Fuel Consumption of Yamaha 90-HP Classic Two-cycle

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  Fuel Consumption of Yamaha 90-HP Classic Two-cycle

search | FAQ | profile | register | author help

Author Topic:   Fuel Consumption of Yamaha 90-HP Classic Two-cycle

Johnny50 posted 04-21-2009 05:16 PM ET (US)
What MPG can be expected from a 2007 90-HP Yamaha outboard on Montauk 17? If anyone has this set-up or any helpful info I would appreciate it. Thanks.
jimh posted 04-21-2009 06:53 PM ET (US)
At wide open the motor will burn about 8 to 9-GPH.
You can figure the fuel burn of a classic carburetor two-cycle motor using a brake specific fuel consumption (BSFC) about 0.55-lbs/HP-hour at best.
90-HP x 0.55-lbs/HP-hour X 1 hour = 49.5-lbs
Gasoline is usually about 6.25-lbs/gallon, so in terms of volume.
49.5-lbs X 1-gallon/6.25-lbs = 7.92 gallons.
We don't know anything about your particular boat, but a Montauk with a 90-HP Yamaha is predicted at 45-MPH. Cf.:
http://continuouswave.com/whaler/reference/16-17/repower.html
If your boat runs as predicted, your miles-per-gallon will be
45-miles/1-hour x 1-hour/7.92-gallons = 5.6-MPG
This is probably the absolute best you could ever get. Expect your boat to show somewhat lower results.
The BSFC of an engine varies with the percentage of throttle and other factors, so at speeds less than wide open the BSFC may be worse, or then again might be slightly better.
The biggest influence is your propeller set up. Nothing is more influential in a boat's performance. Poor propeller selection will ruin your fuel economy.
The best answer is to go measure it. And I don't mean measure it with some seat of the pants eyeball. Really monitor the precise amount of fuel used and the exact distance travelled. It is not had with a chartplotter. Use a full tank and carefully refill to the exact level you started with. You get good data.
jimh posted 04-21-2009 06:59 PM ET (US)
"If anyone has this set-up or any helpful info I would appreciate it"
There is no topic which has been more thoroughly discussed than re-powering and set up of a MONTAUK on this website. In the archives there are probably 4,000 articles or comments on this topic. You are welcome to read them.
There is a very brief index to them given at
http://continuouswave.com/whaler/reference/16-17/repower.html
Use the SEARCH function to find more. Searching is very efficient and finds anything on this website.
You might want to read the REFERENCE articles on the 17-foot hull, too.
http://continuouswave.com/whaler/reference/16-17/
Then there is a whole section of the REFERENCE section on PERFORMANCE:
http://continuouswave.com/whaler/reference/
Feel free to use the PROPELLER CALCULATOR:
http://continuouswave.com/cgi-bin/propcalc.pl
or CROUCH's CALCULATOR:
http://continuouswave.com/cgi-bin/crouchcalc.pl
Peter posted 04-21-2009 07:33 PM ET (US)
The Montauk performance with a Yamaha 90 2-stroke will be quite similar to the performance in this report www.yamaha-motor.com/assets/products/otb/bulletins/ bulletin_otb_2StrokePerf_HPMidPort_90hp_01184-ALM-Z.pdf
Johnny50 posted 04-21-2009 09:00 PM ET (US)
thanks for all the info
jimh posted 04-21-2009 10:55 PM ET (US)
Based on Yamaha's own data on the fuel consumption rate, it looks like the BSFC of the Yamaha 90-HP at wide-open throttle is around 0.62-lbs/HP-hour. That is higher than I thought, thus you'll have to round down my estimates of MPG about ten percent.
Tohsgib posted 04-22-2009 11:38 AM ET (US)
My 90 Yamaha on my 89 Montauk with 13x19 Yamaha SS prop would run 41.5mph on avg at WOT. At cruise(38-3900) and high 20's she would burn roughly 4.5gph or roughly 6mpg. Great combo for that boat and being a conventional 2 smoke, not bad economy. The engine however is a tad weak in the HP...more like 80hp compared to an OMC or Merc 90hp. Maybe that is why the economy is better.
Johnny50 posted 04-22-2009 10:24 PM ET (US)
tohsgib, what size fuel tank do you have on yours? Single tank or more? thanks
L H G posted 04-22-2009 11:25 PM ET (US)
[Changed TOPIC to the fuel economy of another motor. Please begin a new discussion to change the topic to the fuel economy of another motor.]
Tohsgib posted 04-23-2009 11:09 AM ET (US)
