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Author Topic:   Fuel Consumption of 115-HP Engine

Cross Tackle posted 08-04-2015 03:31 PM ET (US)
What [will be] a ball park figure for fuel consumption [of a 115-HP two-cycle classic outboard engine]? I have a 1997 Boston Whaler Cross Tackle 17 with a 1997 Johnson 115 Ocean Runner.
jimh posted 08-05-2015 09:12 AM ET (US)
Older two-cycle engine fuel consumption can be roughly estimated in gallons-per-hour by dividing the horsepower by ten. A 115-HP older two-cycle engine will consume about 11-GPH at full throttle.
Fuel consumption at lower throttle settings will be proportionally less.
Don SSDD posted 08-06-2015 05:03 AM ET (US)
Jim, just curious, what's your rule of thumb for a modern [four-strok-power-cycle engine or an Evinrude E-TEC engine] in GPH?
Don
Peter posted 08-06-2015 07:27 AM ET (US)
Divide by 11.
jimh posted 08-06-2015 08:26 AM ET (US)
I don't have a rule of thumb for modern engines because they seem to vary all over the map. A small-displacement engine with very big supercharger boost like a Mercury VERADO may burn more fuel than an old two-cycle engine, while a really modern, direct-injection, computer-aided design, using computational fluid dynamics to analyze the combustion chamber processes, like an Evinrude E-TEC G2, will easily use less than half as much fuel as an old two-cycle.
jimh posted 08-06-2015 08:30 AM ET (US)
The other problem with older two-cycle engines: at idle and low speed operation their fuel consumption is horrible. They'll be burning 2-GPH or more as a minimum. A modern 115-HP outboard engine that uses a stratified charge mode of combustion, like an Evinrude E-TEC, can operate at low speeds with a fuel consumption rate of only 0.15-GPH. That is less than one-tenth of the fuel an older engine will be burning at the same engine speeds.
With older two-cycle engines, the only really decent fuel economy comes at about three-quarter-full throttle. At low speeds they'll drive you crazy with the fuel they'll burn.
leadsled posted 08-06-2015 09:11 AM ET (US)
My 1989 Outrage 18 with a new 115 ETEC has burned 175 gallons of fuel in 100 hours. Not a lot of high speed driving
jimh posted 08-06-2015 03:34 PM ET (US)
LEAD'--thanks for that excellent information. The E-TEC 115-HP has been averaging a fuel consumption of 1.75-GPH. That is very good data.
jimh posted 08-06-2015 03:38 PM ET (US)
For some more data about long-term average fuel consumption of modern engines compared to older engines, see

E-TEC 225: Long Term Data
http://continuouswave.com/ubb/Forum4/HTML/007960.html
Don SSDD posted 08-07-2015 04:35 AM ET (US)
Thanks Jim, I probably read those posts at the time and then forgot them. Good data.
Don
Peter posted 08-07-2015 07:41 AM ET (US)
The long term data reveals that it is a mistake to make a purchase decision for an outboard motor based on its WOT fuel consumption. In fact, the cost difference resulting from the average fuel consumption or economy over time between any two motors is usually insignificant.
According to data posted on ContinuousWave, the ICOMIA duty cycle hourly fuel burn rate for the E-TEC 115 is 2.3 GPH. Let's assume that hourly fuel burn for the Johnson 115 Ocean Runner is 35 percent higher for the same duty cycle. That means it would burn about 3.2 GPH, a 0.9 GPH difference for each operating hour. If you ran the motor for 5 hours in a day, the operating cost difference is less than $15. That's between old and modern technology motors. The difference between new technology motors is likely to be on the order of 0.1 GPH over the average - about $1.50 in fuel cost difference for a 5 hour operating day. Over the typical 50 hour season, the fuel cost difference for one modern technology 115 HP outboard versus another is under 20 bucks and between older and modern technology under 200 bucks.
