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Old 15-07-2007, 05:40   #1
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Putting New Zincs on a Steel Boat - How to do it?

The boat I'm looking to buy right now has no zincs, since it's in the fresh water. It's a steel boat.

I need to add a full compliment of zincs to the boat to prepare it for salt water. It's a steel hull.

How does one go about this? I often see zincs on rudders, keels and of course on the main part of the hull. The main part of the hull makes sense to me - drill hole, use backing plate and bolt on, bedding with 5200 from the inside to keep water out.

The rudder and keel attached zincs aren't so clear to me. Do you drill holes and then tap threads into those holes to hold the annodes in place?

Anyone have any tips for doing this project?

For those following the story, we are looking at buying our junker now, before our Gulfstar Hirsh sells so we can move off the boat and have it ready for showings at all times. A little more expense, but maybe a LOT less headache.
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Old 15-07-2007, 08:58   #2
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On the commercial boat on which I was the Engineer, all the zincs were cast with tabs which were welded on. Replacing, they were cut off, ground, and new ones welded on. There was a lot of zinc, around 250 lbs of it on a 106 ft, 160 gross-tons hull. You really want to consult a steel boat builder to determine how much zinc you'll need. You might also get useful information from some of the zinc manufacturers, Sea-Shield, Reliance, Canada Metals, others. Also check out the electronic protection systems at Electro-Guard, corrosion and cathodic protection specialists for boats, yachts and small ships. . These units get more and more attractive as the price of metals, including zinc, goes up.
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Old 15-07-2007, 15:37   #3
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Quote:
Originally Posted by EngNate
On the commercial boat on which I was the Engineer, all the zincs were cast with tabs which were welded on. Replacing, they were cut off, ground, and new ones welded on. There was a lot of zinc, around 250 lbs of it on a 106 ft, 160 gross-tons hull. You really want to consult a steel boat builder to determine how much zinc you'll need. You might also get useful information from some of the zinc manufacturers, Sea-Shield, Reliance, Canada Metals, others. Also check out the electronic protection systems at Electro-Guard, corrosion and cathodic protection specialists for boats, yachts and small ships. . These units get more and more attractive as the price of metals, including zinc, goes up.
Great idea about the cathodic protection system, Nate! I wasn't even thinking that way. Thanks.

I'm checking into it now for the planned boat. You're right about the increasing cost of the metals. Although this unit is bound to up my power budget a little bit, it seems like it will save $$ in the long run over the (extended) life of the hull.

Thanks
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Old 15-07-2007, 17:25   #4
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Sean-
I think I'd just get some compatible 1/4x20 studs, drill holes in the hull, weld 'em in nice and tight with a backing plate, and then be able to bolt on the zincs with a conventional drill hole and nut. (Maybe a Nylock?)

No welding needed after the initial mounts.
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Old 15-07-2007, 18:04   #5
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Our steelie has ss bolts welded head-first onto the hull. To replace zincs its just a matter of drilling the new ones using the old ones as templates, then fastening them on with nyloc nuts. The rudder had nuts and screws through the rudder and zincs on either side, but I replaced them with threaded ss rod with nuts either side of the rudder, so now replacing rudder zincs is the same as the hull ones. It all seems to work ok.
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Old 15-07-2007, 18:54   #6
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Then again...Sean, why not just plasma spray the hull with zinc?<G>
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Old 15-07-2007, 21:07   #7
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Well connected...

I have been told that it is wise to check that there is a good electrical connection between the steel of the hull and the zinc.
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Old 16-07-2007, 01:33   #8
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The reason for welding the annodes on is to assure that the electrical connection remains good for the whole life of it. As the zinc diasapears it may become loose on a stud or bolt and the connection suffer. No continuity no protection.......no ..... The prop should be protected with the right size shaft annode bolted on. A recent method done and proven (three Years) by one of our members (metal boat society) was to weld stainless steel blocks onto the hull, and then weld stainless studs to that. This allowed the annode to stay in touch with the hull, because the stainless bits dont need to be painted. The annodes should also stand off from the hull. The direct contact with anti foul can cause problems.
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Old 11-08-2007, 17:51   #9
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Weld them on , or if bolted use a small tack on on one corner to guarantee a good connection. Corroision arond bolts can insulate them and let you boat corrode badly.
Brent
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Old 11-08-2007, 19:47   #10
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on my old steel boat i tack welded the bolts to the outside of the hull that way there is no hole through the hull and if for some reason a bolt gets dammaged it is easier to replace. And if you hit a log or something and it hits your annode it will break off with no hole left in your hull. i never had one come off the hull anyway.
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