Prop shaft taper help!

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seafox67

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I'm changing a prop and measuring the taper for the very first time in my life!

The prop shaft looks like the original Volvo Penta supplied back in the late 80's.

I have measured it as a 25mm shaft with a 1:20 taper.

Now, the prop supplier has said that the taper is a bit unusual!

Can anyone remember back in the eighties if there was 1:20 taper used by Volvo?

Cheers
Paul
 
macd said:
An unusual taper, but not unknown. Have you perhaps calculated on radius rather than diameter?
Click to expand...

Definitely the diameter. I used one of those caliper things.

The big end of the shaft was 25mm (a 25mm prop shaft)
And the small end of the taper just before the the thread was 22mm.
The length of the taper part is 60mm
So, I'm thinking 60 / (25-22) = 20
 
seafox67 said:
Definitely the diameter. I used one of those caliper things.

The big end of the shaft was 25mm (a 25mm prop shaft)
And the small end of the taper just before the the thread was 22mm.
The length of the taper part is 60mm
So, I'm thinking 60 / (25-22) = 20
Click to expand...

Nothing seems wrong with your sums.

coaster63 said:
Hi just looked in this when i needed a prop ,
mine was boss length 57, front dia 25 aft dia 20 that = 10:1 tape
check out www.propellerpages.com/?c=tech_info&f=tapers
Click to expand...

That works out at 11.4:1, so take your pick :ambivalence:

On an old shaft, in particular, it's not always easy to see precisely where the taper begins and ends, which obviously skews the calculations. It's sometimes worth measuring the prop as well, if practicable.
 
coaster63 said:
Hi just looked in this when i needed a prop ,
mine was boss length 57, front dia 25 aft dia 20 that = 10:1 tape
check out www.propellerpages.com/?c=tech_info&f=tapers
Click to expand...

I originally tried to get the taper from measuring the prop itself but I'm convinced the previous owner has retro fitted the prop! The bore hangs over the thread and is a least 10mm past the taper at the other end.

I've gone by the measurements from the prop shaft (see photo) but with the prop supplier questioning the 1:20 taper has got me a bit worried!

I'm just wondering with the prop shaft dating back from the 80's this 25mm shaft with a 1:20 taper was standard back then with Volvo Penta?
PropShaft.jpg
 
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I bought a new prop from Norris's last year and ended up taking the old prop to them so they could check my measurements as they also queried it.

Mine was also a 20:1 taper from a 1980's Volvo powered yacht.
 
seafox67 said:
I originally tried to get the taper from measuring the prop itself but I'm convinced the previous owner has retro fitted the prop! The bore hangs over the thread and is a least 10mm past the taper at the other end.
Click to expand...

Paul: whatever the boss length, the old prop should still give you the taper ratio. (Assuming it wasn't an utter bodge, of course.)

You're fortunate in that the machining marks indicate the exact length of the taper. (Your 60mm line looks longer than that, but I presume just an artifact of your drawing?) Suggest you send the image to your prop supplier and ask for their comments.

P.S. Ardee's news, arriving whilst I was typing, is obviously good.
 
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Std tapers are 16:1 12:1 10:1.
It is not impossible that somebody desperately need a prop and one turned up that sort of "fitted" .
It is also possible that a 12:1 prop could be fitted to a 16.1 shaft and work for years without problems. !
It sounds like this may have happened from your description.
 
I am the last person in the world to query someone else's measurements, but subjectively (and measured with a bit of folded paper) that looks like more than a 3mm difference.
More like a quarter of the thick end, or 6mm.

But that could be perspective, parallax or a number of other things.

I recently went through the rather traumatic process of re-propping my 1988 Moody (Volvo engined) and everyone confirmed that metric = 1:10 and imperial = 1:12

But I see others have posted what is probably better info while I was typing that.

Yes. It's a slow day at work.
 
lampshuk said:
I am the last person in the world to query someone else's measurements, but subjectively (and measured with a bit of folded paper) that looks like more than a 3mm difference.
More like a quarter of the thick end, or 6mm.

But that could be perspective, parallax or a number of other things.

I recently went through the rather traumatic process of re-propping my 1988 Moody (Volvo engined) and everyone confirmed that metric = 1:10 and imperial = 1:12

But I see others have posted what is probably better info while I was typing that.

Yes. It's a slow day at work.
Click to expand...

My boat is a 1989 Westerly (Volvo engined). So I had been expecting something standard like 1:10 before I had took the measurements!
 
Yes, well, best of luck.
I took up the offer of professional help in fitting mine, but we still ended up b**gering the thread on the shaft, so I had to get the shaft re-tapped.
 
Aardee said:
I bought a new prop from Norris's last year and ended up taking the old prop to them so they could check my measurements as they also queried it.

Mine was also a 20:1 taper from a 1980's Volvo powered yacht.
Click to expand...

That's what I did too. It puts the responsibility for any error on them - the experts - rather than you, an amateur, which could be expensive.
 
Thanks for all your feedback and comments.

It's good to know that there are a few others with a 1:20 taper so I will put my trust in my measurements.... and hope for the best :)

Worse case... I will also be updating my prop shaft too ;)

I also got a response from Norris Marine (The prop supplier);
"Volvo tapers were mostly 1:20 but 10mm key was more common and the taper
length was usually a bit longer (70mm)."


Cheers and thanks
Paul
 
seafox67 said:
Thanks for all your feedback and comments.

It's good to know that there are a few others with a 1:20 taper so I will put my trust in my measurements.... and hope for the best :)

Worse case... I will also be updating my prop shaft too ;)

I also got a response from Norris Marine (The prop supplier);
"Volvo tapers were mostly 1:20 but 10mm key was more common and the taper
length was usually a bit longer (70mm)."


Cheers and thanks
Paul
Click to expand...

Glad you got there in the end. The 1:20 25mm Volvo shaft was indeed a standard fit in that period, although most Westerlys both before and after were 1" 1:12 made by a UK supplier. I believe the shafts came as a package when Westerly first started fitting Volvo 200X series rather than Bukh
 
If in any real doubt you can always get a simple female taper blank made up to the size you think it is and try it on the shaft. I did this to check if a shaft was 1:10 and not 1:12.

Yoda
 
Just a comment. Whoever turned that taper should be hung drawn and quartered for leaving a ridged finish like that. A smooth finish to the taper on both shaft and bore is needed to provide a good fit.
 
macd said:
Paul: whatever the boss length, the old prop should still give you the taper ratio. (Assuming it wasn't an utter bodge, of course.)
Click to expand...

And as the former owner of a bodged yacht I was pleased when Darglow, the vendor of Flexofold propellers, asked me to measure my shaft taper AND send them my original to the boat Jeanneau-fitted propeller.

The prop taper: 10:1. The Shaft taper: 12:1. Bodge city. Obviously someone had replaced the propshaft at some time using the most convenient (but wrong taper) 25mm shaft.

Result: Darglow re-tapered the boss of my shiny new Flexofold prop as part of the deal. An object of desire; it fitted perfectly and first time. Money well spent and faster under power and under sail too!
 
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