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Author Topic:   Fuel Economy: Some Observations

jimh posted 07-13-2005 09:43 AM ET (US)
Now that I have a NAVMAN 3100 fuel flow instrument, I have a more accurate record of my fuel consumption. Here are some data from a recent trip:
Boat: REVENGE 22 W-T WD
Motor: Evinrude V6 225-HP two-stroke
Total Distance: 283.8 miles
Total Fuel: 151.3 gallons
Average MPG: 1.875
This is fairly close to my previous seat of the pants estimate of about 1.75-MPG based on coarse measurements of distance and fuel.
The 225-HP two-stroke is a 3.0-liter loop charged engine with carburetors. It has never been known as a fuel miser. The boat was loaded with gear, crew, and fuel, so it probably weighed 4400 pounds or more during most of this cruise.
On one long leg in nice seas we averaged about 1.9 MPG. Coming back over some of that water in rough, upwind conditions the mileage dropped to about 1.6 MPG.
According to the Navman, fuel economy at idle is not very good, about 1.4 to 1.6 MPG.
My impression of newer engines is they have much better fuel economy at idle speeds, often four times better. At cruising speeds the new engines probably only have a 50-percent improvement potential. Although you may spend considerable time at idle, most of the fuel gets burned at cruising speeds.
I would estimate (or guess, really) that if I had a newer engine I would probably get about 3-MPG tops at cruise, which is a 50-percent improvement over the current best cruise economy of about 2-MPG. I would get more like 6-MPG at idle and slow speeds. This could improve my fuel consumption to around, say, an average of 2.875 MPG, or about 1-MPG better than current.
Using this figure, I could have made the trip in 283/2.875=98.4 gallons, or a savings of 151.3 - 98.4 = 52.8 gallons.
Fuel prices were in region of $2.75/gallon on average, so I would have saved about $2.75 X 52.8 = $145 on fuel during the cruise.
Typically we only use the boat like this about 3-4 times a year. My potential from fuel savings would be roughly $145 X 4 = $580 per year.
A new engine would probably cost about $10,000 allowing for some trade-in value on the current engine. To recover the cost of the new engine via fuel savings, at the current rate of use and current fuel prices, would take about 10,000/580=17 years.
The current engine has some virtues: it is quite simple in its design and has relatively low maintenance. It is also paid for and has already undergone most of its depreciation in value. Once you get over the shock of some of those fuel mileage numbers, it still looks like an old friend that you might want to keep around for a while.
Peter posted 07-13-2005 09:59 AM ET (US)
Clearly the economics provide no reason to abandon the old Evinrude. However, it does appear to me that your fuel economy is a bit on the low side from what I would expect based on my years with a notched transom 22 Revenge and a 225.
The only significant advantage of a more fuel efficient motor for you would be that it could extend your cruising range by 30 to 40 percent and that, of course, would only matter if you went on long trips where dockside fuel wasn't readily available.
Outrage22Cuddy posted 07-13-2005 07:43 PM ET (US)
My boat has WD and twin 1991 Yamaha 130's and gets almost identical mileage at cruise speed. Idling with 1 motor raised is better. I also know the frustration of trying to justify the cost of a repower to a more effecient engine. I've vowed not to ever fix my motors when they break in a major way and then will get a 4-stroke single. I've read on another board how someone with a non-WD version of the same boat as mine put on a 150 and that it runs great. I would have to imagine the mpg with a single 4 cylinder 4 stroke would be pretty good. I don't really need all the speed of the twin 2 strokes. I'm tired of the pounding ride at those speeds. Oh, and I run the cheapest 2 stroke oil I can find and no problems yet.
jimp posted 07-13-2005 08:00 PM ET (US)
JimH -
Looks about right. I figured that my old 1989 225 Johnson on my 1990 Revenge 22 WT got about 2 nmpg at 24-25 kts. When the old 225 blew, I replaced it with a 2003 Merc Optimax 225.
On a recent trip to Glacier Bay National Park and the Village of Hoonah, we went 138 nautical miles on 46 gallons of gas = 3.0 nmpg at 29 knots and 3900 RPM (good sized load with extra fuel, water, and camping gear).
Lightly loaded, the 225 Optimax gets about 3.2 nmpg at 3740 RPM and 29.2 knots.
GPS and SmartCraft gauges provide data.
