Engine gas consumption

[efcon]

I recently owned my fathers boat and i have a question. Is there a way to calculate the gas i need when i wanna go fishing or a small trip? Im new to all this and im looking for how much litre per hour for example the boat engine is consuming.

The boat is a 13.8 feet (4.2 meters) inflatable boat with a Johnson 40 (2000 model, BJ40PLSSM) and im running it in seawater.

Thanks in advance.

[Nos4r2]

Approx 4 litres per hour per 10hp at full throttle.

Work to that and give yourself an extra 1/3 of fuel too as leeway.

[Polwart]

As a rough guide - each 10 HP of engine will use 3.8L (1 US Gal) per hour at WOT (wide open throttle). So your 40 HP will use about 15 L per hour at full speed. You'll use less at "cruising speed" but how much less is probably best if you measure it yourself.

Most people try to allow 1/3rd of their fuel for the trip out, 1/3rd of their fuel for the trip back and the last 1/3rd as a reserve/emergencies.

[edit Nos' types faster than me!]

[efcon]

Thanks for your replies, ill try it out