That's why I get a chuckle out of all the fuel consumption/economy discussion when deciding which modern motor to buy. It doesn't make any significant difference in the grand scheme of boating costs.
jimh posted 08-07-2015 10:24 AM ET (US)
Peter makes a good point. An additional element in the consideration of fuel cost savings is, of course, the price of gasoline fuel. Several years ago gasoline was selling above $4-per-gallon on the highway in the USA, and at remote marinas in Canada where I was boating, gasoline was selling above $6-per-gallon. At that time I had an old two-cycle engine. We were trying to make our way upwind into some tall seas, and the boat was getting about 1.2 MPG. I was thinking to myself, "It is costing me five-dollars-per-mile in fuel to move this boat; I can't afford to go boating at that price."
Recently I purchased gasoline on the highway in the USA for $1.55-gallon. That low price was due to use of a discount incentive based on my monthly shopping at the grocery store (KROGER) that is also the fuel retailer. With a trailerable boat, like a 17-footer that we are discussing here, it is not difficult to buy fuel for the boat on the highway. When you can buy gasoline fuel at prices below $2-per-gallon, the fuel consumption of a 1997 Johnson 115-HP Ocean Runner does not represent much of a burden to boat ownership or boat operation.
Peter posted 08-07-2015 10:46 AM ET (US)
You need to look at the differential cost not the absolute cost. If with the old motor it cost $5 per mile and one assumes a 35 percent increased efficiency on average (not the instant where you are encountering tall seas and strong head winds), then the new motor would cost $3.70 per mile. A difference of a $1.30 per mile. If you ran 1000 miles per year your differential fuel cost would be $1300. If the repower costs $15,000, then the break even period is 11.5 years assuming $6 per gallon gas. As the price of a gallon of gas drops, that break even period grows longer.
Repower to increase fuel efficiency rarely ever makes economic sense.
tedious posted 08-17-2015 04:31 PM ET (US)
Re-powering pretty much never makes economic sense, In my case: take a $5,000 boat, add an $8,000 motor, and end up with a package worth maybe $10,000 on a good day, to the right person. Some would say that owning a boat at all, especially an older one, is nonsensical.
But I will point out that the improved mileage can also lead to a dramatic increase in range over older motors, and that may make a lot of difference in some situations.--Tim

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Author	Topic: Fuel Consumption of 115-HP Engine
Cross Tackle	posted 08-04-2015 03:31 PM ET (US) What [will be] a ball park figure for fuel consumption [of a 115-HP two-cycle classic outboard engine]? I have a 1997 Boston Whaler Cross Tackle 17 with a 1997 Johnson 115 Ocean Runner.
jimh	posted 08-05-2015 09:12 AM ET (US) Older two-cycle engine fuel consumption can be roughly estimated in gallons-per-hour by dividing the horsepower by ten. A 115-HP older two-cycle engine will consume about 11-GPH at full throttle. Fuel consumption at lower throttle settings will be proportionally less.
Don SSDD	posted 08-06-2015 05:03 AM ET (US) Jim, just curious, what's your rule of thumb for a modern [four-strok-power-cycle engine or an Evinrude E-TEC engine] in GPH? Don
Peter	posted 08-06-2015 07:27 AM ET (US) Divide by 11.
jimh	posted 08-06-2015 08:26 AM ET (US) I don't have a rule of thumb for modern engines because they seem to vary all over the map. A small-displacement engine with very big supercharger boost like a Mercury VERADO may burn more fuel than an old two-cycle engine, while a really modern, direct-injection, computer-aided design, using computational fluid dynamics to analyze the combustion chamber processes, like an Evinrude E-TEC G2, will easily use less than half as much fuel as an old two-cycle.
jimh	posted 08-06-2015 08:30 AM ET (US) The other problem with older two-cycle engines: at idle and low speed operation their fuel consumption is horrible. They'll be burning 2-GPH or more as a minimum. A modern 115-HP outboard engine that uses a stratified charge mode of combustion, like an Evinrude E-TEC, can operate at low speeds with a fuel consumption rate of only 0.15-GPH. That is less than one-tenth of the fuel an older engine will be burning at the same engine speeds. With older two-cycle engines, the only really decent fuel economy comes at about three-quarter-full throttle. At low speeds they'll drive you crazy with the fuel they'll burn.
