Electrolysis Protection?

[Mark Johnson]

Most stern tubes these days are fiberglass. I'm surprised that yours is SS.

The thin sleeve around the cutlass bearing will be fine. I have never heard of one corroding out before it wore out...

A Bronze stuffing box nut assy. can be inspected from the inside by loostening it, and pulling it back. If the interrior of the bronze part is not decidedly "pink" under the surface scuzz, it is either not corroding, or it is minimal.

I put a shaft brush on the shaft's "interrior end", so I could bond it to the bronze strut with an interrior wire. This way the zinc at the prop end protects the prop & strut. This would apply to other bonded metal within about 8' as well. (IF they are electrically connected).

SS is not all the same! In our case, the "Aquamet 22" SS shaft has been blemish free for its 15 years in the water. Not a single pit or spec of rust, (even inside the stern tube). Only our bronze parts are vulnerable.

Each boat is unique. The electrolosis protection system that works on one boat, will not necessarily work on another sistership. I started out with seperate zincs on my lightning protection ground plate, and later removed it, as it was unnecessary and the exess "juice" attracted barnicles. I also started out with zincs on my polished, underwater, SS gudgeon & Pintles. I later roughed the hardware up, applied an etch/primer kit, and now bottom paint them. Both of these systems are fine with no zincs, they are not bonded, and my only shaft zinc protects the bronze prop, strut, and SS shaft.

IMO... A good starting point would be for you to protect only the shaft & prop with a single shaft zinc near the prop. Then over time, inspect the stern tube & stuffing box gland interrior, to see if it needs additional protection. You don't want to "over zinc", as this opens a can of worms too.

Mark

[redhead78]

Ok, I have a center cockpit, what I am calling the shaft tube or log starts at the at the engine side of the engine compartment,the stuffing box is attached here. The shaft tube goes under the cockpit and at the very rear where it comes out is what I call the stern tube that holds the cutlass brg.The inside of one of the stern tube bolts had a small ground strap attached I did not know about, and when I was finally done turning the bolts and pulled them out it became twined around the bolt. I am planning on a zinc doughnut. What I was asking is at the stuff box end I can attach a wire, but where do I terminate it, or do I not need it with the zinc on the shaft? Red

[redhead78]

Nick here are a couple of pics. See where the shaft comes out without the stern tube, on the bottom bolt was a wire. When I reinstalled the stern tube, my buddy was inside the boat , the 42" tube was out and he had a 3/8" drive ratchet, with a 4' extension, blind it took us about 40 minutes each, just to get the nuts and washers started. I put heavy grease in the 12MM socket to try to hold the nut and lock washer, while I carefully turned a screwdriver from the outside.

[Mark Johnson]

If I read this correctly... there is a bonding strap inside the stern tube??? that electrically connects the outer "cutlass bearing housing" to the inner "stuffing box hardware"?

If this is the case, you can use a bare engine bolt, or better yet a "shaft brush", and run a wire from it to the stuffing box using a hose clamp. Now the shaft, prop, and both end fittings... (Cutlass housing & stuffing box), are electrically connected. This will make it where the prop's shaft zinc will protect everything, except perhaps the inside stuffing box hardware. It will get the least protection because of the poor water flow in the stern tube, but this the best you can do. You can't get a zinc IN the stern tube, and one inside the boat, even if connected to the stuffing box, will not help unless it is under sea water. YIKES!

Hope this helps... M.

[redhead78]

Thanx Mark, one more thing, how bout a new bronze tri flange thru hull fitting I installed. they make a zinc for it.???

[fstbttms]

Originally Posted by redhead78

how bout a new bronze tri flange thru hull fitting I installed. they make a zinc for it.???

Provide a pic or manufacturer and part number please.

[redhead78]

Its a groco bronze tri flange adapter base for a thru hull 3/4", # gro-Ibvf750. Red

[fstbttms]

Originally Posted by redhead78

Its a groco bronze tri flange adapter base for a thru hull 3/4", # gro-Ibvf750. Red

No zinc made for a part like that.

[Mark Johnson]

Originally Posted by redhead78

Thanx Mark, one more thing, how bout a new bronze tri flange thru hull fitting I installed. they make a zinc for it.???

I'm not sure if this is what you mean, but if it's the interrior half of a bronze through hull, and has a mushroom head half on the exterrior, that threads into it, AND if it is within about 6' of that shaft zinc, then you can attach a bonding wire from the interrior base to the shaft brush. Then... both ends of the sterntube's fittings, the shaft, prop, AND this new through hull, are electrically connected. Only this being "electrically connected, in close proximity, in seawater", makes it where one shaft zinc will protect them all.

As I said earlier, sometimes "nothing to protect them" works best. This is more VooDoo than science. The science is very cut & dried, but since alloys vary so much, and it is more the interaction of the underwater metals than anything else, sometimes it just doesn't work like we expect it too.

You could leave it unprotected for the first year, then on the next haulout scrape off the scale. If it is Brassey colored, it is fine. If it is pink, the zinc is leaving the alloy and it needs protection.

Trial & hopefully not too much error...

Mark

BTW I ALWAYS use Marelon plastic through hulls, seacocks, & raw water strainers to avoid these issues.