Engine Rpm vs. Prop pitch

[Andrew Leigh]

Hi,<br /><br />I don't know where to post this one but here goes with some questions.<br /><br />a) Am I correct in assuming that if I get 5400 Rpm out of my 1998 115hp V4 Evinrude with a 17" prop that I am correctly "propped"?<br /><br />b) If holeshot performance is not important would it not extend the engine life were I to go for a 19" prop and consequently reducing the rpm?<br /><br />b) Would the 19" prop give better top speed or would I run out of torque owing to the fact that I will running lower down on the torque curve?<br /><br />Cheers<br />Andrew

 

[JB]

Re: Engine Rpm vs. Prop pitch

Good questions, Andrew, and some that many boaters don't understand.<br /><br />1. Yes. If you are getting 5400 at WOT you are probably using a correct pitch for your rig.<br /><br />2. No. Going to a longer pitch will probably not allow your engine into its best operating range and shorten, not lengthen its life. <br /><br />3. The 19" prop would probably reduce your top speed as well as your WOT rpm.<br /><br />Your engine would have to work harder to reach WOT rpm with the 19" prop, resulting in greater strain on your engine, not less, and it may not have enough torque to reach the same top speed.<br /><br />Depending on how you use your boat, some might even recommend a shorter pitch than the 17", looking for a WOT rpm closer to 6,000rpm.<br /><br />I am going to move this to General Outboard, where propping questions get more attention.<br /><br />Good luck.