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Old 02-27-2017, 12:45 PM   #1
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Got to the rudder zincs just in time



You can see my shaft zincs sitting right next to it in this picture.

Just had diver a week ago said "40%"..

Good excuse to put on the scuba gear.
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Old 02-27-2017, 07:49 PM   #2
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Yikes. Hopefully they haven't been gone long. Might want to use a different diver next time.

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Old 02-27-2017, 07:51 PM   #3
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To be fair, they were around 90 days old which is about right for the area I had it docked, and we just travelled 400 miles down the intercoastal in a week *after* the diver did the bottom. just glad I poked my head under the boat today.
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Old 02-27-2017, 07:59 PM   #4
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I barely got to my engine zincs in time. No excuse really. 3 annodes, 2 in the after cooler and one in the heat exchanger. The lower aftercooler was down to 25% and fell apart as I removed it. The other two were OK.
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Old 02-27-2017, 10:31 PM   #5
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I barely got to my engine zincs in time. No excuse really. 3 annodes, 2 in the after cooler and one in the heat exchanger. The lower aftercooler was down to 25% and fell apart as I removed it. The other two were OK.
That's one of the upsides I suppose of being trapped above the first dam on the Missouri River and the boats come out six months of every year - our zincs last for years, even when we do magnesium.
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Old 02-28-2017, 12:07 AM   #6
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Put a giant zinc ( or better yet, aluminum) anode on your transom and bond everything to it with shaft brushes etc. Then the rest of the zincs are not as critical.
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Old 03-02-2017, 12:34 PM   #7
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Just had diver a week ago said "40%"..
It has always been my understanding that zincs should be replaced at around 50%. You were already beyond the duty cycle when you were advised by the diver.

If you're at 90 days, then IMHO you are under zinc'd and should consider increasing surface area of zinc. If this is on shafts, then add more or larger. If this is on a rudder, go up a size or two.
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Old 03-02-2017, 01:04 PM   #8
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Believe its 50% weight and not visible remains.

Not easy to check so 50 % visible may even be a little late so fudge up.
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Old 03-02-2017, 04:12 PM   #9
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Put a giant zinc ( or better yet, aluminum) anode on your transom and bond everything to it with shaft brushes etc. Then the rest of the zincs are not as critical.

Hmm.. so all of my stuff is bonded and I do have a giant transom zinc. Although my shafts are not... I actually went through and rebonded about half of the boat a couple months ago because there was some resistance between the rudders. I do have good continuity from shaft to rest of boat tho, guess through transmission.
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Old 03-05-2017, 02:26 AM   #10
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Believe its 50% weight and not visible remains.
50% surface area.
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Old 03-05-2017, 05:25 AM   #11
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*Periodically inspect your zincs, and when they have corroded to under 50% their original weight they should be replaced.* To lengthen the replacement interval, increase the weight of zincs used.

Above is from.....

BoatZincs.com (978-841-9978) - FAQs

Though surface area is the real measure of available protection and pretty much all you can go by when looking at them...

But I have seen some zincs that looked like new till you looked closely and saw how porous they looked and how light they were.

So I guess weight is important but surface area is more practical.
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Old 03-05-2017, 09:50 AM   #12
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From Nigel Warren's "Metal Corrosion In Boats":

The protection (provided by the anode)... depends on the exposed area of the anode and its efficiency.
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Old 03-05-2017, 10:32 AM   #13
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easy to weight them if you really want using a short ruler, a fulcrum and the new and old zinc.

Put the old zinc at the end of the ruler, fulcrum in middle and move the new zinc from the end toward the fulcrum. The percent of distance the new zinc, at balance, from the fulcrum is the % of metal left in the old zinc.

yup too mich time on my hands today.[]
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Old 03-05-2017, 10:52 AM   #14
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True, but taking them off underwater and finding out they still have months left seems a bit silly....


The surface area is probably the best indicator...but I cant say for sure as I have seen zincs look nearly full size but up close like a sponge for texture.
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Old 03-05-2017, 11:12 AM   #15
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At my company, we use three criteria to determine whether or not to replace an anode:

1.- Is it less than 50% depleted? (based on overall remaining size)
2.- Are the attachment screw threads still completely covered by anode material?
3.- Are we confident the anode will still be providing protection until our next service?

If any of these conditions are not met, we replace the anode.
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Old 03-05-2017, 11:17 AM   #16
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At my company, we use three criteria to determine whether or not to replace an anode:

1.- Is it less than 50% depleted? (based on overall remaining size)
2.- Are the attachment screw threads still completely covered by anode material?
3.- Are we confident the anode will still be providing protection until our next service?

If any of these conditions are not met, we replace the anode.
That pretty much sounds like what my diver does as well. At least what his guys do. I am not sure that he is doing much diving himself these days but managing the business. I just want to be sure that my boat is protected. Since it only gets inspected every 3 months, my zincs are probably replaced q 9 months on average.
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Old 03-05-2017, 01:32 PM   #17
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But I have seen some zincs that looked like new till you looked closely and saw how porous they looked and how light they were.

So I guess weight is important but surface area is more practical.
A porous or pitted zinc would have more surface area than a solid one, but less mass.

So which is it?

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Old 03-05-2017, 02:30 PM   #18
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A porous or pitted zinc would have more surface area than a solid one, but less mass.

So which is it?

��
I wish I knew...

I change by gut....worked for me but have been looking at zincs for 50+ years.

The experts, if you can call them that, say weight of zinc involves longevity....the surface area involves ability to protect (ongoing).

Fstbottoms makes a lot of sense in there are several factors when to replace...just depends on you betteing how much anode is left in the alloy you have bolted or welded on and its ability to protect.

If you figure out the right answer...I am all ears....
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Old 03-05-2017, 03:22 PM   #19
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I wish I knew...

I change by gut....worked for me but have been looking at zincs for 50+ years.

The experts, if you can call them that, say weight of zinc involves longevity....the surface area involves ability to protect (ongoing).

Fstbottoms makes a lot of sense in there are several factors when to replace...just depends on you betteing how much anode is left in the alloy you have bolted or welded on and its ability to protect.

If you figure out the right answer...I am all ears....
Just messing with you.

But I hope no TFer runs out of air due to analysis- paralysis while diving on their anodes.

Once I make a decision to change mine, I do. If they look better or worse than the last periodicity, adjust accordingly for next time.

I check mine with a borescope from the dock.
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Old 03-05-2017, 03:35 PM   #20
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Just messing with you.

But I hope no TFer runs out of air due to analysis- paralysis while diving on their anodes.

Once I make a decision to change mine, I do. If they look better or worse than the last periodicity, adjust accordingly for next time.

I check mine with a borescope from the dock.
Good - Lot less danger than diving at the dock having possible stray electrical current. With as many times and different areas they go in...I wonder why pro divers at docks do not get bothered/electrocuted from stray current?? Maybe some do.
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