expected milage per gallon

H

hank heise

New member
Hi

I have a question about miles per gallon on my 2006 C-Dory. I have a 22 foot cruiser, 90 horse Yamaha 4 stroke. I live in North Fort Myers Fl, on the river and can cruise to the gulf of Mexico too. We have tides but not too much, perhaps 1 to 2 feet at most.

I have estimated my milage as 3 to 4 miles to the gallon and I usually run at 4700 or 4800 rpms which results in about 18 to 19 mph based on my GPS.

Question, is there a more econmical running rpm goal without sacrificing speed too much?

Thanks for your input.
 
The only way to improve on that kind of mileage significantly is to drop all the way down to hull speed - 5 or 6 mph. Sounds like you've pretty much found the sweet spot for cruising speed.
 
Hank-

I'd say your right in the middle of the expected mileage curve for a CD-22, based on my mileage ( I have the same boat and same motor), and have read all the discussions on this site since it's inception back in 2003, and several C-Dory sites before that.

" It is what it is", so to speak!

Nice talking with you!

Joe. :teeth :thup
 
In the summer months, I go on an 75-80 mile trip to Little Johnstone Bay from Seward and I consistently burn (tracked over a number of years and countless trips) between 16-17 gallons of fuel at 4400-4600 rpms. In my boat, this rpm puts the boat speed very close to 20mph give or take a bit depending of currents and wind. To save you from breaking out the calculators, at this rate of fuel burn my boat is getting 4.4 mpg with twin honda 45s. Not at all bad considering that these motors are 15 years old with 1200 hours on them.
 
Hi

Thanks for the information so far. Glad to hear that I'm in the middle so to speak. I have played with the motor trim but if it is trimmed down that makes it easier to go through the waves. Trimming up doesn't really add much as near as I can tell. I try to stay away from the trim tabs too since I have heard that only costs you milage. Any other hints would be appreciated as I work to keep it effective.

Yesterday went down to the gulf of Mexico fishing, round trip a little over 50 miles with some slow zones for manatees. It takes about an hour and a half each way, around 22 miles. I put a little over 50 miles total and tried to outrun some rain on the way back and got about 3.75 or 3.9 miles a gallon. I guess I can be happy with the results.

Thanks for the input.
 
I agree that you have about average mileage. But I disagree with you about trim tabs. The trim tabs only increase the mileage, if you "abuse them". The Permatrim, may slightly decrease the mileage, but the trade off for a better ride is in my opinion worth it.

If you trim down--(motor, tabs or Permatrim)--you will put the bow down and get a smoother ride into the chop. But the mileage will suffer. The boat with trim tabs rides much better. You can keep the outboard thrust parallel to the surface of the water, and thus run more effeciently.

What I have done for years, is to set the throttle about where I want it, and then work the trim until I get the most RPM for that throttle setting. That will be the most effecient running angle. (I have flow meters and that makes it very obvious as to what is the most effecient.)

Also remember that the weight of the boat will depend on what mileage you get. A lighter boat will do significantly better. Weight distribution in the boat may also make a difference.

Water conditions will also make a difference, as does wind. A very slight ripple may give slightly better mileage than a dead flat calm water.
 
Glad to hear that I'm in the middle so to speak.
Click to expand...

Well, if TR is at the front of the pack @ 4.4 mpg, and I'm at the back of the pack @ 2.2 mpg, that indeed puts you right in the middle.
I keep thinking that I'll repower when my Johnson 70 dies but it's looking like it may outlast me.
 
With my CD22 and 90 Johnson heavily loaded on my last trip I "eyeball" estimated my overall mileage at almost 3nm per gal. That is almost 3.5 miles per gal. I was not feeling too good about that and thought that something might be wrong. It looks like that it is just what my boat gets.

Steve
 
With my previous 1983 22 ft. Classic I could run 45 miles (from GPS) and put in 9 gals of fuel. 5 mpg. at 4000 rpm and 20 mph. & 90 hp Honda. I trimmed the boat (with the Honda) as neutral as possible and had a cavitation plate DoelFin and no trim tabs.
I believe the old true flat bottom CD's got better mpg than the newer slightly V'ed bottom models but sacrificed the slightly better ride.
 
