4 blade prop- 18' OR - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  4 blade prop- 18' OR

search | FAQ | profile | register | author help

Author Topic:   4 blade prop- 18' OR

acseatsri posted 09-05-2001 09:49 PM ET (US)
I'm trying to decide on a pitch for my Outrage. Currently running a 3-blade 14 1/2 x 19 pitch, WOT about 5100 rpm. Engine is rated 5500 RPM max. If I went to a 4-blade Renegade prop, would a 17" pitch be better? Boat is used mainly for fishing, cruising 16-22 knots average. Would the 17 be a better choice for maintaining plane at the lower end of the range? Not really interested in top speed, just comfortable cruising speed without beating myself or boat in choppy seas.
OutrageMan posted 09-06-2001 08:12 AM ET (US)
I have been through this a few times now with boats I have owned. To maintain the same RPM when going from a 3 to a 4 blade, you should go down 2" in pitch if the prop diameter is the same. You may even have to go down further if the prop is cupped.
smo posted 09-06-2001 10:02 AM ET (US)
I have seen just the opposite when going from a Mercury Mirage 17" 3 blade stainless to a Merc 4 blade stainless 17" Offshore prop. RPMS were across the board 200-300 higher at any given speed with the 4 blade than with the 3 blade. I ended up using a 19" four blade.
BillS
paulv posted 03-04-2004 05:59 PM ET (US)
I always have been told that a change of 1" would yield close to the same RPM, you will gain hole shot & cruising efficiency but loose a couple mph at the top end due to the pitch.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: 4 blade prop- 18' OR
acseatsri	posted 09-05-2001 09:49 PM ET (US) I'm trying to decide on a pitch for my Outrage. Currently running a 3-blade 14 1/2 x 19 pitch, WOT about 5100 rpm. Engine is rated 5500 RPM max. If I went to a 4-blade Renegade prop, would a 17" pitch be better? Boat is used mainly for fishing, cruising 16-22 knots average. Would the 17 be a better choice for maintaining plane at the lower end of the range? Not really interested in top speed, just comfortable cruising speed without beating myself or boat in choppy seas.
OutrageMan	posted 09-06-2001 08:12 AM ET (US) I have been through this a few times now with boats I have owned. To maintain the same RPM when going from a 3 to a 4 blade, you should go down 2" in pitch if the prop diameter is the same. You may even have to go down further if the prop is cupped.
smo	posted 09-06-2001 10:02 AM ET (US) I have seen just the opposite when going from a Mercury Mirage 17" 3 blade stainless to a Merc 4 blade stainless 17" Offshore prop. RPMS were across the board 200-300 higher at any given speed with the 4 blade than with the 3 blade. I ended up using a 19" four blade. BillS
paulv	posted 03-04-2004 05:59 PM ET (US) I always have been told that a change of 1" would yield close to the same RPM, you will gain hole shot & cruising efficiency but loose a couple mph at the top end due to the pitch.