Wondering about my Motor and performance

[chevyman_1979]

I just recently purchased a 1996 24 ft Weeres 240 Sundeck with a 75 HP 2 stroke Merc. I am not sure on the year of the motor, or what the best operating range of the rpms since I did not get a manual with it. The Serial Number is 0G271141 and I have a prop that says 48 77342A45 15P so I know it is a 15 Pitch prop but not sure on the size. at WOT i am getting about 3500 RPM with 2 adults and 3 kids and my GPS MPH ranges from 14 to 15. when I add a couple more adults I am only getting 3000 RPMs or less. I am wondering if that sounds right or if I should be getting a new prop or getting the motor looked at. It runs great but not sure if there could still be something wrong. I always thought a motor should run around 5000 RPM any help would be greatly appreciated. Thanks

[BobG]

15 pitch seems a bit steep for a 75 HP.
I'm running a 13 pitch on my 115 - which only puts out 95 HP at my elevation.
I'm guessing that you would do better with a 13 or even an 11.

[LocoCoco]

WOT should be somewhere around 5000-6000 rpm. And that prop sounds to me a bit big for that motor on that boat. I'd want to try out a 10p to 13p.



LC.

[chevyman_1979]

what size circumference do I need? Still the 13 3/4? or 13 1/2? or do I go smaller with that too

[LocoCoco]

Pretty sure you just have to worry about pitch. The diameter gets sized accordingly.


LC.

[dakotamedic]

I have a 1992 merc 75 hp 2 stroke. Mine had a 14x 13p on it when i got it, seemed ok, but the WOT rpms were about 5000. I needed a new prop after a rock incident, and was told by a marina repair guy that a 14x 11p would be a little better for WOT rpms. It did go up to about 5400 WOT. Speed is about 20 on my 24foot crestliner withthis setup.

[ROLAND]

chevyman.... just to give you something to compare yours to.... I have a 75 horse 4 stroke on my 20 foot toon... I'm running a 13 P Prop and running wide open I get just a hair under 6000 rpm's, and under perfect conditions, around 24 mph with 2 people and our gear on board.

[kryptonite]

I'm running a 75hp 4 stroke with heavy loads most of the time. I run a 14x11p. I have a spare 13.75 x 13p.

[screwball]

More comparisons....

I 'ate' my 13.75 X 13 on a rock, so I thought this is the opportunity to get a mile per hour or 4. Had an old 13.5 X 15 stainless for my old Force motor. It fit, so I tried it. HORRIBLE! at about 4000 rpm the slippage was real bad. Could only get about 14mph out of it. Sooo, bought an aluminum 17 pitch. Running around 22 mph (GPS) BUT I can only get 4200rpm. I'm guessing an aluminum 15 pitch would do it. So the 13 I ate will go to the Prop Dr. and get re-pitched to a 15. At WOT the original 13 would / could over speed.

[WaltF]

Trial n error.

Idea is to be able to hit redline with only a couple peeps on board.
Anything less then that and youre always running in a bogged state, which isnt great for the motor.

Find out what redline is for your motor, throw an 11 on there, same dia, and see what cha get....