Theory on fuel consumption

[Goldstar225]

Go to boattest.com and look at their reviews. The give both GPH and MPG figures on a huge variety of boats, including bass boats. In general the best MPG for our boats are at idle speed then again in the midrange (3000-4000 RPM).

[Schultz]

I know my old Johnson 150 burned a lot less gas running at 35 mph vs 45 mph (WOT)

[dentpusher]

The direct answer to your question is "NO" . You do not burn more gas if the throttle is the same but RPM's go up due to raising trim and decreasing drag. You actually keep your gph consumption the exact same but increase mpg.

I run digital GPH as I run down the lake,

By the bold printed, quoted text, it sounds like you have a fuel injected motor. That would be a completely different scenario, I believe. With FI, YOU are determining how much fuel is being injected vs what "berudd" and I thought. That being, that a carburetor adjusts the amount of AIR vs fuel allowed in the engine. With a carb, the more air you pump through by allowing the engine to rev more via less prop resistance when you trim out, you are putting more fuel in also.

So what I have been doing, which seems to be the consensus, is that it is best to get on plane to about 3800-4k rpm (which is about where I usually cruise), trim until I start to lose speed (allowing engine to speed up), then once optimum trim/lift is achieved, throttle back to 3800ish rpm for "best" fuel economy, speed and lift.

Other, smarter people please feel to chime in. Sorry I lost track of this question. Been busy working, trying to beat the taxman....

[PolarKraft195]

Put gas in boat, go fishing!

[rjd]

Best answer yet..........

[lpugh]

No one here seems to quite get this:
Pick any rpm range you choose and while maintaining that rpm adjust the trim for the the highest gps MPH you can get. For mercury's this would be 45 to 4800 for the best economy

Vacuum in the intake at higher rpm does not cause the fuel flow, if this was case there would be no fuel flow at wide open simply because there is no vacuum at WOT
It helps to understand this better by thinking in terms of absolute pressure