Moderated Discussion Areas
ContinuousWave: Whaler Performance
4 blade prop- 18' OR
|Author||Topic: 4 blade prop- 18' OR|
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.
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.
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.
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.
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