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Gernby

Most economical / efficient cruising speed?

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Gernby

Now that gas prices are so friggin' high, I really want to cut back on waste while just cruising from one side of the lake to the other. Obviously, when towing a skier, I'm going to go at whatever speed they want, but I also do quite a bit of cruising. Does anyone have any suggestions for optimum cruising speed or RPM? I have a '98 Sunsetter LX with the 325 Monsoon and an OJ 13X11.5 prop. My gut feeling is that 25 MPH (~2700 RPMs) would be close to optimum, but that's just a wild guess. What are your thoughts?

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bigD

Just fast enough to get on plane.

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RTS

I would guess that theoretically, your best MPG would be right above the planing speed of your boat. I saw the boat test result for my boat (an '02 Sunsetter LXi with the 325 Monsoon...pretty close to yours) and one bit of data I remember was 30+ Gallons per hour at WOT...so maybe avoid that.

Edited by rts

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Bill_AirJunky

My truck seems to get the best MPG when the engine is turning around 2000 - 2300 RPM. So I would assume that your boat engine would be getting the best GPH around the same RPM, while the boat is on plane.

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vette-ski

Being on plane is the key. That's a huge drag factor that goes away and would make it hard to compare to a road vehicle for rpm.

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Gernby

Thanks for the replies! I guess I need to adjust my logic a bit since I'm used to smaller engines where peak efficiency is higher in the RPM range. Would it matter much where the weight is distributed? Would it be better for us to keep all our gear and passengers at the rear, middle, or front?

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chadwick02

this was talked about a week or two ago. I book marked it on my home computer, but I dont have it here at work. Someone posted a great chart with monsoon fuel consumption in gallons per hour VS RPM. I cant remember what the best range was however.

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Bill_AirJunky
this was talked about a week or two ago. I book marked it on my home computer, but I dont have it here at work. Someone posted a great chart with monsoon fuel consumption in gallons per hour VS RPM. I cant remember what the best range was however.

Heres the thread.

And the bottom line, thanks to electricjohn.....

1000 rpm....6.9mph...1.5gph...4.6mpg...170 mile range...75db...1*run angle

1500 rpm....9.2mph...2.8gph...3.3mpg...121 mile range...94db...4*run angle

2000rpm...17.1mph...4.2gph...4.1mpg...150 mile range...92db...5*run angle

2500rpm...24.6mph...6.2gph...4.0mpg...146 mile range...83db...3*run angle

3000rpm...30.2mph...8.1gph...3.7mpg...138 mile range...88db...2*run angle

3500rpm...35.4mph..10.8gph...3.3mpg...121 mile range...82db..2*run angle

4000rpm...39.2mph..14.2gph...2.8mpg...102 mile range...88db...2*run angle

4500rpm...43.0mph..18.7gph...2.3mpg....85 mile range...86db...2*run angle

4900rpm...45.5mph..23.9gph...1.9mpg...70 mile range...91db....2* run angle

I would think you'd definitely need to drain all the ballast for max GPH.

Edited by Bill_AirJunky

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VinRLX
Just fast enough to get on plane.

Nope. 2500-3000 RPM for a DD and 3000-3500 for a VD. YMMV (YMMV. Get it? Your mileage may vary? Sometimes I crack myself up)

However, with this being the second thread on this in as many weeks, you have to wonder. . .

The difference in fuel economy changes, hypothecially, from say 1.9 MPG to 2.3 MPG based on the RPM you run. Based on the distance you are traveling, how much difference does it make?

Or, from a different perspective, lets say you go through 200 gallons of fuel per season. How many gallons, more or less, would 500 RPM make during your non-skiing runs (assuming the ski/board use is a constant)?

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Gernby

Thanks for posting the link to that thread! I used the "Search" feature before creating this thread, but it wouldn't let me use 3 character parameters (GPH, MPG, RPM). What an odd limitation for an engine related forum.

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Gernby
Just fast enough to get on plane.

Nope. 2500-3000 RPM for a DD and 3000-3500 for a VD. YMMV (YMMV. Get it? Your mileage may vary? Sometimes I crack myself up)

However, with this being the second thread on this in as many weeks, you have to wonder. . .

The difference in fuel economy changes, hypothecially, from say 1.9 MPG to 2.3 MPG based on the RPM you run. Based on the distance you are traveling, how much difference does it make?

Or, from a different perspective, lets say you go through 200 gallons of fuel per season. How many gallons, more or less, would 500 RPM make during your non-skiing runs (assuming the ski/board use is a constant)?

I understand your point that fighting for a 20% improvement in fuel economy has limitted value, but there is more to it than just money. We keep our boat in a slip, so getting gas requires going to the marina, and waiting for someone to come unlock the pump. If I can avoid doing that even once per season by cruising at a better speed while looking for the "right cove", it would be worth it.

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VinRLX

Here are a few more charts to add fuel to the fire.

post-30-1213036117_thumb.jpg

post-30-1213036101_thumb.jpg

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VinRLX

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Bill_AirJunky
Thanks for posting the link to that thread! I used the "Search" feature before creating this thread, but it wouldn't let me use 3 character parameters (GPH, MPG, RPM). What an odd limitation for an engine related forum.

Yea, I searched for "monsoon efficiency" & nailed it. Gotta get creative with that 3 letter limit in place.

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jgouveia3

since every time you go out, you are probably going to be differently weighted (gear, gas, ballast, etc), the only way you are really going to be able to tell is if you have a fuel management system on your boat (like i do on my Outboard). Depending on wave condition, boat load (i.e. pds of fish - which in my case almost always seems to be 0), trim angle, trim tab position, my most efficient running speed is NOT always the same RPM. It is probably more consistent on our ski/wakeboard boats because we are usually on lakes, but weighting does make a big difference.

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Gernby

I agree that it will be different for every boat / day / load, but it looks like 20-25 MPH would be a pretty safe bet based on all the charts above.

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