What is your fuel consumption

[Donald Tyson]

I've seen some of your data. Is there a chart somewhere for all C-Dory boats?

[thataway]

I am not aware of any chart. There will be differences depending on engines, The skipper's skill level, weather / sea conditions and the way the boat is loaded. Also variability in various boats: addition of racks. or other accessories, foils, heavy gear (such as a dive compressor), water intrusion, increased air resistance, or water resistance.

Not all boats have fuel flow meters. The most accurate way is to observe fuel used over a two way course, with stable conditions, using a calibrated vessel to feed the fuel. That is rarely done.

There are generalizations which are close, and are fairly repeatable. The "Boat.com" are often very optimistic. (New boat, lightly loaded, clean bottom). Same for "factory" specs.

What boat, and what engine/s are you interested in?

[ssobol]

On my '08 22 cruise with a Honda BF90D. I plan using 3 mpg. Depending on the load and speed, my actual mpg is between 3.3 and 4 at cruising speeds. Planning with 3 mpg builds in a reserve and accounts for things like idling, battery charging, etc.

[Donald Tyson]

I’m thinking a 25 with 150 or 200hp.

[starcrafttom]

27ft cdory long cabin with 225 honda 2.4 mpg from 14 mph to 30 mph.

[Pacificcoast101]

Twin Honda 150s with heavy dive gear and cameras onboard. We get just over 2 mpg.

[KevinDU]

I have a C-Dory 22. When loaded with 80 gallons of gas and supplies for 8 days with one 180 lbs person on board, my TWIN YAMAHA 50hp get 3 Nautical Miles (3.45 Miles) per gallon. That is at 4200 rpm (12-15 knots)

[JamesTXSD]

With our CD-25 with a Honda 135, I would plan for 2.5 nmpg, usually saw closer to 3 nmpg at high cruise (16 to 20 knots) and 5+ nmpg at displacement speed of 5 to 6 knots. Those numbers are when cruising and loaded accordingly. For any local boating, I would generally keep the fuel tank at 1/3 to 1/2 to keep the weight lower and would see slightly better mileage.

[colbysmith]

On my relatively heavily loaded 25 with a Yamaha 150 4 stroke, I tend to get 4.5mpg at 6mph, and 1.9-2.1mpg on plane. All depends upon current however. Currently on the Tennessee River with currents of 2-3 mph, going against the current I managed an average of 3.5mpg at 1400-1500 RPM or about 5mph. If I remember, on my 22 with a Merc 115hp 4 stroke, hull speed got me close to 6mpg, and on plane was closer to 3 mpg.

[Donald Tyson]

Colby and James. I had no idea there was such a difference in the planing vs the off plane efficiency. Amazing...I had this Idea that it would be the opposite. Thanks for sharing.

[tsturm]

[thataway]

Below are the fuel consumption curves for my last C Dory 25, with a 150 HP Honda, fuel injected. The course was run both ways in a 5 mile stretch of smooth water, with a little current.





As you can see the lower planing speeds, and transition from displacement to planing speed gave the worse fuel consumption figures. At the higher and good planing speeds the mileage smoothed out a just a little under 3mpg. As a boat transitions from displacement speed, and climbs over its bow wave, the fuel consumption is the poorest--yet many motor boat owners run their craft with "Maximum wake" speed--in the 10 to 14 knot range. They are getting the poorest fuel milage.

At the slowest speeds the fuel flow meters are not accurate and often one is getting better than what is registered on the fuel meter.

Tom Cat 255 with two Suzuki 150's I did a run of 200 miles on flat water, minimal current or breeze. The Speed was at 30 knots, except about 4 miles total of "no Wake Zone"--where my speed was 5 knots. Fuel usage was calculated by fill up to fill up and Lowrance fuel flow meters, which I had calibrated. The average for the trip was slightly over 2 miles per gallon. Overall during my ownership and several thousand miles of travel, I figured 1.8 miles per gallon to be on the "safe side".

As I have brought out before that slow speeds use very little HP--and that was illustrated by a 4.5 HP dinghy outboard got my 65,000, LWL 53' LOA 62' Ketch moving at about 2.5 miles per hour--and steerage way, when I lost the transmission on the 90 hp diesel engine. This gave me time to get the 13' inflatable boat with a 25 hp outboard engine pumped up and hoisted onto the water. The 25 hp (not ideal prop size of about 15", vs the diesel prop of 26".) gave us a speed of a little over 5 mph and control to dock the boat a few miles up the harbor. The Max speed was 9 knots and the 90 HP diesel engine running at WOT RPM of 2000. We normally cruised at 6 knots and about a gallon an hour--or 6 N. miles per gallon. The boat had a theoretical Hull speed of 9.8 knots and some were fitted with 120 hp engines, instead of the 90 hp. The larger engine boats would almost reach 10 ,knots. But they were digging a huge hole in the water. The boats full displacement lines, long deep keel, and doubled ended (at the water line) lines meant there was just no lift. On the other hand, I was watch captain on one of my friend's racing 55' Ultralight displacement sloop of only 20,000 lbs Boat, with a daggerboard, and mizzen board, working down wind sail area of about the same as my ketch--close to 3000 sq feet, including spinnaker and main. That boat would plane up to 22 knots in good downwind conditions. On a beam reach speeds over 12 knots were not uncommon with the right sea and wind state--again well beyond the "theoretical hull speed".a

[Donald Tyson]

That is pretty impressive.

[Donald Tyson]

I see the efficiency rebounding on the chart where the engine rpm raises up into some of the higher planing speeds. Would this be even more dramatic with a 200 or 225 on the 25?


I had an Old Pearson Triton (Hull #20 out of Bristol, RI) After rebuilding the entire boat I never re-installed the little Atomic 4. Instead I pushed it everywhere with a 6hp Johnson that I had and loved. I forget what hull speed was...around 6 would be my guess. But that little 6hp had now trouble putting the boat as fast of faster than it could sail. I wonder what MPG it was getting. Fuel seemed to last forever. and it makes me wonder if the auxiliary shouldn't be used more often in C-Dory's if 5knots is all they desire to go.

[thataway]

6 hp would use about 1/2 gallon of gasoline an hour when using the full 6 hp, so you would be getting 12 miles per gallon minimum. This was about the same as my father's 26' fin keel, hard chine sailboat--whose lines were remarkedly like the C Dory 25--freeboard about the same, but cabin house was only about a foot high, so sitting head room only. He had a 1932 Johnson 5 hp--and then went to a 9.9 hp Evinrude, but the old Johnson did as well or better--about 5 mph was the speed we counted on. Yes those sailboats would sail faster than under power.

The Atomic four was "30 hp"--sort of... It only had two main bearings and if pushed too hard, the crank shaft would fail. I had leased my Columbia 29 to a group of 3 who had crewed for my dad when I was in the Army. After about a year they managed to break the crank shaft trying to find out how fast the boat would go under power. The Columbia 29 was very similar to the Triton in its hull shape, length and sail area, the Triton was slightly lighter and wider. The Triton PHRF was 246 and Columbia 29, 228, Which would indicate that the Columbia was about 20 seconds a mile faster.