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I just got back from the Bahamas, 180 mile run. When I put the boat on the lift I noticed the two collar style zincs recently put on in the yard had slipped. They traveled from approximately the middle of the shaft to up against the back of the strut.

I removed them today,

Any advice on installing two new ones so they don't slip again?

Steve-
Others here can advise you better but-
The shaft zincs I have used have a bronze BB set into each half. When I install the zincs I tighten them and then hit them on either side with a metal hammer. I think this sets the BB into the zinc and provides good conductivity. I then go back and tighten the allen head bolts again.
I am always surprised how a "tight" zinc sets and can be tightened some more after being set by the hammer.
Maybe you can install and use those zincs yet!
Best,
Stephan

Shaft Zinc:

Bronze BB:

Close-up of Bronze BB:

Stephen,
I just looked at them. They do have the BB in there, but it's flush now, already recessed. I can't read the size as the zinc has eroded some. Maybe they didn't put the right size on?

i used a dead blow hammer (lead hammer covered in heavy vinyl) that is the idea hit it on both sides and retighten a steel hammer like a ball pean would tend to bounce off. my humble opinion

Bob- good point about the hammer. Yes, a heavy one will do the trick. Rubber mallets need not apply.

Steve-
I previously purchased cheap zincs and had occasions when the allen head bolts broke or pulled the nut through the zinc. If you can't read the size might it be crappy casting or do you think they eroded quickly - like you have a stray current issue??
I also clean the part of the shaft the zinc is going on and give it a few passes with 400 grit sand paper.
I get my zincs at http://www.boatzincs.com/ and have had good luck.
Stephan

Steve

My money is on the fact that they were not tightened up enough. I have thrown them off towards the end of the season but in over 40 years never had them slip. I always hit them with a hammer to make sure they are on then tighten again.

If you have aluminum avoids use a deadblow hammer. Dam things are garbage. Dent easily and I find that the I can easily snap the bolts,

thanks guys! I'll purchase a new set and install them myself this time using your advice.

There's no worries about smacking the shaft out of alignment when hitting the zinc with the hammer?

Here's some choices on dead blow hammers at Harbour Freight. Size recommendations? https://www.harborfreight.com/catalogse ... low+hammer

I have a 1/2 dozen or so Cheap harbor freight Dead blows around here...they are cheap for a reason.

When I really need a Dead blow I grab a real tool like:

http://www.totalindustrialsupply.com/Pr ... lick=80157

They are hard rubber heads filled with shot. When you strike what you want to set, the face makes contact, rubber sticks holding head in place, a split second later the shot follows shocking with a good amount of force. Great for setting parts secure in vises.
The harbor freight hammers are plastic and load is somewhat off center on most...when you strike the plastic bounces and slides while shot tends to twist the head.
Better then a hard hammer, but I'd prefer a soft heavy brass or lead hammer over it.

I digress...2lb and give a couple good wraps on each side, go back and forth...just make sure your wrench is inserted all the way in head and your holding wrench or they go flying.
No, shaft will be fine your not going to apply that much force.

Usually I just tighten evenly then give a real good crank on one side, go to the other, crank and then back again...as it tights you'll get a ratchety pop pop pop as screw torques down.

One last question. Is there a recommended location for the shaft zinc? Center? Closer to strut? etc...

Keep several inches away from the strut to allow water to flow freely thru Cutless bearing.

Do not put to close to shaft log so water can move freely.

Aside from that, I have heard much reason to place here or there and not there or here...but never found any reason that made sense...so I go with anyplace your heart desires that is neither too close to strut or shaft log...and of course not too close to hull...I usually pick a spot that is easy to clean shaft and work....
Which brings me to clean the shaft to shiny for best anode contact.

I had them go the opposite direction and jam in the shaft log when I bumped the port engine in reverse 50 miles off the beach. We thought we dropped the gears and limped home on one engine. From that point on we always take a grinder to the flat surface of the seam on both halves. Not sure if that correct, but we seem to be able to get them a little tighter.

My $.02 on the subject of dead blow hammers from the perspective of tightening and loosening knock-off wheel hubs. Think of the dead blow hammer as the equivalent of an air bag in a supplemental restraint system. The bag's job is to spread the force of an impact from instantaneous to several milliseconds thereby lessening its impact on the alliding object (your face). A dead blow hammer does exactly the same thing as the air bag since the force of the impact is slowed by the hammer's padded surface and the increased time it takes for individual pieces of shot to reach their final destination as opposed to the solid mass of a cast steel or lead hammer striking a fixed surface. Think also of how the sharp rap of an impact socket can loosen a nut or bolt that resists all other effort. Dead blow hammers definitely have their place in certain processes, but if you want or need to exert maximum force there is no substitute for one hard object directly striking another.

No connection with this supplier, but quite popular in automotive circles: http://performanceunlimited.com/cobrava ... ammer.html

Because we hash things every way possible and it usually helps! Consider Godfrey zincs. They are great and have eliminated the slippage you talk about for me.

They are a tad more expensive but you only need one per shaft because they maintain contact with the shaft until they are gone so they last longer. I used to have to put two of the button style on to get me through a season, and that overall cost more and doubled my workload of zinc changing (not a big work load, lets be honest...).

Take a look and consider these.

http://www.godfreyboatzincs.com/

Dug

From the Godfrey site...

Godfrey offers the only corrosion collar with a unique brass core. This assures permanent electrical connection by holding the collar around the propeller shaft until all last traces

And it does work!!!!

Dug,
Thank you, I ordered a set.

My son looked at our old zincs and said, "Why wouldn't they make a shaft zinc with a core of no corrodable metal so it doesn't slip?".
I suppose they do!

In addition to hammering try a little blue colored Locktite on the threads.

These shafts spin fast, need to do it all. My first year the yard installed collars slipped. Now I apply a dab of locktite on the.shaft under the zinc, tighten, then tap tap tap, tighten again and repeat. Haven’t had another zinc slip in 20 years.