Currently in a haul out to fix some serious over zinc damage around the shaft log and

Currently in a haul out to fix some serious over zinc damage around the shaft log and am stuck on how to move on from here. There is an original steel piece that spanned the rib gap where the shaft goes by. It is rusted beyond rust and at the ends where the bolts are the wood is quite wasted away. I am thinking of removing the steel and getting the yard to fabricate a new one from stainless? It may require a two piece design as the original
was put in before planks went on. Wood repairs wise , dig out and CPS hole and fill with epoxy or wood patch? If I can sister with stainless then hopefully that will go up far enough to good rib. To other wood boat owners reading this , this is what happens when previous owners tie all the fittings in a well intentioned but flawed bonding system in wood. We didn’t find this until we noticed water appearing from under the genset area and removed the genset , fortunately a slow weeping! Thanks for any ideas, I’ll post the final fix.

I agree with over bonding. What do you consider over zinc. If possible pictures of the zincs to get an idea is it too many, if so how many too much.
That wood almost looks like not original as the stringer does not appear to be affected.

My shafts are isolated from trans/engine and nothing is bonded to zinc on transom except the shafts with shaft brushes. The rudders have their own zinc. Haul out in two weeks.

Here is a picture of what was on the boat when we got it, there were two large plate zincs and a rudder and prop spinner.


I would be interested in how your shaft is isolated, ours is just a straight metal to metal plate. Given that the rudder is bronze and so is the bracket holding it I am not sure why it even has a zinc, there are no dissimilar metals to form an anode / cathode combination, thoughts?

Marinex said:

Here is a picture of what was on the boat when we got it, there were two large plate zincs and a rudder and prop spinner.


I would be interested in how your shaft is isolated, ours is just a straight metal to metal plate. Given that the rudder is bronze and so is the bracket holding it I am not sure why it even has a zinc, there are no dissimilar metals to form an anode / cathode combination, thoughts?

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The rudder shaft is stainless. I have drivesaver between trans coupler and shaft coupler. It is non metallic.

I have one brick size transom mount and two shafts. I can see some excess on yours. Even mine I was told was too much, I will see in a few weeks.

I had the Electro-Guard system with its ever-visible meter to let me know how the bonding and zinc situation was playing out on my woodie GB. Never used shaft zincs; never used zincs on bronze rudders. Just the sacrificial and ref zincs on either side of the bottom about a foot or two in from the transom. ALL through-hulls, tanks, engines, shafts, etc thoroughly and completely bonded. Never and issue in 29 years. Without as system monitor, you are playing Russian roulette.

Here is my brick, then two on each shaft, one each on rudders

rgano said:

I had the Electro-Guard system with its ever-visible meter to let me know how the bonding and zinc situation was playing out on my woodie GB. Never used shaft zincs; never used zincs on bronze rudders. Just the sacrificial and ref zincs on either side of the bottom about a foot or two in from the transom. ALL through-hulls, tanks, engines, shafts, etc thoroughly and completely bonded. Never and issue in 29 years. Without as system monitor, you are playing Russian roulette.

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Rich, The rudder zinc are optional, as are the shaft zinc.
I replaced all thru hulls when I got the boat after survey identified wood electrolysis, which was cut out and repaired. The guys doing the work and I agreed no bonding to thru hulls. They wanted to talk me out of transom zinc. I said let me see for myself.
The rudder zinc is a precaution and they are not bonded.
I will let you know what they look like in a few weeks. (I can see the transom zinc is still viable.

Wood boats, over zincing can be an issue, glass boats all I have ever heard is copper bottom paint burning.

I replaced the thru hulls when we got the boat ten years ago as they were original and some were frozen, also some fuzz around each. We left them isolated and unbonded and have had not an issue at all since then. If a system is fully bonded as Nigel Calder says "in perfect condition" and monitored then you probably would be okay. But if a bonding system is installed and not balanced to the total zinc amounts then the sacrificial link becomes your wood boat. In our case under the genset and hidden, fortunately we caught it before really serious wood issues arrived.

Marinex said:

I replaced the thru hulls when we got the boat ten years ago as they were original and some were frozen, also some fuzz around each. We left them isolated and unbonded and have had not an issue at all since then. If a system is fully bonded as Nigel Calder says "in perfect condition" and monitored then you probably would be okay. But if a bonding system is installed and not balanced to the total zinc amounts then the sacrificial link becomes your wood boat. In our case under the genset and hidden, fortunately we caught it before really serious wood issues arrived.

