Mate has a 540 freedom sport and never has to use it to empty. Sometimes we come back with 1/4 of a tank left when we refil but the gauge isn't too flash. What engine have you got ? And where abouts are you planning on fishing. We comfortably get to 12 mile and back via long reef in a bit of wind and have 1/4 left most trips if we leave from Davidson park out through the heads, engine is a 100HP Yamaha 4 stroke. That's with 2 people on board. Add more petrol for extra wind, travel time, engine differences and people on board