24ft pontoon boat with 90 hp two stroke.

[Silver Eagle]

Usually when we go out for the day we usually just have the two of us so I usually run around 3400 rpms at 15 mph. Some times when I take off from an anchorage I like to kick it usually to 5,000 rpm's at 24 mph.. So what I really want to know is what's a good cruising speed at what rpms.with out hurting the motor .

 

[mla2ofus]

I have a 24' w/ a 90HP Force and usually run about 15 mph as this seems most economical on gas w/ a decent cruise speed.
Mike

 

[crb478]

If you are running within your recommended rpm range you will not be hurting the motor. You stated you have a 2 stroke motor. 2 strokes have fewer parts and you can get thousands of hours out of one that has been properly taken care of. They usually fail because of lack of oil or overheating issues due to blocked cooling passages. 4 strokes have more moving parts and require more maintenance, but can also last thousands of hours. Usually running at 3/4 throttle will get you the best fuel economy, but sometimes you just have to run it wide open. It is hard to over rev a 2 stroke anywhere near the WOT range

 

[mla2ofus]

It is hard to over rev a 2 stroke anywhere near the WOT range

I beg to differ. My force apparently doesn't have enough prop pitch as the engine tag says 5250 max RPM and it will go 6k easy in forward gear.
Mike

 

[ahicks]

Re: cruise speed, "best" is going to be a pretty subjective thing? It might be barely moving on a smaller inland lake, but when you need to cover some distance, I would say it would be the minimum speed to put/keep the boat "on top"? Maximum speed on minimum power?

Not going to get into the arguments regarding a pontoon's ability to plane. Call what it's doing whatever you want. What I'm talking about is going from the back end low, front end high attitude, to flat. Whatever speed that takes should be max miles per gallon for that boat's load and power (or pretty close?). Some might call that speed "best" cruise speed. Low teens?

 

[crb478]

I beg to differ. My force apparently doesn't have enough prop pitch as the engine tag says 5250 max RPM and it will go 6k easy in forward gear.
Mike

If your boat is not set up correctly you can over rev the motor. You need to address your prop issue for the health of your motor, it will not be geared right at any speed/rpm with the wrong prop

 

[Silver Eagle]

I have no prop problem,just wanted to know a safe rpm to run ,not wide open.For any long distance. I cruise around at 15 mph usually at 3400rpms. I'm not speeding just cruising.,But if I had too What's a good safe rpm to run without screwing up the motor.

 

[crb478]

If you are within your WOT limits with the prop you have run it at any speed you want and the motor will be fine.

 

[Silver Eagle]

I don't know my WOT That's the problem.

 

[cc350]

If motor is tagged at 5250 rpms max then 5250 would be your WOT limit. 2 strokes like the 3600 through 4800 rpm ranges.

 

[ahicks]

I don't know my WOT That's the problem.

If you'd like help with that question, need to know year, make and model info. Rated rpm varies. There's no "universal" number for all engines.

 

[crb478]

Most 2 strokes in the 90 hp range have a wot in the 5500-6000 rpm area. We would need the year, and make of your motor to know what is safe for you.

 

[Silver Eagle]

It's a 07 Mercury oil injected.with a three blade prop.

 

[crb478]

It looks like the range is 5250 to 5750, but you would need to verify this with Mercury given your specific motor.

 

[steelespike]

I beg to differ. My force apparently doesn't have enough prop pitch as the engine tag says 5250 max RPM and it will go 6k easy in forward gear.
Mike

Could be the prop also could be the tach not unusual for a tach to be off especially if it has some years under its belt.
What is the prop size , rpm and gps speed. What size and type of boat

 

[Silver Eagle]

The GPS and the speedometer are with in one half off.Tack is certified good.. I'm not having any problems with the prop or any part of the motor .I just wanted to know what I can run at with out hurting the motor.Also try reading each entry from the start.

 

[steelespike]

Disregard my reference to planing substitute speeds just before beyond ideal speed.
My info indicates 2005 on 90 hp rpm range is 5000 to 5500.
If your within that range at wot you can run at any speed you like.
I think it is pretty obvious that if you run wot all the time it will stress the motor more than say 4000.
I think it is also obvious that as rpm goes up stress goes up.
About the only speed that stresses the motor unnecessarily is a speed that holds the boat at a speed just before planing.
Throttle setting will be higher just before planing than at speeds just on plane.Pontoons not included as they don't truly plane.
But do have ideal cruising speeds.
The ideal cruising speed; a reasonable speed with best mpg would be somewhere from just on plane to about 1000 rpm higher.
Trial and error or a flow meter is about the only way to find an ideal cruising speed.
I think that the ideal cruising speed would put the least stress on the motor seeing as it produces the most speed with the least fuel.

 

[Silver Eagle]

Plaining isn't in my plans..I'm only doing 15 mph usually and I'm in the Chesapecke Bay.The water isn't like lake water.Lot's of rolling swells.And with the bigger boats making there own wakes not much time to plain

 

[ahicks]

Unless you're reaallly loaded down, at 15mph, I'd be surprised if you were not planing. If not, your boat would be riding bow high, stern low, and creating a huge wake.... On plane, the boat is likely very near level.

 

[Silver Eagle]

I have a round shaped leveler next to my console It numbered from zero to30 There's a little steel ball in it and it tells me if the boat it traveling level.The ball can go forward or backwards. Most of the time it's just past 3 to 4. When I had my bow rider with the 5.7 I/O it was usually at 5 to7.