Originally Posted by Trapper6L
Back when I used to race Evinrude engines, in stock form we always used the rule of thumb gas mileage at 10% of the max rated horse power per hour. So if that's a 200, it will use 20 gallons per hour at full throttle at max rated rpms. It'll be fairly close. Throttle back to about 35-3800 rpms is where you'll find most often the gas mileage sweet spot is on an Evinrude 2 cycle. Just guessing here but probably a 17" pitch prop.
It's a 175 Larry, good guess. And great info, as usual. The rule I've been taught to follow is the rule of thirds....one third out, one third back and a third to spare, just in case.
We took an 18 footer with 90 Merc offshore 30 miles in the 90's. Boat had an 18 gal tank. We took along 2, 5-gal tanks. Ended up using 12 gal and we were 30 mi out and back plus all day trolling. We caught a ton of fish too.