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Old 08-02-2011, 23:42   #31
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Originally Posted by fstbttms View Post
In that case, if hanging a zinc over the side gives you peace of mind, then you may as well do it.
In fact I am hanging over the side but I don't do it so much for peace of mind, I will do whatever works for my boat, And so much for alkalinity, wouldn't think that it would matter so much in harbor with the tide going in and out and a river current etc, or do I have the wrong understanding of alkalinity?
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Old 08-02-2011, 23:44   #32
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And so much for alkalinity, wouldn't think that it would matter so much in harbor with the tide going in and out and a river current etc, or do I have the wrong understanding of alkalinity?
Hey, I'm just telling you what I read in Nigel Warren. You need to talk to a chemist if you want more than that.

But I have seen many, many examples of over-zincing.
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Old 08-02-2011, 23:49   #33
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LOL, okay...I am glad to at least know that you can over-zinc a boat and I have a much better understanding about anodes and electrolysis than I did before I made this.
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Old 08-02-2011, 23:53   #34
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on the issue of overzincing...if you have too many zincs on the shaft or rudder control you mentioned possible bubbling on the anti foul paints...

what if the zinc were spread out.. one here, one there. but all connected/bonded???



how would you bond all the through hulls? bonding wire to a submerged zinc? or would it be connected to the motor zinc?
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Old 09-02-2011, 00:49   #35
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I've done it, too. I got stuck with the boat in a situation where I knew it was overdue, a diver confirmed that the old ones were 90 to 95% gone and I knew I couldn't get it hauled out for another two months, at the earliest. By the time I did get it hauled out, my saildrive zincs were totally gone, but there was no corrosion damage and everything was fine.

Besides, it can't hurt! (Unless you forget they are there before taking off.)

ID
Had exactly the same problem when I hauled out a month ago, the zinc on my saildrive leg had virtually all gone in 12 months.

This erosion appeared to have got worse since the installation of a s/s ropecutter. I contacted M G Duff (UK annode supplier) as I would like to try and extend the life of these saildrive zincs if possible.

Their advice was a hanging annode. I need to run a 4mm bonding strap from a bolt on the saildrive to a convenient connector in the lazarette, the hanging annode is then connected and deployed overboard as close as possible (adjecent to) the saildrive leg.

I will let you know in 12 months time if this theory works
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Old 09-02-2011, 01:58   #36
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the other day someone was telling me if the boat is slipped in a marina and someone shorepower cord was dipped into the water, that it increases the corrosion rates and eats up the zinc...

but this same guy also told me that the zinc on the drive shaft had a 'wire brush' just like an electricl motor brush to contact it while it was spinning...

it was a broker guy..
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Old 09-02-2011, 04:17   #37
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the other day someone was telling me if the boat is slipped in a marina and someone shorepower cord was dipped into the water, that it increases the corrosion rates and eats up the zinc.....
That is true enough. I watch a friend move his boat very quickly when it was moored alongside live aboard boats. Within weeks the zincs had gone and the aluminium outboard leg lost its paint finish and started pitting. Something terribly wrong in that marina with shore power supplies.

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but this same guy also told me that the zinc on the drive shaft had a 'wire brush' just like an electrical motor brush to contact it while it was spinning... it was a broker guy..
MG Duff have one of these device in their catalogue.

Product Catalogue - Marine Cathodic Protection - MGDUFF

Whilst owners may assume that the prop, P bracket and shaft are all nicely connected together the truth may be completely different and the only way to tell is to take the boat out of the water and measure the resistance between the various parts. Afterall most cutlass bearings have a rubber insert between the prop shaft and the P bracket. The connection between prop shaft and engine is via a gearbox full of oil.

Anodes that disappear in a year are doing their job, you should be more worried if they don't disappear because it means they are either oversized or not working.

The other likely area is that internal wiring connections between P bracket, shaft, Engine and battery neg are failing or not connected. I had to replace several cables here when the surveyor noted the high resistance reading between the under water parts and suspected the wiring, which turned out to be correct.

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Old 09-02-2011, 07:47   #38
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Old 09-02-2011, 08:31   #39
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the other day someone was telling me if the boat is slipped in a marina and someone shorepower cord was dipped into the water, that it increases the corrosion rates and eats up the zinc...
Unless there is a break in the insulation of the shorepower cord, I'd have to call this another dockside wive's tale. I see shorepower cords in the water every single day and have never noticed a correlation between that and rapid zinc depletion.
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Old 09-02-2011, 08:51   #40
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Fast Bottoms is correct. The sacrificial anode needs to be in the same electrolyte as the electrolyte which is creating the circuit between the anode and the cathode. The water outside the boat is a different electrolyte than the water inside the engine. This is exactly why engines have their own anodes for the block and heat exchanger and if you have one, the aftercooler.

It is DC current that causes electrolysis. A shorepower cord can become a pathway for DC current to flow but the AC in the same shore power cord is not the cause of electrolysis. If AC becomes partially rectified, that could be a problem.
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Old 09-02-2011, 12:40   #41
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ok, now i am the fool... shaft bonding/brushes exist... I woulda bet against that... but it does make sense, but just not 'feasible', so i discounted it...

i see that it is quite feasible... and that i will end up spending some time and money to get my boat surveyed for corrosion potential and get reccomendation to propery bond everything i can...


dang it... nothing can be easy... hehehehe.. just another thing to learn... and to think i was going to get into electrical engineering when iw as in high school and DVC
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