I had a Pate 27 but when I repowered it with a Suzuki 70 4stroke the gas would bad so I got rid of it(actually still in my shed). Depends on how far you go but a single 6 is not gonna cut it at 4.5GPH at cruise. I would go with a Moeller 26 under the RPS.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: Fuel Consumption of Yamaha 90-HP Classic Two-cycle
Johnny50	posted 04-21-2009 05:16 PM ET (US) What MPG can be expected from a 2007 90-HP Yamaha outboard on Montauk 17? If anyone has this set-up or any helpful info I would appreciate it. Thanks.
jimh	posted 04-21-2009 06:53 PM ET (US) At wide open the motor will burn about 8 to 9-GPH. You can figure the fuel burn of a classic carburetor two-cycle motor using a brake specific fuel consumption (BSFC) about 0.55-lbs/HP-hour at best. 90-HP x 0.55-lbs/HP-hour X 1 hour = 49.5-lbs Gasoline is usually about 6.25-lbs/gallon, so in terms of volume. 49.5-lbs X 1-gallon/6.25-lbs = 7.92 gallons. We don't know anything about your particular boat, but a Montauk with a 90-HP Yamaha is predicted at 45-MPH. Cf.: http://continuouswave.com/whaler/reference/16-17/repower.html If your boat runs as predicted, your miles-per-gallon will be 45-miles/1-hour x 1-hour/7.92-gallons = 5.6-MPG This is probably the absolute best you could ever get. Expect your boat to show somewhat lower results. The BSFC of an engine varies with the percentage of throttle and other factors, so at speeds less than wide open the BSFC may be worse, or then again might be slightly better. The biggest influence is your propeller set up. Nothing is more influential in a boat's performance. Poor propeller selection will ruin your fuel economy. The best answer is to go measure it. And I don't mean measure it with some seat of the pants eyeball. Really monitor the precise amount of fuel used and the exact distance travelled. It is not had with a chartplotter. Use a full tank and carefully refill to the exact level you started with. You get good data.
jimh	posted 04-21-2009 06:59 PM ET (US) "If anyone has this set-up or any helpful info I would appreciate it" There is no topic which has been more thoroughly discussed than re-powering and set up of a MONTAUK on this website. In the archives there are probably 4,000 articles or comments on this topic. You are welcome to read them. There is a very brief index to them given at http://continuouswave.com/whaler/reference/16-17/repower.html Use the SEARCH function to find more. Searching is very efficient and finds anything on this website. You might want to read the REFERENCE articles on the 17-foot hull, too. http://continuouswave.com/whaler/reference/16-17/ Then there is a whole section of the REFERENCE section on PERFORMANCE: http://continuouswave.com/whaler/reference/ Feel free to use the PROPELLER CALCULATOR: http://continuouswave.com/cgi-bin/propcalc.pl or CROUCH's CALCULATOR: http://continuouswave.com/cgi-bin/crouchcalc.pl
Peter	posted 04-21-2009 07:33 PM ET (US) The Montauk performance with a Yamaha 90 2-stroke will be quite similar to the performance in this report www.yamaha-motor.com/assets/products/otb/bulletins/ bulletin_otb_2StrokePerf_HPMidPort_90hp_01184-ALM-Z.pdf
Johnny50	posted 04-21-2009 09:00 PM ET (US) thanks for all the info
jimh	posted 04-21-2009 10:55 PM ET (US) Based on Yamaha's own data on the fuel consumption rate, it looks like the BSFC of the Yamaha 90-HP at wide-open throttle is around 0.62-lbs/HP-hour. That is higher than I thought, thus you'll have to round down my estimates of MPG about ten percent.
Tohsgib	posted 04-22-2009 11:38 AM ET (US) My 90 Yamaha on my 89 Montauk with 13x19 Yamaha SS prop would run 41.5mph on avg at WOT. At cruise(38-3900) and high 20's she would burn roughly 4.5gph or roughly 6mpg. Great combo for that boat and being a conventional 2 smoke, not bad economy. The engine however is a tad weak in the HP...more like 80hp compared to an OMC or Merc 90hp. Maybe that is why the economy is better.
Johnny50	posted 04-22-2009 10:24 PM ET (US) tohsgib, what size fuel tank do you have on yours? Single tank or more? thanks
L H G	posted 04-22-2009 11:25 PM ET (US) [Changed TOPIC to the fuel economy of another motor. Please begin a new discussion to change the topic to the fuel economy of another motor.]
Tohsgib	posted 04-23-2009 11:09 AM ET (US) I had a Pate 27 but when I repowered it with a Suzuki 70 4stroke the gas would bad so I got rid of it(actually still in my shed). Depends on how far you go but a single 6 is not gonna cut it at 4.5GPH at cruise. I would go with a Moeller 26 under the RPS.