RPM Range

[Chemdawg]

Hello everyone. Finally got to take my boat out for the first time yesterday for the year. Since this is my first boat, it really creeps me out to get the RPM's up so high. I keep thinking in terms of a car. But I realize that a boat motor is different. So here is my info.

1987 Arrow Glass Carisma 175. 3.0L Mercruiser with Alpha 1 drive. Prop is a 19 pitch factory.

I was at about 30 mph at like 4400 RPM. I had myself, my wife, and two kids on the boat with me. So you figure that's about an extra 500 lbs. I felt like I had a bit more I could go on the throttle lever, but I didn't want to go to high. What is the max safe RPM level you can run this motor at? I thought I'd get a bit more than 30 out of this boat. But I'm not sure.

Thanks in advance.

Pat

 

[bspeth]

Re: RPM Range

Its in your fsm

 

[ziggy]

Re: RPM Range

wot spec is 4200-4600 per s/m 10.
imho, yer sittin about right. loose the weight and your gonna see a little more rpm likely.

fwiw. my wot spec is 3900-4300. i shoot for 4300. i don't do wot very much. but i think i'm propped right since i can achive it. i've had mine up to 4400 at one point. pretty wound out, but still works. best i know, it's never been rebuilt either. most of my time spent on the lake is at 3k and below. cruisein, not wot.

 

[UncleWillie]

Re: RPM Range

Unless there is a specific reason not to; Operating at Wide Open Throttle (WOT) for extended periods is not out of line in a boat.
The proper propeller is selected to allow the engine to run just under the maximum design RPM at WOT without any issues.
A prop that slows the engine down is worse, as it raises the pressure and temperature in the engine.
Modern engines are spec'd closer to 5000rpm and many OBs are closer to 6000.
Many Boater on calmer lakes and rivers may run at WOT for an hour or more.

 

[tinkerguy70]

Re: RPM Range

Hello everyone. Finally got to take my boat out for the first time yesterday for the year. Since this is my first boat, it really creeps me out to get the RPM's up so high. I keep thinking in terms of a car. But I realize that a boat motor is different. So here is my info.

1987 Arrow Glass Carisma 175. 3.0L Mercruiser with Alpha 1 drive. Prop is a 19 pitch factory.

I was at about 30 mph at like 4400 RPM. I had myself, my wife, and two kids on the boat with me. So you figure that's about an extra 500 lbs. I felt like I had a bit more I could go on the throttle lever, but I didn't want to go to high. What is the max safe RPM level you can run this motor at? I thought I'd get a bit more than 30 out of this boat. But I'm not sure.

Thanks in advance.

Pat

I'm running a similar boat with the same prop. You're right on the money, as far as I can tell. Don't worry about running at WOT too much, once you start buying fuel for it, you'll stop doing that.

 

[Chemdawg]

Re: RPM Range

Thanks for those answers. I know that I have a problem with my engine running a bit rich right now. Needs some tuning. But it's getting there. Just figured maybe I had a problem elsewhere.

Thanks again!
Pat

 

[Alumarine]

Re: RPM Range

If you have more throttle left you might want to try a 21 pitch prop.

 

[Starcraft5834]

Re: RPM Range

Chem. I've got a 1987 3.0 140hp too. Im running a 15x16 Michigan Wheel 4 blade. its a 20ft cuddy, Im getting 33gps at 4400-4500 rpm.. I'd say your in good shape, as mentioned, if you have throttle left..go up in pitch +1...have fun