JimP

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Author	Topic: Fuel Economy: Some Observations
jimh	posted 07-13-2005 09:43 AM ET (US) Now that I have a NAVMAN 3100 fuel flow instrument, I have a more accurate record of my fuel consumption. Here are some data from a recent trip: Boat: REVENGE 22 W-T WD Motor: Evinrude V6 225-HP two-stroke Total Distance: 283.8 miles Total Fuel: 151.3 gallons Average MPG: 1.875 This is fairly close to my previous seat of the pants estimate of about 1.75-MPG based on coarse measurements of distance and fuel. The 225-HP two-stroke is a 3.0-liter loop charged engine with carburetors. It has never been known as a fuel miser. The boat was loaded with gear, crew, and fuel, so it probably weighed 4400 pounds or more during most of this cruise. On one long leg in nice seas we averaged about 1.9 MPG. Coming back over some of that water in rough, upwind conditions the mileage dropped to about 1.6 MPG. According to the Navman, fuel economy at idle is not very good, about 1.4 to 1.6 MPG. My impression of newer engines is they have much better fuel economy at idle speeds, often four times better. At cruising speeds the new engines probably only have a 50-percent improvement potential. Although you may spend considerable time at idle, most of the fuel gets burned at cruising speeds. I would estimate (or guess, really) that if I had a newer engine I would probably get about 3-MPG tops at cruise, which is a 50-percent improvement over the current best cruise economy of about 2-MPG. I would get more like 6-MPG at idle and slow speeds. This could improve my fuel consumption to around, say, an average of 2.875 MPG, or about 1-MPG better than current. Using this figure, I could have made the trip in 283/2.875=98.4 gallons, or a savings of 151.3 - 98.4 = 52.8 gallons. Fuel prices were in region of $2.75/gallon on average, so I would have saved about $2.75 X 52.8 = $145 on fuel during the cruise. Typically we only use the boat like this about 3-4 times a year. My potential from fuel savings would be roughly $145 X 4 = $580 per year. A new engine would probably cost about $10,000 allowing for some trade-in value on the current engine. To recover the cost of the new engine via fuel savings, at the current rate of use and current fuel prices, would take about 10,000/580=17 years. The current engine has some virtues: it is quite simple in its design and has relatively low maintenance. It is also paid for and has already undergone most of its depreciation in value. Once you get over the shock of some of those fuel mileage numbers, it still looks like an old friend that you might want to keep around for a while.
Peter	posted 07-13-2005 09:59 AM ET (US) Clearly the economics provide no reason to abandon the old Evinrude. However, it does appear to me that your fuel economy is a bit on the low side from what I would expect based on my years with a notched transom 22 Revenge and a 225. The only significant advantage of a more fuel efficient motor for you would be that it could extend your cruising range by 30 to 40 percent and that, of course, would only matter if you went on long trips where dockside fuel wasn't readily available.
Outrage22Cuddy	posted 07-13-2005 07:43 PM ET (US) My boat has WD and twin 1991 Yamaha 130's and gets almost identical mileage at cruise speed. Idling with 1 motor raised is better. I also know the frustration of trying to justify the cost of a repower to a more effecient engine. I've vowed not to ever fix my motors when they break in a major way and then will get a 4-stroke single. I've read on another board how someone with a non-WD version of the same boat as mine put on a 150 and that it runs great. I would have to imagine the mpg with a single 4 cylinder 4 stroke would be pretty good. I don't really need all the speed of the twin 2 strokes. I'm tired of the pounding ride at those speeds. Oh, and I run the cheapest 2 stroke oil I can find and no problems yet.
jimp	posted 07-13-2005 08:00 PM ET (US) JimH - Looks about right. I figured that my old 1989 225 Johnson on my 1990 Revenge 22 WT got about 2 nmpg at 24-25 kts. When the old 225 blew, I replaced it with a 2003 Merc Optimax 225. On a recent trip to Glacier Bay National Park and the Village of Hoonah, we went 138 nautical miles on 46 gallons of gas = 3.0 nmpg at 29 knots and 3900 RPM (good sized load with extra fuel, water, and camping gear). Lightly loaded, the 225 Optimax gets about 3.2 nmpg at 3740 RPM and 29.2 knots. GPS and SmartCraft gauges provide data. JimP