Apologies for the hijack, but this is interesting to me.
Hey boat guy if you don't mind. What is your boat model and length? Do you know it's actual weight? What driveline does it have? Engine, drive ratio, prop pitch? And how is it typically loaded.
My brother just bought a 99 Searay 210 with a 5.0 EFI. It rides great and has lots of room inside.
I'm pretty sure his EFI is giving him better fuel economy than my much lighter boat which has a carburetor and a bigger engine displacement.
Part of my fuel use is the way I enjoy the boat. I don't go wide open often, but I sure like being shoved back in my seat on acceleration!
I often will put in 11 gallons when I carry in my jerry jugs. My seat of the pants observation is that I can get 3 hours from them.
To share: my boat is a 1989 Baja Sunsport 196 with a 1988 Mercruiser 5.7, Rochester Quadrajet carburetor that was rebuilt winter of 2012-13, running 23" and 21" pitch propellers, weight 2300, deadrise 21 degrees. Typical load 2 adults and 83 lb dog, 100 to 200 lbs of fuel and other stuff. So almost 3000 lbs running.
I just got a little hour meter so I guess now's the time to start logging fuel since I can count engine hours.
Gallons per hour improves, that is decreases, for the time the boat idles and runs at headway speeds. Apparently you and I both do some of that!
