A lot of it depends on the boat; a new clean fiberglass bass boat with a smooth bottom will take less fuel than a 50-year-old aluminum pontoon boat with rows of rivets running down the middle of the pontoons.
I rented a John boat with a 15hp Yamaha several years ago. The fuel consumption rate was about one gallon per hour at wide open throttle.
Carborated
100:1
Most all models of Yamaha outboards can be operated on a 50:1 fuel to oil ratio.
The fuel to oil ratio for a 2000 model, 15 hp Yamaha outboard would be 50:1. Roughly 1 pint of 2 cycle oil to 6 gallons of fuel.
Premium gasoline
50:1 ratio
The 1992 model, 25 hp Yamaha outboard requires a 50:1 ratio. One pint of 2 cycle oil, to six gallons of fuel.
Yes !
Sure
50/1
50 to 1. Use good Oil