prop attachment on A25

[kerrye]

Question about prop attachment. I think my boat has the original prop shaft because it has the original grease filled stuffing box. The prop is trapped between two nuts one in front of the taper and one in back of the prop. I believe the installation procedure is to slide the prop onto the taper tighten the Stern nut and then tighten the front nut down on the front of the prop. Is this the original method for holding The prop on the shaft? There's not much room for a zinc on the prop shaft with the nut in front of the prop

It also has a stepped key with the slot in the shaft wider than the slot in the prop. I assume this means my prop isn't original?

[hetek]

That's odd. I don't recall ever seeing a nut on the front side of a prop. Then again, I haven't seen everything.

My A25 has what I would call a more traditional setup. I have the 30 mm original size shaft (though might not be original to the boat), also with the grease type stuffing box. It has the prop seated on the taper and a castle nut with cotter pin on the back. Done.

My other inboard boats had the two nuts on the back of the prop. The second nut was a jamb nut.

Again, might not be original. I know the 50 hp Westerbeke that was on the other end surely was not.

Just wondering... If the nut on the front was ever tightened, wouldn't it in effect try to push the prop off the taper?

[Beta Don]

That's odd. I don't recall ever seeing a nut on the front side of a prop. Then again, I haven't seen everything.

Just wondering... If the nut on the front was ever tightened, wouldn't it in effect try to push the prop off the taper?

I agree - Very unusual

I've never seen a factory A25 out of the water, but I've also never seen a nut in front of a prop on ANY boat and I don't have a clue what it's purpose would be. The reason they use a tapered shaft is to apply tremendous pressure when forcing the props taper against the shafts taper - Tightening a nut in front of the prop would only lessen that

If the keyway on the shaft doesn't match the keyway on the prop, I would guess that the forward nut was some previous owners idea of a 'band-aid fix' to a bigger problem. IMO, time for a new prop, a new shaft or both. The key and both keyways need to match up correctly

Don

[kerrye]

I agree that it seems odd and I don't understand the purpose, especially since it pushes against the taper. Someone had to thread that shaft so it doesn't seem it could be just an accident. From what I've been told, stepped keys are not unusual and are commercially available. I don't think the step causes any problems as both sizes fit snugly in their slots.
The stern most nut is a castle nut and should have had a cotter pin. When I got the boat it didn't and it was obvious none had been there for years since the hole in the shaft was filled with bottom paint.
I don't see any reason to replace the existing system since it seems to function fine. It's just very odd.

[dkirsop]

The nut in the front is to remove the prop. A very handy feature. The key ways for the prop and shaft should be an exact match, a sloppy fit is bad news which can eventually result in shearing of the key. A prop nut with cotter pin and anode is standard for corrosion protection.

[kerrye]

Aaaaah. That makes sense now. There isn't any sloppiness to the key, just two different widths. Anyone have a link to the right kind of nut/anode combination? A quick search didn't reveal a nut with a cotter pin and an anode together.

[hetek]

Thanks dkirsop! Makes perfect sense now. A "built in" prop puller, or pusher as the case may be. I like it.

[dkirsop]

My boat has a 25mm shaft and uses a Type B anode nut.

[WillieC]

Yup, built in prop puller. A critical measurement I made sure not to lose when I had to shorten my shaft for the longer transmission. Anode in front of that with about 3/8" clearance behind the cutlass. The new, composite cutlass has 4 holes in the side though.