ensure there is zincing that is actively protecting the props. They may be good with just a light pinking and if dealt with properly now could save you a bunch of money down the road.
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Old 02-08-2015, 04:55 PM   #44
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I also have the half cell that plugs into my DMM and use it whenever I cannot get the Ever-Guard meter to read in the green. High readings usually means I have to clean the shaft wipers. Sometimes the diver is remiss in his duty to replace the two plate zincs on the transom. I buy the plate zincs from Boatzincs.com and leave a pair of them in my open dock box for the diver.
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Old 02-08-2015, 07:33 PM   #45
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Great info. Thanks for sharing!


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Old 02-08-2015, 07:45 PM   #46
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I still had the stainless arms left to our shaft "brushes". I took an electric forklift motor brush (same as a starter brush) and epoxied it to the arm. I drilled a hole in the arm, and used a small bolt to fasten the pigtail from the brush to the bonding wire. Has worked fine (I guess) for a couple of years. Will shoot a pic Sunday when I go to the boat.


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Sorry- not a stainless arm. Here's the pics. Click image for larger version

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Old 02-08-2015, 08:08 PM   #47
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Quick test of shaft brushes is to put the DVM in volts and measure between bonding circuit and shaft. A good connection is in the few millivolts. 100+ mV and you have poor connection.

You can't test using ohm meter in the water as there is an impressed voltage.
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Old 02-08-2015, 08:08 PM   #48
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Sorry- not a stainless arm. Here's the pics. Attachment 37198Attachment 37199


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I would replace that connector with a marine grade heat shrink sealable one that won't corrode in a couple of months, to mention the wire which would have to be replaced too.
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Old 02-08-2015, 09:12 PM   #49
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Quick test of shaft brushes is to put the DVM in volts and measure between bonding circuit and shaft. A good connection is in the few millivolts. 100+ mV and you have poor connection.

You can't test using ohm meter in the water as there is an impressed voltage.

Ski, unfortunately all I have is an analog meter today at the boat. Will grab my Fluke when I return next and test as suggested👍

4712- that install is about a year and a half old- but will put the upgrade on my list.
Interesting story- recently at the local chandlery here in Gulfport I was asking for some bronze cotter pins (still had original ones installed) to secure the handles on the tapered cone sea cocks I am lapping in tonight. Poo Hoo I was told. Doesn't matter. I encouraged him to check in the Donovan Marine catalog- and none available. Went home with SS ones which I will install tonight.
All that to mention that last weekend in preparation for the bottom job I am having I was removing the "clam shells" that I could, the one for the AC strainer (apparently added later) one was actually secured to the mushroom head, as a set, with countersunk SS machine screws. And no problem to remove after all these years. Who woulda thought it??


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Old 02-08-2015, 09:56 PM   #50
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I'm not so sure that's the case, Scott, otherwise there'd be a lot of unhappy fishermen about! :-) it's a pretty common procedure around the commercial waterfront. One would think that otherwise there would be a problem with oxidation of a lot of props out there. Murray would have learned this procedure from veteran shipwrights 35 years ago when he apprenticed with Canadian Fish. I've watched him do this and the slag separates from the liquid metal.


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Ok, boats cost money, zincs are.... well cheap in the overall scheme of things.

Fisherman are cheap, I know, I am one and when I ran a commercial boat (Dive) I was the cheapest. Now I think I will buy zincs that are Mil-spec and new. Your mileage may vary.

Regards
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Old 02-10-2015, 11:24 AM   #51
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Not so pretty in pink...

I stand corrected: I phoned my shipwright last night to discuss the process he uses for the zinc on the prop nut. Murray uses a new prop zinc, of a type that must be installed using molten zinc. It has a hole on the top to introduce the molten zinc. I had thought he was using a mold, but actually tongs were used to hold the zinc in place during the process. He's agrees that prop zincs that are 50% spent are compromised metal.

