Propeller zinc??

[tribologist]

My propeller shaft does not have a zinc anode. Boatzincs sells one for 3/4-UNC thread that looks like it can work. Do people use them? I don’t see them at Defender etc.

Ulf

[hetek]

I'm using a "limited clearance" 30mm zinc collar on my shaft, although my shaft was just built to my spec's so yours might be different.

I got mine from boatzincs.com.

[WillieC]

Are you talking about a bullet style zinc aft of the propeller? Since there is no room on most of these A25s for a bullet zinc, many of us use collar type in front of the prop. That real estate is tight as well depending on whether or not you have the handy-dandy built in prop removal nut threaded onto the shaft in front of the prop.

I have heard that the bullet style, if you can get it to fit, is preferable. Maybe for more hydrodynamic water flow and better rotational balance. Once my donut zinc starts eroding, I am sure it contributes to the racket under way. And its square edge profile surely knocks a knot or two out of my top speed. (Some get the sleeker bulbous style to fit ahead of the prop.) Another consideration is leaving enough of a gap at the cutla(e)ss bearing for water flow. And my transmission (mated to the original MD3B VP engine) pulled the shaft forward and aft about a quarter inch between forward and reverse.

You are doing an amazing job there. You will know this boat. Our PO kept his boat in a marina and hired divers for zinc replacement and who knows what else. When we got it home and put it on our newly built trailer, I discovered that they used a not quite fitting SAE zinc on the 30mm shaft. Minimal contact at the interface, now growing crud inside there. How much did that fine piece of "maintenance" cost him? How confidence inspiring is that in hiring the simplest of projects out?

Keep going, and thanks for keeping us posted.

[kerrye]

I have no zinc on mine either and I'm curious as to whether you can get one on the prop nut.

[tribologist]

Thanks! The only thing i hire someone for is wheel alignment... might not do that again either, one of my buddies race cars and he just bought a setup... I went and measured after i read the post and i would have a 10 mil clearance... i might buy one and look if it can be modified. A bronze barstock piece is looking more and more attractive.... would not be hard to make a nut that i can clamp an acorn zinc over. Once the prop is on I doubt it take much to hold it. (Im more concerned of how to pull them off.)

Ulf

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[RobS]

Since you like to tinker (should be a requirement for all boat owners) you might consider a shaft wiper tied to a transom zinc.

[Dieselram94]

This is interesting, I was reading the other day snout corrosion in stern tubes, should a zinc be not only on the prop, but also somehow attached to the stern tube? Maybe at the cutless somehow?

[tribologist]

Got the spinner zinc on there. Its on the tight side so it will meet my friend lathy lathe face and get a 1/4” trimmed off. The innards comes with a brass washer that can be trimmed down considerably and the zinc can be cut back to. The part i like is that the prop nut now has a nice positive lock with a castellated nut and the reduction in drag that will easily give me 1-2 knot on the top speed.

Ulf

[kerrye]

I assume you didn't have to pull the rudder to install that? What are the exact dimensions of that zinc. I'd like to install one on my boat to get that same 1-2knt increase.

[WillieC]

I can get a 1-2kt speed differential, either direction, by picking what conditions I go out in without touching the zinc.
That install looks very nice, and I think it is better than the collar type I am using, but I don't have enough room between end of shaft and leading edge of rudder. Soon as DA coughs up for new shaft, I can fix all that.

[tribologist]

It was easy to install. Just turned the rudder. I will measure it before hacking into it with the lathe. The Boatzincs webpage has the dimensions listed but i will check them.

I was thinking on the shaft issue last night. It should be possible to flip the shaft over and cut a taper and thread on the old motor end and make an adapter for the taper to fit the coupling. Kind of like my mom used to flip the shirt collars when they got worn in the neck...

Ulf

[WillieC]

Hmmm...a taper, with or without an adapter for mismatched tapers, works on the prop end because of the nut, at least to my way of ciphering. How would that work on the engine end? Short of welding it back up and re-turning it, which plan would be much easier at the cutlass location.

There is a guy with the killer beard back east who runs a machine shop and posts a bunch of videos of this sort of repair. Looks easy peasy from my recliner. I especially like his vids of casting babbit bearings, something my dad, The Ancient Machinist, spoke fondly of. Long ago, with my first wife, we visited the old homestead back in Pa. Cousins and other shirttail relatives still work(ed) in the foundry in New Wilmington (maybe Ellwood City, I forget) where they made crankshafts for serious engines, like you guys have in the 28s, the Old School Way. Need a conrod journal? No problem, just heat that section of the fifty foot crank to about a jillion degrees C or F, don't matter, and yank it out with dese here pincers on dat dere forklift. Careful, don't burn yourself. Not quite? Back in the oven. Then after a few hundred years when it cools down, it gets machined to actually look like a crankshaft. Amazing.

So, yes. You prolly can flip it around. Don't burn yourself.

[tribologist]

Making a new taper on a 1” shaft is easy. Its only 2-3/4 long so with some care it can be done with the compound slide. My compound has 3-1/2 travel. I was thinking of making a sleeve that has a matching taper on the ID, cut it for the key and put a custom key in. Either hold it with the original nut or make a smaller nut. The other option is to make a new flange with a tapered bore. Bring it if you are visiting your family in Pa and we can give it a try or have DA bring it whe he is coming to fix his trailer.


Ulf