1 inch prop on 25mm prop shaft? - SailNet Community

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Old 11-27-2009
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1 inch prop on 25mm prop shaft?

Lost my prop last weekend. After hours of swimming in cold water, it looks like I'm going to have to buy a prop. Can I install a one inch bored prop on a 25mm shaft? Where do I find the right metric prop nut and anode for the old metric prop shaft on my 1972 Dufour Arpege. I'm in the Tampa Bay Area.

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Lawson Mitchell
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Old 11-27-2009
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It's not a good idea to put the wrong size prop on the shaft. The tolerances are close with a proper fit and you risk losing another prop if you try to fudge it. If you're buying new, any local propellor repair shop will be able to supply one with the proper bore.
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Old 11-28-2009
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Quote:
Originally Posted by lawsonmitchell View Post
Lost my prop last weekend. After hours of swimming in cold water, it looks like I'm going to have to buy a prop. Can I install a one inch bored prop on a 25mm shaft? Where do I find the right metric prop nut and anode for the old metric prop shaft on my 1972 Dufour Arpege. I'm in the Tampa Bay Area.

Thanks,
Lawson Mitchell

What is more important is the angle of the taper. Find out if the 1" prop has the same taper as you your shaft .

If it has the same taper then the only point to note is it might sit nearer the small end of the taper but there should be no problem.

the taper of some imperial props is 1 in 12 and the taper of some metric ones is 1 in 10 however if you have a 1 in 10 shaft and prop or a 1 in 12 shaft and prop then it should work for you. A good machine shop could alter the taper in the prop to fit.
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Old 07-10-2014
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Re: 1 inch prop on 25mm prop shaft?

I fitted a 1'' prop to 25mm shaft and dually lost it,though I did stop the motor twice running over heavy kelp at night coming into harbour, I was lucky in that because I hadn't put her into reverse to clear the kelp I managed to motor into the marina and lost her when I put her into reverse or neutral inside the marina, no damage, dived for hours-never found it.on the good side I replaced with a kiwi prop,briliant.
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Old 07-10-2014
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Re: 1 inch prop on 25mm prop shaft?

Can a prop bored for a 1" or 25.4 mm shaft ay 12/1 taper be machined to fit a 25mm shaft at 10/1 taper.

Nope don't think so.

Pony up for a new one and be thankful it was not a Max Prop you lost.
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Old 07-10-2014
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Re: 1 inch prop on 25mm prop shaft?

The difference is .4mm. Not too much of a difference. The taper has a greater significance, but the keyway takes a lot of the force. The nut should be metric though. I would use a readily available cheap 1'' prop until I could find a better overall prop, during haul out.
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Old 07-11-2014
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Re: 1 inch prop on 25mm prop shaft?

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Originally Posted by sony2000 View Post
The difference is .4mm. Not too much of a difference. The taper has a greater significance, but the keyway takes a lot of the force. The nut should be metric though. I would use a readily available cheap 1'' prop until I could find a better overall prop, during haul out.
The taper is the problem, you will not get the prop to seat.

Running with a loose and or out of balance prop will cause damage, possibly very considerable damage to the shaft, the cutlass bearing, shaft seal, maybe the P bracket and maybe even the gearbox. Please don't do it.

Especially as the price for a new prop WILL BE THE SAME regardless of the shaft size and taper.
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Last edited by TQA; 07-11-2014 at 11:13 AM.
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Re: 1 inch prop on 25mm prop shaft?

Yes anyone running a loose prop would be out of their mind.
Buy a used one. You could be 11X7 RH X 25mm.
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Re: 1 inch prop on 25mm prop shaft?

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Originally Posted by sailorbill1 View Post
I fitted a 1'' prop to 25mm shaft and dually lost it,though I did stop the motor twice running over heavy kelp at night coming into harbour, I was lucky in that because I hadn't put her into reverse to clear the kelp I managed to motor into the marina and lost her when I put her into reverse or neutral inside the marina, no damage, dived for hours-never found it.on the good side I replaced with a kiwi prop,briliant.
You shouldn't be able to lose the prop if its installed correctly with the castle nut and cotterpin.
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Old 07-12-2014
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Re: 1 inch prop on 25mm prop shaft?

Mixing SAE & Metric is a mugs game. It's bad enough when you have both types on the same boat or car but to mix them on the same piece is asking for it - they are NOT the same, even though they get close some times.
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