What constitutes "over-propped"

[jfbetz]

I'm wondering what level of decrease in WOT rpm would constitute my motors being over-propped. Got a pair of Yamaha 250's (replacing last years225's) on a 25' BW Temptation. Yami specs say 4,500 - 5,500 rpm range. I'm swinging a 23 pitch prop (up from a 21 pitch on the 225's) but have not had it in the water yet. 21 pitch produced just about 5,400 rpm. With 25 more hp, and the engines set up a notch on the transom, I'm hoping the 23 is the right prop, however if RPM's decrease, at what level would it be considered over-propped?

 

[Silvertip]

Re: What constitutes "over-propped"

Overpropped means the engine(s) cannot reach the manufacturers maximum recommended wide open throttle rpm range (4500 - 5500 rpm in your case). So running wide open, if the engines can't reach 4500 rpm you are way over propped. It is always best to shoot for the upper end of the range for best performance. If the boat is propped for an average load and can only reach the lower end of the band, loaded heavy the engines will really struggle.