Prop shaft end zinc coming off

[Celestialsailor]

In April, I did a haul out,which among other things, gave me the chance to change the prop shaft zinc. On the old system, the shaft came out of the cutlass bearing a 3/4" then tapered for the prop. So a collar zinc ever only had half a clamps worth. The other end of the shaft that born the shaft nut was too close to the keel hung rudder to accommodate a shaft end zinc. Solution?...shorten the shaft an inch, tap the end of the shaft 5/16"-18 and use a shaft end zinc (pictures attached). I thought I had tightened it sufficiently. Mid August, I had the bottom cleaned and zincs inspected. I was informed my end zinc was gone, machine screw and all. There is only 3/4" behind that zinc to the rudder. You would think if it came loose, you would feel it hitting the rudder as to put it on, the rudder has to be turned off to the side to install it.
I'm on my way south now and in Santa Cruz visiting some friends. I had a diver a few boats down install one of my spares. I put Red Locktite on the machine screw. The diver placed it on, hammered it home (not too hard I hope) and used my extra long Allen wench and he said he really heaved down on it.
My question is....has anyone else lost these zincs?

[White island]

I have the same problem. I would not want to mention that a jack leg mechanic named TJ, located near Aqua marina, in lake Pickwick, made my new shaft. and did not leave space for a zink. so I have been planning on using one like you did. I will be sure to tighten it well when I do. I hope it stays on. PS steer clear of the aforesaid jack leg. he charges double the quote and does half the job.

[Celestialsailor]

Good thing you don't want to mention TJ located near Aqua marina, in lake Pickwick.

[zeehag]

i use a colllar on my propshaft.

i have heard of many of these end caps having problems. folks modify them differently.


i hope it stays...... bring spares when you sail---hard to find zincs here.

[Celestialsailor]

Thanx Zee...I was considering a through side hole and a 1/4-20 nut and bolt. I have also see on the inside of a boat, a copper wiper that touches the shaft while turning on an arm, connected to a plate zinc outside the boat via a wire. maybe someone can turn me on to a distributor for this.

[twinboat]

I found the one on the left can't fall off, unless you lose the nut.

[twinboat]

campcompany.com/replacement-anode

[Capt Phil]

If you re-tapped the shaft to accept the SS screw, which way did you tap it? Should be tapped counter to you prop turn direction otherwise it will spin itself off in short order. same with putting threads on the shaft. Phil

[hellosailor]

Red Loctite? Is that supposed to not fail totally when applied underwater? Set screws can also be staked, that might hold better.

[bobconnie]

Props were kept on for a long time before Loctite was ever available!! Get em TIGHT and stake em!! as Hellosailor said!! The only prop Ive ever had come loose, was after it had 100 ft of crab line wraped around it !!!

[Celestialsailor]

Originally Posted by Capt Phil

If you re-tapped the shaft to accept the SS screw, which way did you tap it? Should be tapped counter to you prop turn direction otherwise it will spin itself off in short order. same with putting threads on the shaft. Phil

The inertia of a 5/16 machine screw at the rpm of the shaft would be ounces of force, so I doubt that would have a bearing on it. They are probably torqued to around 25 ft./pounds.

[Celestialsailor]

I had a diver in Santa Cruz, Ca. put another end zinc on. This time the diver tapped it on with a hammer to ensure a firm fit, then I used a little red loctite on the threads. I have no idea if loctite cures underwater but it can't hurt. I'm in San Diego now and it's still with me.
I noticed that the general design of the zinc has a tapered area where the nut fits into it. This is called "draft" in the mold making industry. It facilitates the unit being released from the mold easier. However, it inhibits the bronze nut from seating properly, I think. I would have to cut one lengthwise in half to see if this is the case.