Zinc in fresh water ?

[edwardc]

Originally Posted by Laker

... My shaft is SS . I have very little exposed shaft. (Raised Catholic , very modest.) ...

Almost choked, I laughed so hard!

[sastanley]

Hanley, is that the highly prized "Dave Neptune prop"?

I can't imagine 2,500 RPM in gear with an A4!

[hanleyclifford]

That is indeed the Dave Neptune prop. 2500 rpm was easy so I know I have to get it repitched.

[Mo]

Hanley, while I was fixing the steering on my boat a couple of weeks ago I found another 3 bladed prop under my gas tank. Took it home to my garage and put the grinding wheel to it....can't see markings...any ideas where they should be except on the blade like my last one.

[sastanley]

Mo, I found mine on the hub face..like where the prop nut would contact it.

[67c&ccorv]

Originally Posted by Ball Racing

In salt water you use "zincs", fresh and brackish you use aluminum, and magnesium.
Right????

Correct - magnesium in fresh water.

Put two new ones on my rudder this season - don't have one on my Indigo prop and shaft as there is no room (I followed Tom's advice in the instructions);

...plus, I have a galvanic isolater in my electrical system.

[Mo]

Hanley,
I have part of that set up you have on my shaft. I've been using the bolt on anodes (the two halves). Mine has 7/8 shaft...what am I looking for to put one on the end like you have...part of something is on there already and there's a threaded hole in the end of it for the anode. Is there more to it than I'm seeing?

[hanleyclifford]

http://www.boatzincs.com/prop_nut_specs.html Check this out.

[tenders]

Originally Posted by Laker

Thanks , gang. My shaft is SS . I have very little exposed shaft. (Raised Catholic , very modest.)

I know the feeling--was raised Cathodic myself!

[ndutton]

Originally Posted by tenders

I know the feeling--was raised Cathodic myself!

Cathodic - Nice!

[hanleyclifford]

Originally Posted by tenders

I know the feeling--was raised Cathodic myself!

I think I was raised Anodic - I keep losing electrons (or is it marbles?).

[Mo]

Hanley,
Thanks for the link. I have the bronze piece on my boat so I just need to order the zinc. Didn't see one around here at any of the marine stores.

[Mo]

Shawn,
I found it right where you said it was. Put it on the bench grinder / brush side and it became quiet clear...it's a 13 / 7; A while back I talked to Hanley regarding the one currently on my boat...I think it's a 12 / 6 on the boat. I thought initially it was a 9 but probably read it upside down.

Thanks for the info..both of you guys. I like whats on there now but another option is always nice.

[hanleyclifford]

http://search.defender.com/search.as...opzinc&x=5&y=8 I like this catalogue and the company.

[jpian0923]

I hate to stir the pot but, can anyone comment on "In a marina you can hang zincs over the side. They don't have to be attached to your metal parts."

I struggled for an hour or more yesterday trying to get my prop on, without success. At the point that my feet and hands were "blue" and my fingers stopped working, I managed to find a diver that was just finishing up another job and I paid him $50 to put the prop on. He slipped away before I could ask him to put the zinc on.

I hate to lose that brand new Indigo to galvanic corrosion and I hate to think I have to get back into that 65 degree marina water again.

If hanging the zincs over the side will work, I'd rather do that.

Anyone?

[ndutton]

Originally Posted by jpian0923

I hate to stir the pot but, can anyone comment on "In a marina you can hang zincs over the side. They don't have to be attached to your metal parts."

Jim,

West sells exactly what you're looking for:
http://www.westmarine.com/webapp/wcs...classNum=10311
and contrary to the quote above, it needs to be bonded electrically to your underwater metals, particularly your prop shaft. Unless you have one of those flexible coupler things (I didn't see one in your pictures), connecting to your engine block will do fine, it's electrically continuous with the shaft. just clamp it on and drop the fish over the side.

It should buy you some time.

[ILikeRust]

There is a discussion of grounding and galvanic corrosion in Calder's massive tome, so I'll have to go back and dig into it again, but just for conversation's sake, should the engine be bonded to the raw water intake through-hull?

