Max prop pitch for 30L Merc Cruiser

"I run a 2000 Merc Cruiser 135

"I run a 2000 Merc Cruiser 135 hp 3.0L on a Larson 180 normally with a 14.5 dia 19" pitch prop. I get about 43 mph at WOT. Not sure what the RPM is since the tack under reads. It shows 3200 but last year a tech put a meter on the engine and it runs at 4800.

I recently tried a 23" pitch prop and only picked up about 3 mph at top end and indiacted rpm dropped by about 400. I can hear the significant change in rpm too.

I'm wondering what the max pitch I can run on this motor without causing problems by lowering the rpm so much. I'd like to see what kind of speed is possible from it, understanding that I need to switch the prop when we use it for skiing to get out of the hole. Also interested to know what percentage of fuel efficiency I pick up with the higher pitch prop at cruise.

Also, is there an adjustment that I can make on the indicated rpm at the gauge? It's under read since brand new.

Thanks.

BTW the prop calculator from the April 26, 2007 post was pretty much right on for the test conditions I ran last weekend. Thanks."

"That engine needs to run at i

"That engine needs to run at it's WOT range which is 4400 to 4800 RPM's. If it were me I would stick with the 19 pitch. The 21 Pitch will bring your RPM's down approx 250 RPM's or so. Larson's are heavy boats (but dan good ones!) and the 19 Pitch serves that rig well.

I would say that 23 Pitch wheel is too much prop for that 3.0L. You are at the very bottom of your RPM range at 4400 w/ a 23.

I have a Stingray 180LS w/ a 3.0L and run a 17 Pitch stainless prop.

Take care,

T."

"Fuel Economy and WOT don'

"Fuel Economy and WOT don't usually appear in the same sentance.

If you want fuel economy, the larger prop will help, but not at WOT. At a moderate cruising speed (20-25 knots) you'll realize some efficiency.
Trim tabs and maybe a hydrofoil will help too. I wouldn't expect miracles though.

If you want to go faster, you need more engine or less boat.

Boat size, engine power, gear ratio, and prop size
comprise a delicate balancing act. The folks that put the whole package together usually aren't too far off the mark. Some adjustments, based on intended use, can be made. Probably not what you wanted to hear, but what you get from the factory is what the design folks thought would work best."

"jeff, for what its worth, i h

"jeff, for what its worth, i have a marada mx1 18 ft bowrider with the 3.0lx. i run a 23 pitch and my wot is about 4600 with just me and full gas. i get about 43mph. cruise is at 25mph at 3100 rpm. hope this helps."

"Jeff;
I think everything tha

"Jeff;
I think everything that has been said above is right on target. Your engine is telling you it is maxxed out at 4800 RPM @ 43 MPH with the 19" pitch prop. I think you will lose one way or the other by changing anything.
You might consider dropping in a 220 hp V-6 which I think will fit right in your engine bay. That should get you into the mid 50's MPH. The downside of course is you will burn more gas anytime your right hand gets heavy; but hey, that's what boats are for, right?
About the tach, are you sure the selector on the back is set correctly? It sounds to me like it may be set for a six cylinder because it is reading about 67 % of what it should be. You might want to check this out.
Good luck.
Rod"