Same pitch and diameter, lost 1000rpms

[Sea Rider]

Check wot rpm with you alone on flat calm no wind water cond. Check at which trottle setting engines achieves max wot rpm factory stated for that engine and how much more throttle is left. So rule of thumb doesn't work for your application, that's 425 + revs per pitch decrease, double than rule of thumb.

Usually you need to "buy" at least 2 other props after testing original one, second will tell your real world rpm gain per pitch decrease. A third will dial best one for your current application if second doesn't satisfies what you're looking for, that's while maintaining same diam and playing with different pitch sizes. Dialing best prop is same as winning a Lotto.

Happy Boating

 

[Wwohl]

Okay some follow-up...

Original OEM Yammy prop 13.25x17 - 5500 RPMs, 24mph, 42% slip.
Solas rubex 13.3x17 - 4500 RPMs, 24mph, 29% slip.
Solas rubex 13.8x13 - 6200 RPMs, 22mph, 38% slip.

Just installed a Solas rubex 13.5 x 15 - 4900 RPMs, 25mph, 24% slip.

Well SOB... the 15inch prop is very efficient it seems - running at 24% slip. The problem is, im below my factory recommended 5000-6000 RPM range. Also getting a little torque in the steering now (hydro) and pulling right at WOT slightly.

If the 13 inch had less slip my RPMs would have been fine..

Im lost.... and tired... and ive spent way too much time and money on this thing..

Guidance?

 

[batman99]

If "sweet spot" is between 3-blade 13' and 3-blade 15', then perhaps a 4-blade 13' (which feels 1 pitch higher with more grip than a 3-blade) would be perfect?

If wondering, my Bowrider boat loves 4-blades better than 3-blades. Your boat might like 4 blades better as well.