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Author Topic:   Motor Efficiency and Range

btb posted 09-17-2008 11:47 AM ET (US)
I have a (wonderful) 16SL with the original Yamaha 90 motor. On average I get 3.2 nmpg. If I troll a lot mileage can drop to around 2.5 nmpg. The boat has a 22 gall tank so my maximum range (ignoring the 2/3 rule)is around 70 nm's, with a low of 55 nautical miles.
If I repower with say an e-tec, what effect will it's increased fuel efficiency have on my range? (I say an etec due to weight issues with the 4 strokes - but are there 4 strokes I should consider - what motor weight is too much??). What real-world mpg could I expect from one of these newer motors? Also, I understand they are most efficient at mid throttle settings, - well, I never go at WOT - the ocean is almost never smooth enough for that, so maybe that translates into a few more miles of range?
I thought I needed a bigger boat (with its attendant bigger gas tank) to increase my range - but maybe a newer motor would do the trick.
Bill
Tom W Clark posted 09-17-2008 12:06 PM ET (US)
Bill,
The E-TEC sees the greatest improvement in fuel mileage at idle speeds where conventional two strokes like your Yamaha are very wasteful, so if you do a lot of trolling, you will see a huge increase in range.
WT posted 09-17-2008 12:21 PM ET (US)
If I am doing this correctly, your mileage is 3.2 nmpg or 3.68 mpg on average and 2.5 nmpg or 2.87 mpg.
I'm totally guessing but based on my mileage with a heavier 170 Montauk and 400 pound 90 hp Mercury EFI 4 Stroke (Veradito)outboard. You should probably double your efficiency and range with the E-TEC 90.
Here's an example of one of my long distance runs from Sacramento by river to San Francisco Bay and back.
188.64 miles
7 hours 8 minutes run time
26.46 mph average speed
31.25 gallons of fuel burned.
6.04 miles per gallon
$123.36 cost of fuel
$3.95 cost per gallon of gas. (Marina fuel was $4.20/gallon)
I ran mostly at 4600 rpm or around 29-31 mph.
Warren
Peter posted 09-17-2008 01:06 PM ET (US)
Just to add some numbers to Tom's remarks, a Yamaha 2-stroke 90 at 1000 RPM will consume 1.2 GPH. In contrast, a 90 E-TEC at 1000 RPM will consume about 0.25 GPH, nearly a 1 GPH difference. I think as a general rule, there is at least a 1 GPH difference between these two motors throughout the operating range except, perhaps, at WOT.
As a further comparison, a Yamaha F90 will consume about 0.5 GPH at the same 1000 RPM and won't push a boat as fast as either of the motors due to greater reduction in the gearing.
Tohsgib posted 09-17-2008 01:25 PM ET (US)
Just FYI...I repowered my 17 from a 90 Yamaha to a 70 Suzuki and lost only 2mph at WOT. BUT...I cut my cruising GPH in more than half and at 1000rpm it burns less than a quart an hour. At 30lbs more than an E-yec and since WOT is not that important, give it some thought. My 17 would do about 10mpg at cruise and 25mpg @ 1000rpm.

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Author	Topic: Motor Efficiency and Range
btb	posted 09-17-2008 11:47 AM ET (US) I have a (wonderful) 16SL with the original Yamaha 90 motor. On average I get 3.2 nmpg. If I troll a lot mileage can drop to around 2.5 nmpg. The boat has a 22 gall tank so my maximum range (ignoring the 2/3 rule)is around 70 nm's, with a low of 55 nautical miles. If I repower with say an e-tec, what effect will it's increased fuel efficiency have on my range? (I say an etec due to weight issues with the 4 strokes - but are there 4 strokes I should consider - what motor weight is too much??). What real-world mpg could I expect from one of these newer motors? Also, I understand they are most efficient at mid throttle settings, - well, I never go at WOT - the ocean is almost never smooth enough for that, so maybe that translates into a few more miles of range? I thought I needed a bigger boat (with its attendant bigger gas tank) to increase my range - but maybe a newer motor would do the trick. Bill
Tom W Clark	posted 09-17-2008 12:06 PM ET (US) Bill, The E-TEC sees the greatest improvement in fuel mileage at idle speeds where conventional two strokes like your Yamaha are very wasteful, so if you do a lot of trolling, you will see a huge increase in range.
WT	posted 09-17-2008 12:21 PM ET (US) If I am doing this correctly, your mileage is 3.2 nmpg or 3.68 mpg on average and 2.5 nmpg or 2.87 mpg. I'm totally guessing but based on my mileage with a heavier 170 Montauk and 400 pound 90 hp Mercury EFI 4 Stroke (Veradito)outboard. You should probably double your efficiency and range with the E-TEC 90. Here's an example of one of my long distance runs from Sacramento by river to San Francisco Bay and back. 188.64 miles 7 hours 8 minutes run time 26.46 mph average speed 31.25 gallons of fuel burned. 6.04 miles per gallon $123.36 cost of fuel $3.95 cost per gallon of gas. (Marina fuel was $4.20/gallon) I ran mostly at 4600 rpm or around 29-31 mph. Warren
Peter	posted 09-17-2008 01:06 PM ET (US) Just to add some numbers to Tom's remarks, a Yamaha 2-stroke 90 at 1000 RPM will consume 1.2 GPH. In contrast, a 90 E-TEC at 1000 RPM will consume about 0.25 GPH, nearly a 1 GPH difference. I think as a general rule, there is at least a 1 GPH difference between these two motors throughout the operating range except, perhaps, at WOT. As a further comparison, a Yamaha F90 will consume about 0.5 GPH at the same 1000 RPM and won't push a boat as fast as either of the motors due to greater reduction in the gearing.
Tohsgib	posted 09-17-2008 01:25 PM ET (US) Just FYI...I repowered my 17 from a 90 Yamaha to a 70 Suzuki and lost only 2mph at WOT. BUT...I cut my cruising GPH in more than half and at 1000rpm it burns less than a quart an hour. At 30lbs more than an E-yec and since WOT is not that important, give it some thought. My 17 would do about 10mpg at cruise and 25mpg @ 1000rpm.