Fuel economic boats?

I've been reading through the threads regarding the use of sail vs engine for long distance journies (from what i can gather it costs about the same to run/maintain the boat) but i've been unable to find an approximate distance per liter obtained by an economic diesel boat. I only ever sail so I have no concept of how far a motor powered (+/- 50 foot) boat can travel on one tank or how big the tanks are. Can any one give me a general idea? thanks for your help in advance.

 

Summer Moon, Geer, is 82 feet, and seems to use about a gallon a mile...
http://www.gerrmarine.com/power_90.html

 

Fuel efficiency

Here's two sets of figures to ponder

11metre, cat, power semi-displacement 18kns 18lts per hr
http://www.nobleengineering.com.au/

mono, sloop, 15t (metric) 55hp yanmar, var. pitch, 14.4m LWL
predicted (@41hp,2000RPM) 8kns - 4lts per hr

There is also another mono quoted on boat design but i am unable to find which is very low fuel consumption from a Sabre

 

Dave Gerr's "The Nature of Boats" has diagrams and information how speed, displacement and hull form affects fuel consumption, also a fun book to read

 

Speed is what costs money.

If you are willing to travel at SQ Rt LWL X .8 only about 1 hp per ton of displacement is required.

With a modern diesel 20 hp can be obtained from a gal of fuel.

This rule goes out the window if the vessel has an L to B ratio of over about 6 -1.

They can go about 2x faster on the same fuel.

FF