question about prop pitch. not like the others....

[cjones50]

ok guys, hopefully i can get some help. i have owned the boat for less than a month, and as i was told i would need a spare prop. well without fail i tore up the only one i had yesterday. i have a mercruiser 3.0 with alpha one. it had a 14.5x19 on it. heres the question, if i move up to a 14.25x21 will my engine have too much load on it as i accelerate? because i've heard that is just as bad for the engine as over revving. i'm not worried about the hole shot because we only do tubing and dont need the fast pick-up like skiing or boarding. what makes me want to step up is even not at wot with 4people in the boat i am up at 4600-4800 rpm. thanks for the help guys, i'm tryin to go and get one tomorrow, so hopfully you/re all online.

p.s-yes i'm having the 19p repaired so i dont loose another half day on the water!

 

[Silvertip]

Re: question about prop pitch. not like the others....

You need to understand that it is the prop that determines how your boat performs and it also limits over reving or under reving. Your engine is in the correct rpm band with the existing prop. If you go to a 21, you will lower rpm by about 400 rpm but understand that you also affect both low speed and high speed performance as well as everything in between. Why? Because too much pitch is like starting out with a stick shift car in high gear. So you ruin hole shot on the low end and you cause higher fuel consumption because you need more throttle opening on the high end to compensate for the increased pitch. You have a throttle lever. If you don't like seeing 4600 rpm pull back on the throttle. That's what it's for. Changing pitch because of that does indeed affect engine capability. If a prop is wrong it is wrong across the entire rpm band - not just at various points within that band. A prop should always be selected to put the observed WOT engine rpm within the manufacturers recommended RPM band with what you consider an average load.

 

[hwsiii]

Re: question about prop pitch. not like the others....

Silvertip, that was an excellent explanation of what PITCH does to and for a boat, it explains it succinctly. EXCELLENT


H