Over-propped?

[jevery]

I have a Ranger Reata 1850 with Yamaha F150 turning a 21 P SS prop. WOT produces about 5400 rpm @ 50 mph with a light load of fuel and passengers. Manual recommends WOT upper half of 5000 ? 6000 K band with heaviest load expected. I would like better hole shot and from what I read here this motor is over-propped. I?m thinking 19 pitch Solas Titan or Titan HR or would a Michigan Wheel Avenger or Apollo be a better choice? Boat is a Fish & Ski and will be used for tubing and wakeboarding as well as fishing so low end pull will be important, but of course I don?t want a loss of top speed.
Thoughts?

 

[DJ]

Re: Over-propped?

Sounds to me like you are overpropped. However, the prop is only part of the story. Engine height and trim are factors too.

As a rule, one inch in pitch equals about 200 RPM, up or down.

 

[HighTrim]

Re: Over-propped?

As DJ stated, you need to use a prop 2" in pitch less than the prop that was used. Is your prop cupped? Since switching from an uncupped to a cupped propeller will reduce your RPM. The cupped propeller of the same pitch and diameter will typically reduce your RPM by approximately 200, or un cupping it will increase it by 200 in your case. Once your wide open throttle RPM falls within the recommended range of the engine manufacturer, you have a propeller that is suited correctly for your boat with respect to RPM. If you use your boat for fishing, cruising and skiing, one prop probably won't do all three things equally well. It is best in circumstances like this to have two propellers. One to accommodate one set of circumstances and the other to perform best under the different load. It could, in fact, be that more than one propeller would be suitable for your boat and motor combination depending on your usage. It is imperative, however, that the wide open throttle RPM fall within the range specified by your engine manufacturer