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#1
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Low RPM = More Fuel?
I was told that running a larger motor (15hp at half throttle to get 7kts which is the hull speed for a particular boat), will use more fuel than the intented design motor of 9.9hp at full throttle. I always thought that using less throttle to achieve a certain speed would consume less fuel than a smaller motor at full throttle. Am I off base on this? Someone please set me straight on this.
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#2
10-11-2017, 05:58 PM
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A lot of variables in that equation, but if your talking old school carbed 2 strokes. Rule of thumb, 9.9 will burn 1 gph wot and a 15 will burn 1.5 gph wot. So if the 15 will get the job done at half throttle, should be less fuel per hour.
That's my take, but some one smarter will probably be along later
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#5
10-12-2017, 12:47 AM
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For that size engine, you won't see much difference. It takes X amount of fuel to make Y amount of HP, and Y amount of HP to go Z in speed. It's not like you're comparing a small 2 cylinder kicker to a 4 cylinder primary pusher engine. I doubt you would see a huge difference if both kickers were propped the same. And I would say prop choice plays a bigger role in fuel consumed than the difference between a 9.9 and 15.
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2011 SUNDANCE B20CCR SKIFF, 2011 YAMAHA 90HP 4 STROKE, 2011 KARAVAN SINGLE AXLE ALUMINUM TRAILER, LOWRANCE ELITE-7 HDI, MINN KOTA RIPTIDE TROLLING MOTOR 2000CC HYDRA-SPORT 225+HP EVINRUDE SOLD  AND THE PINK JEEP!!!! R.I.P. http://www.wellcraftv20.com/communit...ad.php?t=11664 
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#6
10-12-2017, 06:28 AM
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Low RPM = More Fuel?
I agree with you on propping correctly. I was not so much concerned about the cost of the fuel consumption as I was about the comment the fellow made to me regarding the two different sized motors on the same boat targeting the same speed. It just simply did not seem correct to my thinking. Just because one would be using a little larger motor and lugging it (according to him), about half throttle to achieve the same speed as the smaller motor means you would burn more fuel. That is the reason I reached out the forum in order to get some solid impute and confirm I have not been asleep for the past 68 years.
Still looking for my V20! Thanks guys.
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