1988 Merc 3.0l Fuel consumption

[Nicolasfar]

Hi,
Beginner, first boat, 18.9 Cobia open deck inboard 3.0 L Merc 1988
just rebuilt my carb, mixture screw ajust on the water has manuel shop states
Compression at 125 to 135 on 4 cyl
new spark plug gap at 0.35
timming set at 2 BTC
cap rotor spark plug wires seems new

I was told that those engine had a good fuel economy
Fill half the tank 9 gallon

spend 3 hour , and not alway full open throttle, the water codition were average ok not calm not bad, cost 8 gallon . Even removed the gage in the tank just to make sure i was almost empty
Seem to be high but want to have your opinion and probably advise or possible solutions to improve that.

thank you

 

[achris]

That's about 10 litres per hour... That's very good! I cruise at about 23 knots and use around 28 litres per hour, and that's good.

You don't have a problem to find a solution to.

Boats are not like cars. The engines are under load all the time. They use heaps more fuel than cars.

Chris.....

 

[havoc_squad]

Cars plow through air and the total load weight effect varies on what angle your vehicle is going up or down on the road.

Boats plow through water, which is significantly higher in drag/resistance than air.

The easiest illustration I can say is you can run faster on land than you can run through waist high water. The effects on the engine are just about the same.

 

[Simoniz]

And you dont drive your car with constant wheelspin, whereas the slippage of the prop in the water is considerable.

 

[Scott Danforth]

your boat motor burns 0.4 # of fuel per HP per hr. so depending on load, you can burn a lot of fuel.

your burn rate is really good. if you want fuel economy in a boat, you need to get one with oars or sails.