i have a 225 Honda 4 stroke and and at cruise (4000RPM) which is 40km give or take, and i use around 22ltrs/hr. so i get 1.8km per ltr of fuel. A 12 hr day fishing on the heavy tackle grounds off the gold coast which is 1hr 15 out i use 130Ltrs on average per trip, however the motor doesnt turn off. So a day trolling is around $200.
Cheers
Matty