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Old 09-19-2017, 10:49 PM   #1
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Zincs working?

Recently during the annual 'Shave and Haircut" haul for bottom paint and zincs the condition of the zincs were determined to be good enough, with the exception of the shaft collar zinc, to go another year. Great news!! Considering that the prior annual found the zincs on the last legs of being physically in their location. The hub cap zinc was almost the monel bolt!
So what has happened to reflect this vast difference?
There has been no phyical change in the harbor, or boat slip changes during the year. No electrical systems in the harbor have be touched. In effect all the normal suspects are not present.

Okay- Now. Having in the past year, learned more about changing out the zinc anode located in the engine cooling system I had set a schedule of every 6 months change it out. At the first six months there was nothing left on the anode, so I changed the schedule to 5 months. At the end of the 5th month yesterday, I changed the anode. There remained less than a 1/4 inch of zinc.

So- If my zincs on the boat proper are remaining in good (Use is apparent, but not that much) condition, is the action on the engine cooling anode zinc taking the beating keeping the main hull zincs active but not being aggressively ate up?

Happy to change out the engine anode zinc. cheap and easy to accomplish. saving money by having two seasons on the hull zincs is a big plus.
Incidentally, there is no action on the wheel to show any lack of zinc protection. still a bright finish with no indication of electroless to the blades.

Comments?

Thanks, Al-Ketchikan
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Old 09-19-2017, 11:30 PM   #2
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Sounds all good, and the regular change of the engine zinc's could be influencing the vessels zinc wastage (Galvanic and stray current corrosion),

Just to note the following and general Zinc Advice:

1) Not all Zinc's are created equal some are alloyed with Magnesium/Aluminium
2) The first property to consider is their electrical potential. All metals generate a negative voltage (as compared to a reference electrode) when immersed in water. The lower – the more negative - the voltage, the more active the metal is considered to be, for example:

A) Magnesium generates -1.6 Volts, i.e. negative 1.6 volts.
B) Aluminum sacrificial anode alloy generates -1.1 Volts
C) Zinc, -1.05 Volts

3)In order to provide protection, the highest practicable voltage difference possible is required between the sacrificial anode and the metal to be protected.
For example, if zinc is used to protect a bronze propeller, a “driving or protecting voltage” of negative –0.75 volts will be available, i.e. zinc at -1.05 volts minus bronze at -0.3 = - 0.75 volts.

If aluminum anodes are used this increases to -0.8 Volts.

Magnesium anodes increase this to -1.3 volts.

The bigger the difference in voltage, the more protection you get. But, beware, some materials (aluminum) can be “overprotected”

4) The second property that is important is the current capacity of the anode material. The anode generates a voltage difference and this drives a current between the anode and the protected metal and through the water. It’s like having a bigger battery, the more capacity you have the longer it will keep protecting. Incidentally, for a particular anode, the rate of current flow is dependent on the surface area of the anode and the longevity depends on the mass. For the same size anode the relative capacities are:

A) Zinc: 100 (Taken as a datum e.g. this could be 100 days)
B) Magnesium: 30
C) Aluminum anode: 130 – 150 (Different manufacturers quote different ranges)

5) So if you used a magnesium anode in place of the “100 day” zinc anode it would only last 30 days.

6) The aluminum anode would last between 130 and 150 days.

7) NOTE: The "Zinc Equivalent Weight" (ZEW). This is the amount of zinc that the aluminum anode is equivalent to in terms of capacity.

8) The third property is Quality of the Anode Alloy

9) A word of caution about the metals used !!

10) Not just any zinc or any aluminum will work. Beware ! There are some imported anodes which are of questionable quality. It is important to ensure that the anodes you buy are made to the appropriate military or marine specification. Installing cheap or sub-standard anodes will undoubtedly cause increased and potentially very expensive corrosion problems. The most common material specifications are:

A) Zinc: MIL-A-18001K
B) Aluminum: MIL-A-24779(SH)
C) Magnesium: MIL-A-21412

Cheers Steve
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Old 09-20-2017, 01:03 AM   #3
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Sounds all good, and the regular change of the engine zinc's could be influencing the vessels zinc wastage (Galvanic and stray current corrosion),

Just to note the following and general Zinc Advice:

1) Not all Zinc's are created equal some are alloyed with Magnesium/Aluminium
2) The first property to consider is their electrical potential. All metals generate a negative voltage (as compared to a reference electrode) when immersed in water. The lower – the more negative - the voltage, the more active the metal is considered to be, for example:

A) Magnesium generates -1.6 Volts, i.e. negative 1.6 volts.
B) Aluminum sacrificial anode alloy generates -1.1 Volts
C) Zinc, -1.05 Volts

3)In order to provide protection, the highest practicable voltage difference possible is required between the sacrificial anode and the metal to be protected.
For example, if zinc is used to protect a bronze propeller, a “driving or protecting voltage” of negative –0.75 volts will be available, i.e. zinc at -1.05 volts minus bronze at -0.3 = - 0.75 volts.