The reason for this more involved procedure is because the troll fishermen are concerned about the electrical potential of the fishing gear. Fishermen WANT to maximize the electrolysis of that zinc and they test the voltage gradient between the rudder and the fishing lines on the gurdies. Sometimes he uses spent zincs as a source of metal for the molten zinc and sometimes he uses new zinc-it's the fisherman's choice. Tuna fisherman are especially concerned about the electrical fields around their fishing gear.

I had forgotten that about 40 years ago, there was a lot of speculation about the effects of weak electric currents on the fishing catchability of fishing gear. A co-student of mine, Dan Nomura did his masters thesis on this area of research: "The effect of weak electrical fields on troll success for spring (Oncorhynchus tschawytscha) and sockeye (Oncorhynchus nerka) salmon." Fishermen used so called "black boxes" to control the voltage gradients between the fishing gear and the boat. The results demonstrated significant increased fishing success in certain situations, see reference for details. Incidentally Dan went on to become president of Canadian Fishing Company.

https://circle.ubc.ca/handle/2429/21785?show=full



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Old 02-12-2015, 01:26 PM   #52
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Pictures: the wipers on our twin screw trawler, along with the Ever-Guard meter and test gear. The only problem with Ever-Guard is not the system itself but ignorant divers who do not have a clue how it works, and want to add zincs.
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Old 02-12-2015, 01:44 PM   #53
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Ancora- If your props are pink due to de-zinc'ing in the alloy, your Ever-guard system is not working, somehow.
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Old 02-12-2015, 08:14 PM   #54
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IMHO and going back into the 1950's. Boat repair yard On LI, NY had a great sign over the door:


Zink or Sink!


True then... True today.
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Old 02-12-2015, 08:24 PM   #55
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Boat poker, sorry I don't quite follow. I know if I want to be sure my prop shaft has continuity through the brush and to the bonding wire I would measure resistance between the shaft and the bonding wire. Is that what you mean? I wonder if there is an easy way to be sure there is minimal resistance from say- the prop shaft to the big zinc block ?


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1. Then simply measure between the shaft and to the point where your brush is bonded.

2. Measure between the shaft and the "big zinc block"

A few years ago I walked around a boat yard and measured resistance between shaft anodes and shafts. Out of 40 boats I found only two that had good continuity. One was a new boat that had never been in the water and one had just had a new anode (properly) installed. If your anode is not dissipating it is not working. Most people install anodes without ensuring continuity. The surface on which the anode is mounted must be cleaned and there must be good electrical contact between the two. Taking a wire brush to an anode is simply not good enough.
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Old 02-12-2015, 10:30 PM   #56
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Ancora,
Ski is dead on.

Your Ever guard is not protecting the props. It may be working for other things but that pink says the props are not protected.

It may simply be that the shaft brush is not in GOOD or GOOD ENOUGH contact or the wire from the brush has a problem.

Even a wee bit of oxidation at the wire terminals or the terminal crimp barrels can cause trouble. The voltages are very small so ANY resistance can block the protection.

Check it out.
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Old 02-13-2015, 03:54 AM   #57
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1. Then simply measure between the shaft and to the point where your brush is bonded.



2. Measure between the shaft and the "big zinc block"



A few years ago I walked around a boat yard and measured resistance between shaft anodes and shafts. Out of 40 boats I found only two that had good continuity. One was a new boat that had never been in the water and one had just had a new anode (properly) installed. If your anode is not dissipating it is not working. Most people install anodes without ensuring continuity. The surface on which the anode is mounted must be cleaned and there must be good electrical contact between the two. Taking a wire brush to an anode is simply not good enough.

Well noted. I'm finally getting back to the boat today and the yard will have the zincs installed- I will confirm continuity with my Fluke. Thanks


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Old 02-15-2015, 02:14 PM   #58
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I took some readings today, and they were abnormally high. Cleaned off the shaft wipers and the readings went down to "acceptable." Gonna have to keep a closer eyes on them wipers.
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