Prop Advice

dazzadazza Member Posts: 2 ✭
in Rinker Sport Boat Forum

Hi all,  Just fitted a new 4 blade 21P prop to my 186 4.3L. (Original was three blade 23P)

The issue I have is that in everything I have read when u drop the pitch size your RMP should drop as well.  However, I am experiencing the opposite.  My RMP has increased from 4800 to 5200.  At the same time boat speed was dropped by 6-8km/h.  Is this normal?  Or is something wrong?  Or do I just enjoy the change and watch the RMP to stay under WOT.  The boat gets out of the hole better and appears to plane at a lower speed.  Thanks

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Answers

  • pault1216pault1216 Member Posts: 206 ✭✭✭
    When you reduce the pitch, rpm goes UP, typically 200-300 RPM per inch. Adding a blade factors in also. Might consider the tach accuracy also. I have a 4.3l in my 190SE Mariah and the rev limiter cuts in at 4850-4900 rpm if I am not mistaken. If you are looking for speed keep the 23" pitch although I would think your hole shot my be on the slow side. Good luck.
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  • Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭

    Same style of prop: pitch down- rpm up, speed down, hole shot/planning time better.

    However, if you change the rake, diameter or number of blades that changes everything.

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