How many miles can my boat goes ?

[Navy201o]

I bought a 25 ft troophy boat with twin outboard Yamaha 150 hp engines ,the fuel is gasoline and the fuel tank capacity is 400 letres ,I know it is not easy question and it depends on many factors to answer this question , but I need an estimate or rough answer ,how many miles can my boat travel with full tank ( approximately ) with good sea state and weak current ?

[Roy]

I think about 3kms a litre, at average throttle.