If aluminum anodes are used this increases to -0.8 Volts.

Magnesium anodes increase this to -1.3 volts.

The bigger the difference in voltage, the more protection you get. But, beware, some materials (aluminum) can be “overprotected”

4) The second property that is important is the current capacity of the anode material. The anode generates a voltage difference and this drives a current between the anode and the protected metal and through the water. It’s like having a bigger battery, the more capacity you have the longer it will keep protecting. Incidentally, for a particular anode, the rate of current flow is dependent on the surface area of the anode and the longevity depends on the mass. For the same size anode the relative capacities are:

A) Zinc: 100 (Taken as a datum e.g. this could be 100 days)
B) Magnesium: 30
C) Aluminum anode: 130 – 150 (Different manufacturers quote different ranges)

5) So if you used a magnesium anode in place of the “100 day” zinc anode it would only last 30 days.

6) The aluminum anode would last between 130 and 150 days.

7) NOTE: The "Zinc Equivalent Weight" (ZEW). This is the amount of zinc that the aluminum anode is equivalent to in terms of capacity.

8) The third property is Quality of the Anode Alloy

9) A word of caution about the metals used !!

10) Not just any zinc or any aluminum will work. Beware ! There are some imported anodes which are of questionable quality. It is important to ensure that the anodes you buy are made to the appropriate military or marine specification. Installing cheap or sub-standard anodes will undoubtedly cause increased and potentially very expensive corrosion problems. The most common material specifications are:

A) Zinc: MIL-A-18001K
B) Aluminum: MIL-A-24779(SH)
C) Magnesium: MIL-A-21412

Cheers Steve
Wow Steve, what a report! I am amazed at the techical assistance that flows in this forum. Bottom line Steve, is I use the zincs from the same boat yard each year and as to where he purchases inventory I doubt any of this information is involved in the purchase. Sad to say but the only data on the zinc anodes is the inventory number and price!! But as indicated, the change schedule is now established at five months. I am hopeful your observation that this engine anode zinc is the first line sacrifice is good a place as any to use as a change agent.
Thanks for the lesson.
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Old 09-20-2017, 03:34 AM   #4
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Believe in annual inspection and, as needed replacement.
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Old 09-20-2017, 08:46 AM   #5
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Internal engine zincs do not do anything to limit corrosion on external parts like props, rudders and thru hulls. And vice versa.

What may have changed in the last year is that an adjacent boat with a D.C. fault to the bilge water or on the shore power ground has moved or has fixed his problem.

David
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Old 09-20-2017, 09:09 AM   #6
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If I had a boat and found the zincs not wasting away like normal, I would first check the grounding between the zincs and the vessel ground. Electricity takes the path of least resistance.
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Old 09-20-2017, 09:55 AM   #7
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Al, stubones advice is a good as well. I found that the steel mounting straps of the zincs on my keel were not bonding well to the steel keel. Pulled them all off, wire brush and chisel work to get back to bare metal. Bolted them back on making sure I had metal to metal contact.

The clues were: 1) shaft zinc burned up first; 2) marine growth on the keel zincs.

I think if the zincs had been bonded to the keel better, they wouldn't be a happy home for barnys and the like. Put 2 zincs on the shaft this spring, will find out if I'm right next spring!
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Old 09-20-2017, 10:14 AM   #8
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The only way to truly know is to use a reference anode and an electrical meter. It will tell you everything you need to know. If you cannot or do not understand how, Hire someone for a corrosion survey.
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Old 09-20-2017, 11:39 AM   #9
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Al, stubones advice is a good as well. I found that the steel mounting straps of the zincs on my keel were not bonding well to the steel keel. Pulled them all off, wire brush and chisel work to get back to bare metal. Bolted them back on making sure I had metal to metal contact.

