Do I need zincs?

[Hard A Lee]

I'm going to be putting an S2 6.8 in the Great Salt Lake this summer. It has a shoal keel with a centerboard. Do I need to add any kind of zinc to the centerboard? The tiller is fiberglass I believe. I think the centerboard is cast iron and the pivot pin is stainless.

[reefhunter]

Yes, I would put one on the either side of the rudder and one on the prop strut

[Mark1977]

Yes, any metal under the water should have a zink attached to it.

[No Salt]

Magnesium is preferred for fresh water. Zinc is for salt water.

[reefhunter]

Originally Posted by No Salt

Magnesium is preferred for fresh water. Zinc is for salt water.

FYI - the Great Salt Lake is saltwater, not fresh

[fstbttms]

Originally Posted by Hard A Lee

I'm going to be putting an S2 6.8 in the Great Salt Lake this summer. It has a shoal keel with a centerboard. Do I need to add any kind of zinc to the centerboard? The tiller is fiberglass I believe. I think the centerboard is cast iron and the pivot pin is stainless.

The answer is no, you probably do not need to put a zinc on your centerboard.

1.- The centerboard is likely well-isolated from source of onboard stray current.

2.- The centerboard is likely too large a piece of metal to be adequately protected by a relatively small rudderplate or teardrop zinc.

Your iron centerboard may very well rust, but a zinc is not going to remedy this.

[No Salt]

Originally Posted by reefhunter

FYI - the Great Salt Lake is saltwater, not fresh

Woops, my bad. I read "Great Lakes" rather than "Great Salt Lake".

[Hard A Lee]

Thanks fstbttms

I think it is a little rusty and I didn't know if that zincs would help with that at all or not...Been having some trouble with it lowering and I was wondering if that had anything to do with it as well...

[Mikerodrig27]

I'd stick a zinc on the centerboard. I wouldn't be concerned with the onboard stray current so much as I would be concerned with the galvanic corrosion. With the centerboard being cast iron and the Salt water having tested pH levels as low as 7.5, I'd be concerned that watar is going to be a very good electrolyte. Also the salinity is sometimes higher than the ocean which isn't a plus.

[Andrew Troup]

I'm not sure how much a single zinc would help, and as has been said a cast iron board will rust regardless of galvanic issues. (Although probably not as much as steel would, but if concerned, refer end of post for an alternative treatment)

I would be seriously concerned, however, about your stainless pivot pin, not because of galvanic issues (the cast iron will protect it) but from contamination corrosion.

Stainless steel, in contact with steel or iron, is prone to this, which many sailor are familiar with as a superficial problem, but what is less well known is that the resulting patches become 'active', at which point the passive parts of the same item go on the attack, and the pin literally consumes itself.

The reason is that the "passive" condition, which is responsible for the corrosion resistance which gives stainless steel its name, is maintained by an extraordinarily thin layer of oxide. It's hard to quantify, but it's of the atomic order, some say one tenth of one millionth of an inch thick.

And that's why stainless performs best when highly polished and kept clean.

Ferrous contamination destroys the film locally and permanently, until it is chemically removed, re-passivating the surface.

I would personally look at drilling out and bushing your centre-plate with Micarta (or Tufnol, or a tough reinforced thermoplastic, like nylon) and re-passivating, or replacing, the pivot pin.

(To enlarge the hole in your plate : if it's too large to get under a drill press, you might be able to borrow a 'magnetic base' drill)

- - - -

I would consider getting the cast iron plate zinc-sprayed, or aluminium sprayed (or fancier yet, the latter under the former) or hot-dip galvanised.

Inorganic zinc (a form of paint) is cheaper and might be just as good as hot zinc spraying (but nothing matches galvanising. Most people don't realise cast iron is suitable for this, BTW, but the galvanisers SHOULD know - don't count on it, however ...)

Hot metal spraying, while theoretically better, I've found, can be highly variable in durability, unless it's done by really good and highly informed operators with excellent quality control procedures)

If you decide against treating the whole plate I would certainly treat the hole for the bush, otherwise over time the bush will be tighten against the pin because rust occupies more space than iron.

Having bought a can of "cold galv" paint to do this, you might as well use the rest on the balance of the plate!

(To enlarge the hole in your plate : if it's too large to get under a drill press, you might be able to borrow a 'magnetic base' drill)

[Hard A Lee]

Thanks for the reply. I wondered about that stainless pin in there. The big problem will be dropping the centerboard. I wonder if the rust against the pin us what has been giving us problems with it not wanting to lower. In the past we've been able to crawl underneath when it's in the trailer and snake a loop of wire up there to give it a tug. Then it comes down. Not really a long-term solution. Especially since it will be in a slip. I'd hate to have to dive underneath every time we go out.

I so have access to a mag-drill and know of some places that do galvenizing. Or some cold galvy might be good enough!

[Sand crab]

I wonder if the high salinity content would affect corrosion. The lake varies from 5% to 27% salt content depending on the lakes level. Ocean water is about 3.5% salt.

[Andrew Troup]

Originally Posted by Hard A Lee

Thanks for the reply. I wondered about that stainless pin in there. The big problem will be dropping the centerboard. I wonder if the rust against the pin us what has been giving us problems with it not wanting to lower. In the past we've been able to crawl underneath when it's in the trailer and snake a loop of wire up there to give it a tug. Then it comes down. Not really a long-term solution. Especially since it will be in a slip. I'd hate to have to dive underneath every time we go out.

I do have access to a mag-drill and know of some places that do galvenizing. Or some cold galvy might be good enough!

Do you know anyone who knows anyone who has an overhead crane at work?
One you could drive the trailer under, and rig slings fore and aft?

That's how I've dropped centreboards, worked a treat. Rig some temporary props and the board comes clear, Wheel the trailer out with the board on, muscle it off (or use an engine hoist if too heavy), wheel the trailer back under the boat ...

If the quoted figures for salinity are kosher, I would DEFINITELY go for real galv over cold.

Try to find a galvaniser who will grit-blast the board themselves, so it can go straight in the bath without risky pickling, and you won't have to slave away with a power wire brush to knock off the worst of the rust.