There is a small grounding lug bedded into the interior of my hull, right next to the raw water intake. I'm trying to remember, but I'm pretty sure there was a bonding wire from the engine to that little lug. I'm wondering if I should bond the engine either to that lug or to the through-hull - or maybe both. Or neither....

There just are too many things to know!

[ndutton]

Bill,

Unless the underwater metals are electrically bonded together they do not pick up protection from the sacrificial anode. That's the textbook version. Here are two real world experiences in contrast.

At the boat plants the only time we bonded the bronze thru-hulls together and then to the engine block was for the old high freq radio ground option listed in the brochure, otherwise never. I can't say whether this policy was for galvanic corrosion issues or if the mfrs were simply too cheap.

About three years ago I decided to bond my thru-hulls to the engine block to pick up anodic protection for them from my shaft zinc. Within a month the thru-hulls developed that white fur we sometimes see and one of the thru-hulls turned hot pink in color. This happened immediately after bonding, no other changes on board.

Out came the wire cutters and the bonding system went buh-bye. In my case I'm better off without the thru-hulls 'protected.'

This is one of the real attractions to plastic Marelon thru-hulls and valves.

[ILikeRust]

Yeah, I was kinda thinking it might actually be better for the through-hull to be isolated - no connection to the more "noble" metal. The prop shaft is stainless steel, and my new Indigo prop also is stainless - but the prop shaft key and the nuts holding the prop on are bronze. So I slapped the zinc back on the prop shaft, since I've got bronze directly in contact with stainless.

But I think that the bronze through-hull, which is several feet away from the prop shaft, not being connected to the prop shaft, should not be subject to galvanic corrosion. Also, it likely will end up being coated with ablative botom point.

I'll do a quick double-check of Calder's book to see what he has to say about it. The problem with his book is it's really too comprehensive for my simple boat. But there's a ton of good info in there - just have to wade through a lot of detailed technical stuff to get the few little nuggets that actually apply to my boat.

[sastanley]

+1 for marelon!

Bill T, I find the same with Nigel's books. Wow...way over my head on 90% of it..I just need the 'nuggets' for my boat too.

My step-father used the little fishy thing. His boat it self was never plugged into the dock, but he suspected the marina was a little 'hot' (nevermind the orange extension cord that went down into the neighbor's cabin.. )

As Neil noted, when you come into the dock, one of your added 'put away' procedures will need to be to clamp the fishy onto the prop shaft, or other engine part..like where the starter mounting bolt grounds to the block.. I wouldn't rely on the fact that you suspect a piece of bonding wire may actually be connected to the engine from somewhere else in the boat..might as well clamp right to the direct parts you want to protect..the engine/shaft/prop.

Just remove before you go sailing.

[jpian0923]

Thanks Neil. You saved me again.

[JOHN COOKSON]

For maximum protection the zinc and the shaft (or strut) need to be clean and bright when the zinc is installed. This assures good electrical contact.

I investigated a bonding system several years ago but never followed up on it.
Neil: I thought you were supposed to hang a zinc over the side connected by a wire to the bonding system??? Was this part of your set up?

TRUE GRIT

[hanleyclifford]

Neil did right by getting rid of that bonding system. On a fibreglass boat bonding is questionable: on a wooden boat it is deadly. Even on a fibreglass boat the collection of ions at the cathode could cause weakening of the hull material. That pink stuff is a warning. Best solution - bury thru hulls and seacocks in quality oil paint and replace them every thirty years. FWIW

[ndutton]

Originally Posted by JOHN COOKSON

Neil: I thought you were supposed to hang a zinc over the side connected by a wire to the bonding system??? Was this part of your set up?

I didn't use an over the side zinc. The idea of bonding the thru-hulls to the engine was to pick up anodic protection for them from the shaft zinc. It seemed prudent to me at the time but I'm a go with the flow guy and when I started seeing changes in the thru-hulls I yanked the bonding out in a matter of minutes. Let's not tempt fate while thinking we know better, yeah?

I referenced the grouper zinc for Jim because he specifically asked about such a system until he could restore his normal zinc.

[jpian0923]

Got it! And lunch too.

I'm thinking of running an engine ground wire to the stern locker to keep the Grouper Zinc in there, when not over the side. Seem feasible?