The clues were: 1) shaft zinc burned up first; 2) marine growth on the keel zincs.

I think if the zincs had been bonded to the keel better, they wouldn't be a happy home for barnys and the like. Put 2 zincs on the shaft this spring, will find out if I'm right next spring!

As often the case, asking to be advised of the spring results is a reach as humans tend to forget intended efforts in that space of time. Yes, your observation may have cause, the shaft zinc while in extreme use, still was in a reasonable shape, yet it obviously was the first strike for destruction. In reflection, all the other zincs were clean in terms of marine growth.

As to actions by near by boats, it is hard to judge. I do keep an eye on immediate boats to assure the power cords are out of the water anything more is speculation. Said as there is no visual or verbal information to judge conditons current from past.

It will take next years pull to ascertain if this zinc retainment is a fluke or conditions in our harbor have changed for the better.

Thanks for the comments.

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Old 09-20-2017, 01:00 PM   #10
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I always confirm a solid connection between zinc's and the item they are attached to.
Just bolting them on does not ensure a good connection.
Metal surfaces, zinc and base metal, must be clean. Sanded thoroughly.
I then check each zinc with my ohmmeter for approx. 0.1 to 0.2 ohms. If not then I go at it again.
Zinc oxidizes from air / moisture contact and the oxide can interfere even when not heavy enough to be easy visible so zinc anode mounting surfaces also need to be cleaned.
I have had to redo the mountings several times to get that low resistance reading.

Much more and the zinc's are not connected well enough.

I suggest those ohm readings as most meters cannot reliably read less and often probes themselves contribute enough that the meter will not read less.
There are better meters but they are not needed except for much more specialized application and are EXPENSIVE.
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Old 09-20-2017, 01:20 PM   #11
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The 1 ohm/resistance test needs to be conducted OUT of the water for reliable results. In water the reference anode test is needed.
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Old 09-20-2017, 05:37 PM   #12
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You could put a coat of No-Ox-Id A grease on the mounting patch, bolts and back of the zinc to assure a good electrical connection. I'm not it wold last a year underwater, when put on a shaft zinc, but would likely still be there a year later on hull zincs.

Electrical Contact Lubricant - Conductive Electrical Grease | Sanchem, Inc.
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Old 09-20-2017, 07:44 PM   #13
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If I had a boat and found the zincs not wasting away like normal, I would first check the grounding between the zincs and the vessel ground. Electricity takes the path of least resistance.
I vote for this one.
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Old 09-20-2017, 09:28 PM   #14
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Originally Posted by djmarchand View Post
Internal engine zincs do not do anything to limit corrosion on external parts like props, rudders and thru hulls. And vice versa.

What may have changed in the last year is that an adjacent boat with a D.C. fault to the bilge water or on the shore power ground has moved or has fixed his problem.

David

Dave's first paragraph confirms what I have always understood to be the case. Furthermore, since those two electrical systems are separate, it doesn't matter that the anodes are different between the engine and boat.

Dave's second paragraph also seems to make perfect sense to me. Our boats are influenced by the environment around us, and very few of us keep our boats in an unchanging environment.

I check the engine zincs every 3 months. The boat zincs get checked by a diver every three months and are changed when the diver thinks they are down 50%. Currently, my boat is on the hard and I am changing all the zincs. It is cheaper to have the yard change the zincs (unfortunately, I can't remove the old zincs on the hard due to yard restrictions) than it is having the diver do it.
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Old 09-20-2017, 09:41 PM   #15
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Al

Best luck keeping your anodes and diodes as kissen cousins... sounds a littler sexier don't it!

Great that you started this thread. Lots of great info I copied and placed in my Anode folder!

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Old 09-20-2017, 10:18 PM   #16
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Al

Best luck keeping your anodes and diodes as kissen cousins... sounds a littler sexier don't it!

Great that you started this thread. Lots of great info I copied and placed in my Anode folder!

Well, the conversations took a fearful turn to technical but I asked for that!!
Here I am thinking what a good deal I have with two years on the zincs. What confuses me the most is the hull (fiberglass) in reality, was clean enough that a light pressure wash would have me with a second year on the copper (Sorry, can't say that anymore) 'bottom' paint. The yard had to make some profit other than a haul fee so paint it was. Anyway Art, it is done and we will take a peek next fall and report results and conditions.
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