Maxprop pitch?

[rvink]

Recently a 17" Maxprop was fitted under my SO 34.2 Athena.
Since then I hear a lot of noise in the cockpit which I think is cavitation.
At full throttle the engine revs only 2900 rpm instead of 3600.
Could this noise be fixed by adjusting the prop to a lower pitch?
Before the Maxprop she had a 16" fixed prop (standard).

Thanks in advance,
Rob Vink
SO 34.2

[gene]

You are over propped. Reduce pitch by 200rpm/in if I remember correctly. Or about 4". Hard to say if it will eliminate noise but your engine will last longer.

Gene

[rvink]

Thanks Gene!
The 200 rpm/inch (on the prop shaft) seems to be a good standard I found out. Will change it as soon as there's an opportunity.
Regards,
Rob

[gene]

Ah yes, shaft RPM. Note that if you kept the pitch the same when you went from 16" to 17" you would have dropped the shaft RPM by 200 also (200 RPM per inch pitch or dia). So if you have a 2/1 ratio that would explain the drop in engine RPM.

Gene

[MartyB]

"IF" you can find a good diver, the pitch can be changed in the water in about an hour or less IIRC.

If you know the motor, rpms etc, along with the disp of your boat, let me know, I can call PYI, the US distributor and get the pitch etc for your boat, they are all of maybe 5-10 min driving, and a local call.

Marty

[rvink]

Hi Marty,

I was away for a while so sorry for my late response.

The displacement of our SO34.2 is 4650 kg or 10252 pounds. She has a 27 HP Yanmar 3gm30f. The waterline length is 30 ft. The prop is 17".

Hauling out cost me at the club around 50$ so a diver won't be necessary!

Thanks in advance, Rob

[MartyB]

Rob,

I'll give them a try tomorrow. it is about 8 pm as I type this on the west coast of the US, not sure where you are, other than you were writing at 130AM my time...... Europe?

Marty

[rvink]

Hi Marty,
thanks!
I'm living in the Netherlands. Regards, Rob

[MartyB]

Rob,

Can I assume a 3 blade? as I was sitting down to call this morning, I went, 2 or 3 blade?!?!?!?!?

Marty

[MartyB]

Rob,

Here is what I found out. If you take your current pitch setting, say it is 24 degree. lower it to 22 degrees, and you will up rpms to 3250, lower to 20* and you will have 3700 rpm to work with.

This is assuming you have as they said, a clean bottom, smooth seas etc, and the pitch of the prop is what's keeping the motor from reving up all the way. This did not matter if your prop was a 2 or 3 blade.

Hope this helps.

marty

[rvink]

Marty,

thanks for your help! I will plan a haul out and have the pitch lowered probably to 18 degrees (it's now 22).
It's a two blade maxprop.

Regards,
Rob