SO 35 propeller size and vibration problems.

[Willie D.]

Hi.

I have a 2005 Sun Odyssey 35 with a Yanmar 3YM30 engine married to a Kanzaki KM2P shaft drive gearbox with a large two blade fixed prop.
Can anyone tell me the correct size of prop for this boat ?(as the boat is in the water I can't obtain the measurements). 

Also, I have replaced the two rear engine mounts with a different make to those on the front although both types are the correct rating for the engine. Should I have replaced all four using the same make?  The rear mounts were scrap but the front two look perfectly good and the metal to rubber bonding is in good condition. I don't know how old they are?  

Any advice would be welcome.

Regards.

Mynabird.

[Don Reaves]

I'm pretty sure that the original 2-bladed prop on my 2004 SO 35 is 16 inch diameter, 12 inch pitch. I replaced it with a 3-blade 16.5 inch diameter KiwiProp. Since the pitch is adjustable, I couldn't tell you exactly what it is set for. Having a propeller with too large a diameter can certainly cause vibrations, but neither of my props caused a problem.

As for the engine mounts, I'm no expert, but it seems like having four good mounts should be adequate, even if they're made by different manufacturers. Perhaps someone on the forum has more information on the subject.

Don

[Charlie-Bravo]

From memory mine is a 16x12 two blade fixed prop ( not close to my recorded notes at the moment) and not sure that is or was Jeanneau's original.

Two blade fixed props are prone to a bit of vibe mostly due to the disturbance of the water flow behind the P bracket, and perhaps minor balance issues, mine is silky smooth up to 2000 rpm a bit of vibration from 2100 - 2600 then smooth with increased revs through the 3000's where the noise of a thrashing engine becomes more noticeable than the vibes, the fuel consumption goes up and it becomes a little wearing.

Having mentioned your new engine mounts .... did you replace the cutlass bearing at the same time?

what actions/ tests did you do to ensure good shaft alignment?

What revs are you finding bad vibrations at?

and is this a new phenomenon?

I would have replaced all the mounts, having blocked up the engine,  it's not just the vulcanised joint of metal to the rubbery bit that sufferers, the rubbery bit gets a bit squishy with age, so you might have squishy old ones at the front allowing more misalignment under load than with a full new set,  provoking a few vibrations.
The mechanics of it all is a bit crude, slight misalignment will occur whilst accelerating, the engine rotating on its mounts not around the shaft centre,  and rotating things vibrate worse at certain revs it's just the way of it, harmonics / balance etc, new mounts sag with time so re align the shaft toward the end of their first season, after which it will probably have settled in. and on the whole not too much of a maintenance issue, you will only replace them once every 6-10 years, first signs being drippy dripless shaft seals and cutless bearings not lasting for too long.

I would like a folding / feathering 3 blade, a real upgrade for smoothness and perhaps better protection from lobster pot lines along with another half knot or more sailing speed , the only benefit of a fixed two blade is the lack of moving parts below the waterline , less to go wrong ( plus price I suppose ), I used to suffer ' Brunton anxiety' (a well documented ailment) with my last articulated prop, a noisy clunk when engaging drive known as 'Brunton clonk', followed by much wondering if all the blades were still there ! a great prop ... but too expensive for me this year and probably next year,  any forum member with a suitable prop ... going for a song, just let me know and I'll start singing!

CB

[bereboot]

I have a 3 blade lefthanded flexofold from my so39i for sale. Propshaft diameter 30mm.if interesse you can contact me  [e-mail] 

[zaphod]

Jul 20, 2021 14:18:37 GMT bereboot said:

I have a 3 blade lefthanded flexofold from my so39i for sale. Propshaft diameter 30mm.if interesse you can contact me  [e-mail] 

I doubt very much a 39i prop would be suitable for a SO35. The 39i has a much more powerful engine and a different transmission. My 39i came with a 17" 3 blade fixed prop.

Why are you selling your Flexofold? I put one on my 39i and I love it!

[Don Reaves]

If nothing else, the shaft diameter is too big for the SO 35.

[Charlie-Bravo]

Thanks for the offer Bereboot, but as said above , will not fit the boat, no doubt you will find a new owner for it, they have a good reputation.
CB

[gre2]

We have a SO 37 and with a two blade prop there was a lot of cavitation. Switched to a 3 blade Kiwi prop and there is no cavitation and also no prop walk to port. Win Win.

[panoramix]

I have an 2003 SO37 with the Radice 16 x 11.50 RH prop from the factory. This prop is ideal for motorsailing.
For motoring only it is a bit oversized and has a lot of cavitation. Which in turn produces the vibes.

As for the engine mounts. I replaced mine last year and noticed that the old ones had sagged 3 mm down.
With the new mounts the engine/propshaft alligns much better!

[vasko]

proper size is 16x12 - but I'm with 17x13 and very happy with it

[Willie D.]

Hi.

Thank you for all the advice.  I now have a lot of valuable information to work on.  I had not thought of cavitation so perhaps a new three bladed folding prop would solve the problem along with new front mountings and proper alignment.

Thanks again.

MB.

[NZL50505]

I’ve always found feathering better than folding. Notably performance in reverse.

For any given rating the Maxprop seems to have a smaller diameter than average which is offset by ‘fatter’ (less elongated) blades which give more surface area per blade. Result is more hull clearance (and potentially less interference / vibration) but same thrust.