Prop Question

[Fishin Impossible]

Have a 225 Merc EFI on a 23' 1987 Osprey.Current prop is SS and has stamp that reads 17M? The rpm's only get to 4800-5000((40-43mph)) on a very calm day(w/o getting beat to death).
Don't have any experience with props and would like to know if the "pitch" needs to be Greater or Less than what it is?I'm assuming 17M means that it has a pitch of 17?The prop dia is about 13-14"guestimating..

Main problem being not enough power and develops a humming(whistleing)sound,leading me to believe it's the prop pitch...

Any help would be appreciated.
Steve

[JimCt]

If the motor's compression is good and plugs and all else is in order, less pitch will boost rpm.  Talk to your local Merc. tech or ask www.themarinedoctor.com for specific prop recommendations.

[Fishin Impossible]

Thanks for the info,will do....

[GoneFission]

Almost all Mercury propellers from 135HP to 300HP are ~14" diameter.  But there is almost no way yours is a 17" prop.  In order to do 43 MPH with a 17 on a Merc 225, you would need to turn over 6000 RPM.  I have a 22-2 CCP with a 200 Merc, and it does 40MPH wide open at 5500 RPM with a 19 pitch prop (also consuming 18 gal/hour at this speed!).  

My guess is that you may have a propeller in the 20-21 range, assuming your speed and RPM numbers are correct.  

A 17 or 19 pitch should be about right for your boat.  I would see if someone has another prop you could use/borrow/test to see what works for you.  

There is also a new composite propeller on the market called ProPulse that allows you to change pitch - and even replace a blade if you hit somthing - it's not quite as efficient as a good SS prop, but performs better than aluminum, and is not real expensive (under $200, with replacement blades around $20 each).  The ProPulse model that fits a 225 Merc has pitch adjustments from 15" to 21"
You can check it out at:
 http://www.propulse.se/

West Marine sells ProPulse (so do others, I am sure):
http://www.westmarine.com/webapp/wcs/st ... artial/0/0

Good luck!

[damnitbadger]

Have you tried Mercury Marines prop selector?
http://sites.mercurymarine.com/portal/p ... ema=PORTAL

[Ben87]

I can't really say what is what but as a comparison, my 87 222, when it had an 87 150 Merc would hit 5500 rpm and get 42-44 mph on the gps with a 15" X 17 pitch aluminum prop.  

The new 150 OptiMax I have, I put a 4-blade 15 X 16 pitch prop on and it will only get me 36-38 @ 5200 rpm, but at 4000 I get 30 mph and it gets out of the hole right quick and with less vibration overall from the motor.  I have not tried the 15 X 17 pitch prop I have since the boat was new but I suspect that that prop will get me back over 40mph if I put it back on.