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Old 02-03-2021, 21:30   #1
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Probably a simple question - is the shaft size inside the boat same as outside?

2005 Beneteau with Yanmar 2GM20F and Kanzaki KM2P transmission, trying to find out the size of the shaft so I can shop for a folding prop. Dealer is unable to help because their system has been down for 2 weeks now.

It should be either 25mm (more likely) or 1" (less likely) from what

So the question is - the shaft coming out from the transmission and going through the seal is probably not the same size as the shaft outside, right? I would imagine that they can, but don't have to be the same.

So is my only option to actually measure the actual shaft where the prop is installed?
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Old 02-03-2021, 21:56   #2
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

I have never heard of a prop shaft that changed diameters from one end to the other. I am reasonably sure that it will be the same throughout its length.

Now, do you know what taper it has? These do vary from one shaft to another, and must be accurately matched to the prop.

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Old 02-03-2021, 22:30   #3
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

Jims right, the prop has to match the shaft taper and key way exactly. The easiest way is to take the shaft to the prop supplier and let them get it right. I tried to do it your way but the prop guy wasn't interested unless I brought the shaft in.
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Old 03-03-2021, 00:48   #4
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

Might be easier to take the prop off and take it into the prop dealer, you're going to have to take it off anyway. Take the nut as well.
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Old 03-03-2021, 01:43   #5
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

FWIW, I have just swapped my fixed prop with a feathering Autoprop. I have a Beneteau Oceanis 31, 3YM20 engine, KM2P-1 transmission — mine was a 25mm ISO tapered shaft.
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Old 03-03-2021, 06:30   #6
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

A new shaft, same diameter with correct taper is not too expensive if it comes to that. Just one option.
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Old 03-03-2021, 06:35   #7
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

Quote:
Originally Posted by RaymondR View Post
Might be easier to take the prop off and take it into the prop dealer, you're going to have to take it off anyway. Take the nut as well.
Indeed.
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Old 03-03-2021, 11:06   #8
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

You would also want to lap fit the new prop to the shaft.
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Old 03-03-2021, 11:31   #9
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

George,

OK, my boat model is different (Jeanneau 43ds) but most definitely the shaft is the same all the way from the attachment to the gearbox to the prop. Mine is a diameter of 1 3/8" (35mm). I thought i might have trouble with dimensions & taper but got my feathering prop (a "Featherstream" 3 blade) from Darglow Engineering, UK who sent it to me in Italy, expertly packed. They already knew exactly what the standard Jeanneau taper was and had already supplied a number of 43ds owners with feathering/folding props.

If you want to see what your options are i suggest you read the Yachting Monthly review March 2015. I have tried to attach it to this message but it tells me "invalid File" even though it is WORD). I had a Maxprop on my previous boat and chose the Featherstream since it has almost identical performance characteristics to the Maxprop and was about 25-30% cheaper. While i went direct to Darglow who actually make the Featherstream there is a prop distributor with whom i see Malcolm negotiated a discount. Best of luck.
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Old 03-03-2021, 11:59   #10
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

When I bought my Flex-o-Fold two blade prop, the Flex-o-Fold salesman at the boat show just asked me what engine and transmission I had and the diameter of the shaft (7/8"). When I got the new prop, it fit the shaft taper perfectly, but the blades were a bit too long and would hit my rudder's skeg.

They swapped the original blades for shorter ones and all was hunky-dunky.

I find the service of Flex-o-Fold to be excellent.

I did have to buy their prop puller and that was really worth while.

The Flex-o-Fold also reduced the prop walk when in reverse.
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Old 03-03-2021, 12:13   #11
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

Quote:
Originally Posted by George DuBose View Post
When I bought my Flex-o-Fold two blade prop, the Flex-o-Fold salesman at the boat show just asked me what engine and transmission I had and the diameter of the shaft (7/8"). When I got the new prop, it fit the shaft taper perfectly, but the blades were a bit too long and would hit my rudder's skeg.

