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First thing I tried, fixed the problem!

F

floatin radio

Regular Contributor
Merc 3.0, alpha 1, 91 searay br170
Was out this weekend crusin on lake, 19p prop, was only getting 4000 WOT@ 25 mph, two adult, full 22 gallon tank. Something just wasn't right. I was pulling my son tubing and it was just a dog. I changed to a 17 pitch prop, instant success! 4400 rpm@ 33 mph, same 3 people, full tank. No issues at all pulling tube.
Prop hub slip on 19p prop? Could it be that simple?
 
No

The way a boat achieves it max rpm's is through prop pitch/diameter change.

Typical is for one pitch change you gain or loose ~ 300 rpms.

example.

19 pitch, 1 person, 1/2 tank of fuel, any engine, full throttle and trimmed out to max before cavitation.

if engine only reaches 4000 to 4200 rpms. go DOWN one pitch to 17P

this will make the boat come out of the water quicker and it will give you a max RPM of ~ 4300 to 4500 rpms.

Reverse for over rpms.

With your boat, your configuration, if you go out alone, same fuel, NO additional people. full throttle and trimmed out your boat will most likely achive 4500-4700 rpms now.

Also it is not uncommon to have a couple of different prop pitch's for different uses.

If you have an outdrive boat, normal use would besay 19 pitch. But with poepl and extra wieght and pulling a tuibe or skier it is common practice to go down a pitch to get the hole shot which seems like better pulling power.

It may be possible that you boat requires a 17 for normal use........typical pitch range (engineered into all small pleasure boats) is 17 -21 pitch.

Hull, power, and several other boat configurations all play a role in what prop works best.......
 
the recommended rpm for the 3.0l engines is right at 4400 to 4800 so you could even play with the prop a little more if you would like to get more top end out of it
 
Thanks guys, I read up on prop pitch. I think I have a grip on it now. 17p works well, I would like to try a 15p three blade and a 19 p four blade. I added trim tabs a couple years ago, great investment! I have no problems planing out with the 17 or the 19.
 
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