Estimating Range Under Power

The Aegis-Ran sports a Westerbeke 3 cyl. 35 hp.  Model# 35C diesel engine that operates 2500-3000 RPM while cruising. Consulting the literature for this engine:

And, considering the tankage of 75 gal, assuming 2750 RPM (fuel consumption is about 0.8 gal/h), I calculate a range of:

1 h/0.8 gal x 75 gal = 94 h; 94 h x 5 NM/h = 470 NM

However, a friend who has an Alajuela 38 said he had a range of 600 NM while motoring down the West Coast, albeit with a different engine. Assuming, I had 50 gal of storage in Jerry cans, I estimate the range of the boat will be:

1 h/0.8 gal x 125 gal x 5 NM/h = 780 NM (or perhaps closer to 1000 NM)

Once the boat splashes, I will begin keeping an accurate fuel log.

Update: I recently emptied the main fuel tank and measured the volume to be 60 gallons (not 75 as per specs). Together with the 15 gallon day tank that was recently installed, this gives a total capacity of 75 gallons, so the calculation above remains valid. However, I have decided to keep 25 gallons on the deck or in the lazarettes.

1 h/0.8 gal x 100 gal x 5 NM/h = 625 NM (or perhaps closer to 750 NM)

Now that I have fuel level sensors and a fuel monitoring system on the NEMA 2000 network, I will start keeping closer track of actual fuel usage.