leadsled	posted 08-06-2015 09:11 AM ET (US) My 1989 Outrage 18 with a new 115 ETEC has burned 175 gallons of fuel in 100 hours. Not a lot of high speed driving
jimh	posted 08-06-2015 03:34 PM ET (US) LEAD'--thanks for that excellent information. The E-TEC 115-HP has been averaging a fuel consumption of 1.75-GPH. That is very good data.
jimh	posted 08-06-2015 03:38 PM ET (US) For some more data about long-term average fuel consumption of modern engines compared to older engines, see E-TEC 225: Long Term Data http://continuouswave.com/ubb/Forum4/HTML/007960.html
Don SSDD	posted 08-07-2015 04:35 AM ET (US) Thanks Jim, I probably read those posts at the time and then forgot them. Good data. Don
Peter	posted 08-07-2015 07:41 AM ET (US) The long term data reveals that it is a mistake to make a purchase decision for an outboard motor based on its WOT fuel consumption. In fact, the cost difference resulting from the average fuel consumption or economy over time between any two motors is usually insignificant. According to data posted on ContinuousWave, the ICOMIA duty cycle hourly fuel burn rate for the E-TEC 115 is 2.3 GPH. Let's assume that hourly fuel burn for the Johnson 115 Ocean Runner is 35 percent higher for the same duty cycle. That means it would burn about 3.2 GPH, a 0.9 GPH difference for each operating hour. If you ran the motor for 5 hours in a day, the operating cost difference is less than $15. That's between old and modern technology motors. The difference between new technology motors is likely to be on the order of 0.1 GPH over the average - about $1.50 in fuel cost difference for a 5 hour operating day. Over the typical 50 hour season, the fuel cost difference for one modern technology 115 HP outboard versus another is under 20 bucks and between older and modern technology under 200 bucks. That's why I get a chuckle out of all the fuel consumption/economy discussion when deciding which modern motor to buy. It doesn't make any significant difference in the grand scheme of boating costs.
jimh	posted 08-07-2015 10:24 AM ET (US) Peter makes a good point. An additional element in the consideration of fuel cost savings is, of course, the price of gasoline fuel. Several years ago gasoline was selling above $4-per-gallon on the highway in the USA, and at remote marinas in Canada where I was boating, gasoline was selling above $6-per-gallon. At that time I had an old two-cycle engine. We were trying to make our way upwind into some tall seas, and the boat was getting about 1.2 MPG. I was thinking to myself, "It is costing me five-dollars-per-mile in fuel to move this boat; I can't afford to go boating at that price." Recently I purchased gasoline on the highway in the USA for $1.55-gallon. That low price was due to use of a discount incentive based on my monthly shopping at the grocery store (KROGER) that is also the fuel retailer. With a trailerable boat, like a 17-footer that we are discussing here, it is not difficult to buy fuel for the boat on the highway. When you can buy gasoline fuel at prices below $2-per-gallon, the fuel consumption of a 1997 Johnson 115-HP Ocean Runner does not represent much of a burden to boat ownership or boat operation.
Peter	posted 08-07-2015 10:46 AM ET (US) You need to look at the differential cost not the absolute cost. If with the old motor it cost $5 per mile and one assumes a 35 percent increased efficiency on average (not the instant where you are encountering tall seas and strong head winds), then the new motor would cost $3.70 per mile. A difference of a $1.30 per mile. If you ran 1000 miles per year your differential fuel cost would be $1300. If the repower costs $15,000, then the break even period is 11.5 years assuming $6 per gallon gas. As the price of a gallon of gas drops, that break even period grows longer. Repower to increase fuel efficiency rarely ever makes economic sense.
tedious	posted 08-17-2015 04:31 PM ET (US) Re-powering pretty much never makes economic sense, In my case: take a $5,000 boat, add an $8,000 motor, and end up with a package worth maybe $10,000 on a good day, to the right person. Some would say that owning a boat at all, especially an older one, is nonsensical. But I will point out that the improved mileage can also lead to a dramatic increase in range over older motors, and that may make a lot of difference in some situations.--Tim