I have read many times (accounts) of 40ft motor
sailors and trawlers getting very efficient fuel consumption while "sipping fuel" and still cruising at about 6-7 knots. They usually have 100hp+ engines and rather large fixed props and use low cruising RPMs. As I recall
, many quoted about 1 gallon per hour at about 7 knots. Even less fuel burn at slower speeds.
Here is a quote about fuel consumption of a very different boat, Dashew FPB64. Note that this is for a FULLY loaded boat that has enough fuel aboard to go 9,000 miles on power.
"Another part of this equation is payload, both personal, ships gear
, and liquids. Within the definition of full load are the following allowances:
Fuel and water – 11,600 kg/25,600 lbs.
Spares, tools, ground tackle, personal gear – 3600 kg/8000 lbs.
Evaluation of how the design meets its goals has to be done in the context of a fully loaded condition, with the factors of safety
inherent in the scantlings described above
Boat Speed, Fuel Burn, and Range
For recent real world data during four contentious passages, click here.
In smooth water, no wind
, full load configuration the FPB 64 is hitting its numbers as predicted (we’ll just discuss the highlights here):
At 8.6 knots we are burning 11.8L/3.12 gallons an hour which gives smooth water range of over 9000 nautical miles.
At 9.7 knots fuel burn is 18.9L/5.0 gallons per hour with a range of 5700 miles.
Top speed at full load is 11 knots, not bad from a 236 HP engine
So, we’ve got the ability to carry lots of payload, quickly and efficiently, with extra factors of safety
discussed in the preceding section. We think this makes an excellent foundation for the rest of our evaluation.
You may be wondering “why you need all that range?” At 8.6 knots you could cross the Atlantic four times before running out of fuel."
"You will find this new design summarized below, and then detailed explanations of the various features on the sidebar to the left under the heading “FPB 64″. But first, some basic specifications:
LOD 64.95′ / 19.85m
LWL 63.6′ / 19.4m
17.04′ / 5.22m
Extreme Beam (edge of rub rails) 17.72′ / 5.42m
at half load (75,000 lbs/34 tons) Canoe Body 3.25′ / 1m
at half load (75,000 lbs/34 tons) Prop Skeg 4.5′ / 1.37m
Full displacement 90,000 lbs /40,800 kg
Air Draft (top of masts-excluding whips) 25.75′ / 7.85m
Fuel Capacity 3400 US Gallons / 12,800L
Fresh Water Capacity 1800 US Gallons /6800 L
Minimum Range of Positive Stability 130-degrees (half fuel in one tank, full fresh water tanks)
Cruising Speed 9.25-10.0-knots
Top Speed 10.5 knots
Approximate Range 9.0 knots – 6400 NM
9.5 knots – 5500 NM
Note: speeds/ranges are for smooth water, 75,000 pound displacement, clean bottom."
Source of quote: SetSail» Blog Archive » FPB 64 – Theory & Reality