prop question

[wswaneyw]

Am I safe in assuming that the lower the pitch prop the higher the speed??? I have a 19 pitch on my chrysler 120 and when i put it to WOT we are off with the horses. It planes really really fast. I purchased a 15 pitch a few days ago and have yet to try it. I can run around 42-43 with the 19. Is this 15 going to give me a few more mph and just as good as a hole shot? Thanks Wayne

 

[JB]

Re: prop question

No, Wayne.<br /><br />You have it backward. The higher pitch travels farther than the lower pitch for one revolution, ignoring slip.<br /><br />Think of the 19" as high gear and the 15" as second gear.<br /><br />Ordinarily your car would go faster in high than in second, BUT. . . on a steep hill or with a heavy load it would probably go faster in second.<br /><br />Prop selection for a boat is a matter of finding the right "gear" to allow the engine to use all of it's power without bogging down or over-revving. Without a tachometer and knowledge of the engine's proper operating rpm you are just wandering around in the dark.<br /><br />What rpm are you turning at your 42-43 top speed?<br /><br />The chances are that you are going to feel like you are stuck in second with the 15". Engine screaming near self destruction and less speed.<br /><br />Do a search on prop selection. There is a lot to learn.<br /><br />Good luck.

 

[boating brad]

Re: prop question

no more speed (maybe less), little better holeshot. higher wot rpm, the 15 pitch will give you 800 more rpm, which can help alot if you are presently lugging the motor, or if you carry alot of people on the boat, pull a skier, etc.<br />the whole idea is to not lug the motor, if you lug the motor it can fail prematurely. <br />jb is a fast typer, and 100% right. definitly on that tach issue

 

[wswaneyw]

Re: prop question

I am right around 5000 rpms with the 19. Operating range is right around 5100. I think i will leave the 19 on when there is going to be just a couple of us in the boat(wife and 2 kids) and switch if there are 4 adults in the boat. I think adding 800 rpms to 5000 would make for a large explosion on the back of my boat.<br /><br />If all else fails,,, at least i will have a spare prop in the boat in case the other takes a beating.