Zincs on fiberglass hull w/outboard, swing keel

[CloudDiver]

Main Sail, I wanted to ask your opinion on my Zinc Anode protection plan for a Catalina 22 swing keel (cast iron). The boat will be sailed exclusively in salt water and although I would prefer to sail it dry (for cost reasons), lets assume I will be in a slip or on a mooring ball.

Myself and a few other C-22 owners have recently completed or are in process of swing keel overhauls. I sand blasted, repaired, and completely epoxy encapsulated mine. So the idea of drilling and tapping the cast iron for mounting a zinc anode would compromise my water tight integrity and I just think that's nuts.
This suggestion came from Stingy Sailor and I plan on using it; I will drill a hole in the hull and epoxy in a stainless blind threaded bung ( I have several of these in 304 stainless 1/4"/20 and 5/16 that I use in custom chopper builds). I will weld a stainless tab to the back and drilled for a small screw. The bung will be glassed into the hull near the keel cable winch. The zinc will be bolted to hull bottom and the tab inside will have a wire that connects to the winch body (winch body is not painted, galvanized). The stainless keel cable goes down to the end of the keel and attached to the stainless eye bolt that threads about an inch into the cast iron. One poster pointed out that Blue Loctite or similar thread sealer will not inhibit conductivity enough to make all this useless.

When doing my research on galvanic corrosion I find most information is related to power boats or sailboats with inboards and little about smaller fiberglass sailboats with outboards. The few comments I have noted say if your keel is lead you don't have an issue anyway, and if your cast iron keel is completely epoxy encapsulated you are fine as well. But besides the keel (cast iron encapsulated or not), I have bronze keel hangers, bronze keel pin, stainless hanger bolts, stainless eyebolt and keel cable all below the water (as well as a bronze thru hull that is new, and the original 'volcano' tube that shows signs of galv corrosion).... Ergo, I think this is all worth protecting.

Does all this make sense or I am over-engineering it?

 

[Apex]

Attach a zinc to the outboard (Mine had a place on the cavitation plate) and another to the swing keel itself. I believe you want the protection bonded to what you are protecting, so a zinc on the hull provides no protection for anything.

 

[CloudDiver]

I think what you meant to say was " a zinc on the HULL won't protect anything". The intent of this suggested set-up is to avoid drilling and tapping a hole into the cast iron keel which I just put great effort into refurbishing and completely encapsulating in epoxy, save the threaded hole where the keel eye-bolt screws in. Also, the zinc is electrically connected to the keel via the keel cable.

Attach a zinc to the outboard (Mine had a place on the cavitation plate) and another to the swing keel itself. I believe you want the protection bonded to what you are protecting, so a zinc on the keel provides no protection for anything.

 

[CloudDiver]

This is the blind mounting bung with tang I made for attaching a zinc to the bottom of the hull. As Stingy Sailor suggested, the zinc will bolt in on the bottom of the hull just behind the keel, its pretty flat back there. In the bilge a wire will connect from the tang to the keel winch, electrically connecting the zinc to the keel cable, keel lifting eye, and the cast iron keel itself.
I basically need to bore a 3/4" hole and epoxy the bung in place, I'll use a small square of biax tape on the inside surface to strengthen it. The idea is that I could easily remove it by boring around it with a hole saw if it just plain doesn't work or the threads ever get mucked up. I have my reservations at this point simply because I don't think stainless is conductive enough for a good connection between the cast iron and that 6 feet of stainless cable. Thoughts?

 

[FourPoints]

My fear with that setup is putting that "bung" though your hull without a flange on the outside and nut on the inside to mechanically fasten it to the hull with adhesive sealant sandwiched between. With your intended design you will be relying 100% on the epoxy to stainless adhesive bond to ensure the water tight integrity of your hull, which I would be immensely uncomfortable with if that was my boat (or if I was even on board a boat with this in the hull).

As for the conductivity, I think it depends on how the cable is attached to the lifting bolt of the keel, but so long as that connection is electrically sound the rest of the idea seems fine to me.