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My Electro-Guard had a rheostat to let me adjust as necessary to keep the meter in the green as zincs/bottom paint aged. Yes, the copper-laden paint is involved too. Ref zinc rarely replaced, and the sacrificial about every year. That big plate I see in a photo above was twice as big as my Electro-Guard would stand. I put one like that on one time and the meter pegged until after several cuts, it was half that size (42 foot boat). I do not see why it seems to be a hard thing to ensure the bonding is in good shape. I managed with 11 thru-hulls, twin shafts/rudders, four fuel and two water tanks. I took a crawl through the bilges once every year to make sure it was all shiny, and the E-G would let me know if something were askew. I moved in or left more than one transient marina when I pulled in to find the meter pegged due to marina dock issues.

Is there a write up about how exactly a GB should be bonded. I think my GB has a similar, though not quite as severe a problem. @Marinex or someone -could you explain the science behind this?

thx

mplangley said:

Is there a write up about how exactly a GB should be bonded. I think my GB has a similar, though not quite as severe a problem. @Marinex or someone -could you explain the science behind this?

thx

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The idea behind bonding is to link all the underwater metals, assuming they are all of similar nobility, so that they all corrode at the same rate rather than have a localized hotspot quickly destroy a fitting. The wooden boat over-zincing issue discussed here is a different animal altogether, but I think a properly bonded hull would experience less over-zincing damage to its wood than one without bonding.

When it comes to wood corrosive control bonding all metals and having a system installed where you can keep the levels right is probably the best ideal situation. Unfortunately not every owner is diligent about this and things get added and subtracted to the bonding loop or maintenance gets neglected and trouble begins. In boats other than wood this leads to metals getting eaten away, for instance your aluminum prop on your outboard when the zinc is used up. But the fibreglass hull is still okay.


On a wood boat when things get out of whack then the resulting electrochemical corrosion can start attacking the wood by destroying the wood fibres and turning them into sawdust.


I believe as others have said that unbonding, while not ideal perhaps, does take a long time for any harm to come to the unbonded through hulls, many decades in fact.


As one old wood sage put it, I can afford a new through hull every fifty years but not a new wood hull every five.

This is some excellent reading on the subject as well:


https://waitematawoodys.com/2018/11...cal-deterioration-in-a-wooden-boat-look-like/

We have unbonded through-hulls on LilyD, never had any hydrolysis fuzz there. We have a Monel shaft, bronze prop and a steel rudder, and use one shaft zinc and one rudder pancake zinc. There were two shaft zincs when we got the boat but some hydrolysis fuzz at the stuffing box, so we cut back to one shaft zinc and it was better, although still needs vinegar spray now and then. We have no zincs on the hull.
We did try going with no shaft zinc but that was the year we developed a leaking bilge pump switch and the prop started to "pink". I put the shaft zinc back on, better a bit of fuzz than losing a prop.

Jim

The shaft log wood is now replaced with a purple heart filler piece. The original piece is shown here and at 54 years its warranty was up. In the end we had some water leakage due to wood wasting by the galvanic action of the over zinc, and some was the gasket material used had failed. The gasket material was a canvas fabric and some sort of adhesive of the day, maybe just painted canvas.


We had to mill the purple heart shim down to the original thickness of 1/2 inch roughly and then using a router and a scarf cutting jig to make it taper to approx. 1/4 inch at the stern end. If you have to do this the taper width is fairly critical in that the shaft has to sit centered in the stern tube, the important part of this adjustment is to measure the shaft at the top cutlass bearing and account for any loss there. Ours had 54 years of wear so we had to increase the taper to get our worn area centered in the tube.


We replaced the rusted out metal cross piece with a three piece stainless part bolted together after cleaning out and epoxying the wood damage done the rib. I used tubing and a nylon washer to isolate the one 3' bronze bolt that goes all the way down into the keel.



I can answer any questions for those who may go down this road!

Marinex, that is one nice craftmanship you have shown there.

I see the part replaced, what about the plank underneath, was that not affected?

The underlying keel planking was unscathed, not sure of the wood type but you could hit it with a hammer and not leave a dent, extremely dense. I was very happy to see that it was intact. Here are a couple more before and after pictures of the cleanup.

The hull is Philippine mahogany from what I have read and ribs are Yacal

So if the hull plank is not affected could the shaft log have been a lesser wood I wonder.