They swapped the original blades for shorter ones and all was hunky-dunky.

I find the service of Flex-o-Fold to be excellent.

I did have to buy their prop puller and that was really worth while.

The Flex-o-Fold also reduced the prop walk when in reverse.
Just added a Flex o Fold to my Pearson and had the same experience. CS was great. Tapers are almost always to SAE or Metric standards. Have yet to find a prop that isn't. Flex o Fold sent mine with the standard US taper and it fit perfectly.

And same thing, almost zero prop walk. Actually miss it at times as I used the prop walk (left hand prop) when docking starboard side to to bring the stern alongside the pier.

Also great power in reverse, more than my three blade fixed prop and extremely smooth. Love it all around.
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Old 03-03-2021, 12:42   #12
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

Hi all, CaptVR here;
Shaft and prop shops change props every day without pulling shafts and taking them to a shop. Could you imagine pulling a 2-3-4 inch shaft, 10-15 foot long. You would have a $1000 bill to change a prop if you needed to pull a shaft on a fifty foot boat to check taper. Many sailboats, have to have rudders pulled of to pull out the shaft's. These scenero's would all require a boat hauling to change a prop. No, not done.
You need a cheap HF digital caliper. Measure either the prop or the shaft. Measure the diameter of the large end where the taper starts, this will be the shaft diameter, now measure the shoulder on the small end where the nut tightens, it is easy to measure this diameter with the nut on against the shoulder. Put flat side of caliper jaws against the nut. That's the minor diameter, now measure the straight line length between the major and minor diameter. This is the only measurement the shop will need to check or machine the new prop to. And no, lapping a new prop to a shaft is not normally required.
A one inch shaft will be close to a 2degree taper, but like I mentioned, virtually all tappers are the same per shaft diameter. Shops have sets of tapper reamers to fine tune tapers in props jf required. I've changed and machined props and shafts in my shop for close to 55 years.
When installing a new prop, or a new shaft and you want to verify fit. A little Prussion Blue in a dab of grease mixed together, put a thin film on the shaft, slide the prop on, bump it forward lightly and pull prop back off. If there are any irregularities, they will show up with the Blueing. You should have a nice even coloring down the whole taper.
Hope I helped a little, and for $15 bucks, a pair of Calipers comes in real handy on a boat.
Take care all, happy sailing with pleasant winds.
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Old 03-03-2021, 16:06   #13
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

Thanks for the feedback everyone.

I have a caliper and plan on measuring the shaft coming out of the transmission. I was hoping to get a diver to swap the prop when the time comes as I would really like to have it on before my next haul out.

I'm currently looking at Flexofold 2 blade (lowest cost over fixed prop) or maybe Kiwi prop, because 3 blade is smoother, self pitching, and relatively inexpensive.
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Old 03-03-2021, 16:53   #14
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

Be aware a diver will not be able to confirm the taper will exact. See posts #2 & 3 above.

The correct way to fit a new prop to an existing shaft (or vice versa) is to lap the prop / shaft taper. This can't be done until the prop is offered up to the shaft. There should be greater 90% contact with 100% contact being preferred.

I do not know of any way this can be done by a diver in the water.

However some divers (and some owners) either don't know or don't care about doing the job properly. A poor initial fit can cause a prop to loosen with use and ultimately fall off.

You can do the lapping yourself if on the hard - it isn't difficult, might take 30 or so minutes if you aren't familiar with the process.

Of course, you can pull the shaft and have it done by the prop supplier but that is much more work and dollars.

Or you can take a gamble and not worry about doing it right
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Old 04-03-2021, 09:40   #15
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Re: Probably a simple question - is the shaft size inside the boat same as outside?

On a boat this size it is most highly probable that it is the same piece you are looking at. On larger vessels it might change due to there being an intermediate shaft which is often made of a less expensive but more corrosive material that is better able to withstand the forces upon it.
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