 

[CloudDiver]

The overall diameter of the hole is 3/4". I would scuff the bung with coarse sand paper and clean with acetone before bonding, the bond will be very strong. On the inside of the hull I will lay down 2 or 3 glass patches on top and around the tang, maybe 3 x 3 inches. The idea of not using any kid of flange is that if I ever decided this wasn't working I'd be able to cut the bung out easily with a small hole saw going around it.

My fear with that setup is putting that "bung" though your hull without a flange on the outside and nut on the inside to mechanically fasten it to the hull with adhesive sealant sandwiched between. With your intended design you will be relying 100% on the epoxy to stainless adhesive bond to ensure the water tight integrity of your hull, which I would be immensely uncomfortable with if that was my boat (or if I was even on board a boat with this in the hull).

As for the conductivity, I think it depends on how the cable is attached to the lifting bolt of the keel, but so long as that connection is electrically sound the rest of the idea seems fine to me.

 

[monkeybars]

Main Sail, I wanted to ask your opinion on my Zinc Anode protection plan for a Catalina 22 swing keel (cast iron). The boat will be sailed exclusively in salt water and although I would prefer to sail it dry (for cost reasons), lets assume I will be in a slip or on a mooring ball.

Myself and a few other C-22 owners have recently completed or are in process of swing keel overhauls. I sand blasted, repaired, and completely epoxy encapsulated mine. So the idea of drilling and tapping the cast iron for mounting a zinc anode would compromise my water tight integrity and I just think that's nuts.
This suggestion came from Stingy Sailor and I plan on using it; I will drill a hole in the hull and epoxy in a stainless blind threaded bung ( I have several of these in 304 stainless 1/4"/20 and 5/16 that I use in custom chopper builds). I will weld a stainless tab to the back and drilled for a small screw. The bung will be glassed into the hull near the keel cable winch. The zinc will be bolted to hull bottom and the tab inside will have a wire that connects to the winch body (winch body is not painted, galvanized). The stainless keel cable goes down to the end of the keel and attached to the stainless eye bolt that threads about an inch into the cast iron. One poster pointed out that Blue Loctite or similar thread sealer will not inhibit conductivity enough to make all this useless.

When doing my research on galvanic corrosion I find most information is related to power boats or sailboats with inboards and little about smaller fiberglass sailboats with outboards. The few comments I have noted say if your keel is lead you don't have an issue anyway, and if your cast iron keel is completely epoxy encapsulated you are fine as well. But besides the keel (cast iron encapsulated or not), I have bronze keel hangers, bronze keel pin, stainless hanger bolts, stainless eyebolt and keel cable all below the water (as well as a bronze thru hull that is new, and the original 'volcano' tube that shows signs of galv corrosion).... Ergo, I think this is all worth protecting.

Does all this make sense or I am over-engineering it?

using anything out of 304 is a big mistake in salt water. 316 is much more durable

 

[FourPoints]

The overall diameter of the hole is 3/4". I would scuff the bung with coarse sand paper and clean with acetone before bonding, the bond will be very strong. On the inside of the hull I will lay down 2 or 3 glass patches on top and around the tang, maybe 3 x 3 inches. The idea of not using any kid of flange is that if I ever decided this wasn't working I'd be able to cut the bung out easily with a small hole saw going around it.

scuffed with coarse sand paper and acetone washed or not, I still wouldn't get on your boat and go farther from shore than I could swim, without a mechanical fastener made out of a flange and nut on the back, and sealed with a proper below the water line through hull adhesive sealant (5200 is used most commonly for this, and one of the few good uses for it) especially for a 3/4" hole in the hull. Epoxy is not flexible, all it would take is some rough waves to flex the hull and break the very weak bond between the epoxy and the stainless, and now that piece can potentially fall out leaving you a 3/4" hole in the hull.

using anything out of 304 is a big mistake in salt water. 316 is much more durable

:+1:
oops, I missed that the first time around

 

[CloudDiver]

For all the reasons listed above, plus I just don't think all the stainless is conductive enough, I think I will scrap this idea. Besides, mainsail hasn't even responded to the thread.

I will probably attach the Zincs to the keel the old fashioned way, but use a bronze through bolt and nuts rather than stainless. I can use a small counter-bore on each side and a small dab of 4200 to keep water out of the threads but maintain conductivity.