Interesting article on fuel economy and performance.

[sutor623]

I was trudging along and ran into this. Some of you may have already read it, but it was very interesting and informative to me. http://www.popularmechanics.com/outdoors/recreation/boating/1276841

 

[sutor623]

Re: Interesting article on fuel economy and performance.

This too. http://www.boatingmag.com/skills/calculating-fuel-consumption

 

[sutor623]

Re: Interesting article on fuel economy and performance.

So guys I was just wondering. Does can fuel usage in an outboard be calculated linearly? In other words, is fuel consumption directly proportional to engine RPMs?

 

[robert graham]

Re: Interesting article on fuel economy and performance.

Check: Outboard Motor Performance Bulletins, for info on GPH, GPM, MPG, etc. for various boat/motor rigs....I know my best fuel efficiency for my 90HP Yamaha 2 stroke shows right about 3500RPM's....I used to cruise slower at 2500 RPM's, but it just burns more gas per mile at the lower speed!

 

[tpenfield]

Re: Interesting article on fuel economy and performance.

So guys I was just wondering. Does can fuel usage in an outboard be calculated linearly? In other words, is fuel consumption directly proportional to engine RPMs?

No, it isn't. Just look at the fuel usage figures in the first article.

 

[sutor623]

Re: Interesting article on fuel economy and performance.

No, it isn't. Just look at the fuel usage figures in the first article.

Yeah I did that. So I guess it is just like finding the peak of torque in the powerband of an engine. There is a sweet spot in the RPM range for fuel economy. It is a constant battle between speed vs. time out on the water per tank of gas.

 

[sutor623]

Re: Interesting article on fuel economy and performance.

Check: Outboard Motor Performance Bulletins, for info on GPH, GPM, MPG, etc. for various boat/motor rigs....I know my best fuel efficiency for my 90HP Yamaha 2 stroke shows right about 3500RPM's....I used to cruise slower at 2500 RPM's, but it just burns more gas per mile at the lower speed!

What kind of GPH's are you burning up at 3500 vs. WOT?

 

[dingbat]

Re: Interesting article on fuel economy and performance.

The hull design detemines the best RPM for fuel usage.

 

[QC]

Re: Interesting article on fuel economy and performance.

Agree 100% ^^^^^^ marine fuel economy is most about hull and speed. Engine design matters as the test above shows, but ultimately the hull will determine what speed is best. Fixed, single, gear ratio means that RPM is a result, not a pursuit.

I am going to move this to non-Repair Outboard. It is specific to OBs, and important to note it is 11 years old.

 

[robert graham]

Re: Interesting article on fuel economy and performance.

What kind of GPH's are you burning up at 3500 vs. WOT?

The chart says 4.6GPH @ 3500RPM's, 9.2GPH @ 5600RPM's....but my MPG is 6.07 @ 3500RPM's and 4.62 @ 5600RPM's.....seems like the best MPG is just above plane around 3500RPM's. But we still find ourselves cruising about 2500RPM's @3.5GPH & 4.8 MPG, so old habits are hard to break, and the slower we go, the less of my wife's stuff ends up getting blown out of the boat!

 

[sutor623]

Re: Interesting article on fuel economy and performance.

The chart says 4.6GPH @ 3500RPM's, 9.2GPH @ 5600RPM's....but my MPG is 6.07 @ 3500RPM's and 4.62 @ 5600RPM's.....seems like the best MPG is just above plane around 3500RPM's. But we still find ourselves cruising about 2500RPM's @3.5GPH & 4.8 MPG, so old habits are hard to break, and the slower we go, the less of my wife's stuff ends up getting blown out of the boat!

Cool robert, thanks for the input. I have a '67 Merc 650 and havent really used her too much yet. I ran WOT for some long runs and fished all day on around 4-5 gallons of gas. I am thinking that on a regular fishing trip, as long as I put in close to where I want to fish, I can get away with 3-5 gallons of gas. Not too bad. I also have a little 4hp on the back that I use for putting around.

 

[sutor623]

Re: Interesting article on fuel economy and performance.

Also Robert, what type of GPH meter are you running? I am looking into buying one.

 

[robert graham]

Re: Interesting article on fuel economy and performance.

I don't have a GPH or fuel flow meter on my boat, but I just refer to the Outboard Performance Bulletin Chart to give myself a general idea of how much fuel required. I carry 24 gallons on my boat, so don't have to worry much about running out. We cruise the St.Johns River in Florida and marinas with gas docks are maybe 25 miles apart. Good Luck!

 

[sutor623]

Re: Interesting article on fuel economy and performance.

Cool thanks man. Im going to see if I can find the bulletin chart. Does Mercury have one of these, I know Yamaha does. Are there links to it on this site?

 

[robert graham]

Re: Interesting article on fuel economy and performance.

Mercury has a similar site called: Mercury Outboard Performance Bulletins, might give you some useful information. I believe that similar motors with similar HP and technology(2 stroke/4stroke), shoul have similar fuel flows, so the Yamaha site might help you some.

 

[sutor623]

Re: Interesting article on fuel economy and performance.

Cool thanks bro.

 

[sutor623]

Re: Interesting article on fuel economy and performance.

So robert I ended up finding a 16' aluminum starcraft, with a 50hp 2 stroke, and I am running a 65hp. Pretty close. From what I have read, I would say that I will burn around 3.5-5 GPH at cruising speed on my old '67. They werent too concerned about fuel consumption when fuel was 20c a gallon, or before "global warming". Motor is in suberb shape though. I have changed entire electrical system on her, and I am very happy with reliability and performance. Kinda hard to justify the price of a newer 4 stroke just to save 1 GPH or so at cruising speed.

 

[robert graham]

Re: Interesting article on fuel economy and performance.

The rule of thumb for 2 stroke motors is maximum fuel consumption at wide open throttle would be about 10% of the rated horsepower, or 5GPH for a 50HP....pretty close. For the new 4 strokes of course they do a bit better, but to justify the cost, weight and complexity, I'll just keep my old 90C Yamaha Premix!

 

[sutor623]

Re: Interesting article on fuel economy and performance.

For the new 4 strokes of course they do a bit better, but to justify the cost, weight and complexity, I'll just keep my old 90C Yamaha Premix!

Yeah forgot to mention that. It is incredible how much more the 4 strokes weigh.