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Author Topic:   90 HP Mercury Fuel Consumption

COWBOY posted 05-16-2002 08:20 AM ET (US)
I'm looking for published GPH fuel consumption figures for my new Mercury 90 HP 2 cycle. I know a lot depends on conditions, loading, etc., but would like to see how they compare to what I am getting on my 17 Montauk Flats Boat. Better diesel engine mfgrs.(CAT anyway) publish GPH numbers based on a "typical prop demand curve", and thought maybe same was available for my Merc? Thanks.
whalerron posted 05-23-2002 12:30 PM ET (US)
Somewhere, I recently saw a table with the Merc gph data but I cannot remember where I saw it. Johnson Outboard claimed that the Merc 90 was using 11.1 GPH....
http://www.coopersmarina.com/johnson_90.htm
COWBOY posted 05-23-2002 10:16 PM ET (US)
Thanks, I will take a look. The 11 GPH figure sounds reasonable at WOT and at rated 90 HP. I cruise at 3500-4200 range and would think Mercury would have these numbers but can't seem to find them.
half shell posted 05-24-2002 06:22 AM ET (US)
I know Grady dealers have gph mph info on their boat and engine combos. I am sure Whaler must have that info since Whaler and Merc have the same boss.
foxprops posted 12-31-2005 05:05 PM ET (US)
I have the same setup 17 Montauk / 90 hp 2 stroke and just installed 28 gallon tank. I have not found info so please post it if you do. Thanks
The Chesapeake Explorer posted 01-01-2006 10:28 PM ET (US)
I have a 2004 Yamaha 90 on my 1987 Montauk. Put it on this year. I have been gettin about 4.5 mpg crusing. Your Merc is a bit bigger in size then the Yamaha but results should be similiar. I bought a 3 gallon tank that I carry in the back of my pick up when the gas prices were going out of sight in Sept-Oct 05. I would fill it up and use that for short after work trips because it was a "10 dollar ride" then. I rode from my marina 1 mile south of the Woodrow Wilson I95 bridge to Key Bridge in Wash Dc then back to the control tower at Reagan National Airport on 3 gal gas. Thats about 14 miles. I have twin 12 gal tanks and keep them with about 6 gal in one and 3 gal in the other during this winter season. In summer they will all be full. Ther are two 1 mile no wake zones on this ride so theres running 20 knots and slow going too.

jimh posted 01-01-2006 10:59 PM ET (US)
The answer to this four-year-old inquiry (begun in 2002) is that a conventional two-stroke will burn about about one-tenth of its rated horsepower in gallons-per-hour at full throttle, or a 90-HP will burn about 9-gallons-per-hour, and so on.
You can find more information on how to estimate fuel consumption by using the brake specific fuel consumption method. For outboard motors you can assume the brake specific fuel consumption will be in the range of 0.55 to 0.6 pounds of fuel per horsepower per hour.
http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption will explain more.
WT posted 01-01-2006 11:22 PM ET (US)
COWBOY:
Here's some data so that you can compare your 2 stroke fuel consumption to that of a 90 HP 4 stroke.
http://myweb.cableone.net/barney9014/images/performance.jpg

WT
tombro posted 01-02-2006 06:50 AM ET (US)
Building on Jim's reply of a 2 stroke burning 10% of it's hp in gph: Dropping your throttle from WOT to 3/4 throttle cruise will halve your burn. Which means <5 gph for a 90 horse.
Teak Oil posted 01-02-2006 11:17 AM ET (US)
Pretty much all carb'd two strokes get between 4 and 5 mpg on a 17' hull.
Even in solid 4' waves and working the throttle pretty good I averaged well over 4mpg on a 50 mile trip with my 20 year old OMC 90.

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Author	Topic: 90 HP Mercury Fuel Consumption
COWBOY	posted 05-16-2002 08:20 AM ET (US) I'm looking for published GPH fuel consumption figures for my new Mercury 90 HP 2 cycle. I know a lot depends on conditions, loading, etc., but would like to see how they compare to what I am getting on my 17 Montauk Flats Boat. Better diesel engine mfgrs.(CAT anyway) publish GPH numbers based on a "typical prop demand curve", and thought maybe same was available for my Merc? Thanks.
whalerron	posted 05-23-2002 12:30 PM ET (US) Somewhere, I recently saw a table with the Merc gph data but I cannot remember where I saw it. Johnson Outboard claimed that the Merc 90 was using 11.1 GPH.... http://www.coopersmarina.com/johnson_90.htm
COWBOY	posted 05-23-2002 10:16 PM ET (US) Thanks, I will take a look. The 11 GPH figure sounds reasonable at WOT and at rated 90 HP. I cruise at 3500-4200 range and would think Mercury would have these numbers but can't seem to find them.
half shell	posted 05-24-2002 06:22 AM ET (US) I know Grady dealers have gph mph info on their boat and engine combos. I am sure Whaler must have that info since Whaler and Merc have the same boss.
foxprops	posted 12-31-2005 05:05 PM ET (US) I have the same setup 17 Montauk / 90 hp 2 stroke and just installed 28 gallon tank. I have not found info so please post it if you do. Thanks
The Chesapeake Explorer	posted 01-01-2006 10:28 PM ET (US) I have a 2004 Yamaha 90 on my 1987 Montauk. Put it on this year. I have been gettin about 4.5 mpg crusing. Your Merc is a bit bigger in size then the Yamaha but results should be similiar. I bought a 3 gallon tank that I carry in the back of my pick up when the gas prices were going out of sight in Sept-Oct 05. I would fill it up and use that for short after work trips because it was a "10 dollar ride" then. I rode from my marina 1 mile south of the Woodrow Wilson I95 bridge to Key Bridge in Wash Dc then back to the control tower at Reagan National Airport on 3 gal gas. Thats about 14 miles. I have twin 12 gal tanks and keep them with about 6 gal in one and 3 gal in the other during this winter season. In summer they will all be full. Ther are two 1 mile no wake zones on this ride so theres running 20 knots and slow going too.
jimh	posted 01-01-2006 10:59 PM ET (US) The answer to this four-year-old inquiry (begun in 2002) is that a conventional two-stroke will burn about about one-tenth of its rated horsepower in gallons-per-hour at full throttle, or a 90-HP will burn about 9-gallons-per-hour, and so on. You can find more information on how to estimate fuel consumption by using the brake specific fuel consumption method. For outboard motors you can assume the brake specific fuel consumption will be in the range of 0.55 to 0.6 pounds of fuel per horsepower per hour. http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption will explain more.
WT	posted 01-01-2006 11:22 PM ET (US) COWBOY: Here's some data so that you can compare your 2 stroke fuel consumption to that of a 90 HP 4 stroke. http://myweb.cableone.net/barney9014/images/performance.jpg WT
tombro	posted 01-02-2006 06:50 AM ET (US) Building on Jim's reply of a 2 stroke burning 10% of it's hp in gph: Dropping your throttle from WOT to 3/4 throttle cruise will halve your burn. Which means <5 gph for a 90 horse.
Teak Oil	posted 01-02-2006 11:17 AM ET (US) Pretty much all carb'd two strokes get between 4 and 5 mpg on a 17' hull. Even in solid 4' waves and working the throttle pretty good I averaged well over 4mpg on a 50 mile trip with my 20 year old OMC 90.