With my Suzuki 90 and a permatrim I average 3.8 miles per gallon. My boat is loaded for cruising all the time and I've got a fuel flow meter. I do as Bob suggested run the boat up to desired RPM usually around 4800 and trim the motor for best RPM. Watching the fuel flow I've found 4800 to be the best fuel mileage unless I drop off plane at around 6 or 7 MPH at that I think I get around 8 MPG. Actually according to my fuel flow meter there isn't much difference in MPG between 3500 and 5000 RPMs.
 
I have a Honda 90 EFI on my 22' and am only getting 2.0 - 2.2 mpg.
Hell, I was getting 3.5 - 4.0 with the twin 40s.
Something wrong here. I am very dissatisfied with the performance/economy of the new 90.
 
C-Hawk":3kk6xufr said:
I have a Honda 90 EFI on my 22' and am only getting 2.0 - 2.2 mpg.
Hell, I was getting 3.5 - 4.0 with the twin 40s.
Something wrong here. I am very dissatisfied with the performance/economy of the new 90.
Click to expand...

Roger-

Maybe you're propped wrong, or the motor is set quite a bit too deep below the transom, or both, or ???

Joe. :teeth :thup
 
For give my ignorance; just trying to insure I understand this correctly...

Dr. Bob "Thataway" stated the following:

What I have done for years, is to set the throttle about where I want it, and then work the trim until I get the most RPM for that throttle setting. That will be the most effecient running angle. (I have flow meters and that makes it very obvious as to what is the most effecient.)
Click to expand...

I would have assumed a minimum RPM would have been more efficient fuel-wise not a "....most RPM for that throttle setting."

Is this correct, the maximum RPM is more efficient?

Tanks for the clarification.

Take care and be good,
Dan & Tanya Denver
 
The answer to that one is yes. And Bob does exactly what I do. The reason why the rpms get lower on aggressive trim settings (digging the bow into the waves) is because it takes power to lift the back of the boat to put the front of the boat into the waves. And I happen to agree with Bob that when you have trim tabs you are able to run the motors right in the middle which gives your props more bite thus they are running more efficiently than they would be if you had them doing the work as some do with permatrims. How much difference is this? Beats me, but it is some.

As already pointed out, weight makes a difference too. Speed does, as does currents, wind, and a number of others. I run my boat as light as possible and it is not loaded with all those ins and out that some do. I have no generator, no two week supply of food stuff, no canvass top that ultimately provides extra drag and additional weight, no radar arch and radar for additional drag, no big battery banks, and only bring the barest of essential items. Some C-Dory owners bring so much stuff I wonder how they got it all in the boat. It is like wow, you really have a hairdryer, an real fridge, a hot water heater, a blender, microwave, a chain saw, an electric egg poacher, and the list goes on and on. I on the other hand, have some fishing gear and a couple of guns. I guess I am roughing it and don't appreciate the finer things in life......

Hypothetically, if I can get 10 better efficiency with proper trim and another 10 percent by running light, another 5-10 percent for running in the engine's sweet spot, then it doesn't take long for all this to make a pretty substantial difference.
 
C-Hawk":20lmah0r said:
I have a Honda 90 EFI on my 22' and am only getting 2.0 - 2.2 mpg.
Hell, I was getting 3.5 - 4.0 with the twin 40s.
Something wrong here. I am very dissatisfied with the performance/economy of the new 90.
Click to expand...

Wow something must definately be wrong seems like I've read some pretty good fuel burn numbers on the new Hondas. Shorty after getting my boat I added a permatrim and stainless prop and my mileage wasn't good at all. With the motor at what I call neutral trim the permatrim was about 3/4"" below the bottom of the boat. I raised the motor one hole and it made a lot of difference with no cavitation problems.
 
Hi Marvin,

You have essentially the same boat and motor I have. Do you have trim tabs? If you do, do you set the trim tabs before adjusting the motor trim for best RPM?

What size and type prop do you run?

Thanks,
Steve
 
SeaSpray":2299c3ss said:
Hi Marvin,

You have essentially the same boat and motor I have. Do you have trim tabs? If you do, do you set the trim tabs before adjusting the motor trim for best RPM?

What size and type prop do you run?

Thanks,
Steve
Click to expand...

Steve I really only use the trim tabs for side to side trim. I probably could squeak a little better preformance out of it by using them for fore and aft trim but I use the permatrim for that. It's a long story about my prop but it started out life as a 14 X 18 SS Suzuki prop but it was to much pitch. I took it to a prop shop and they measured it and it was actually 14 X 17.25. I had them take two inches out and later added a little cup. I think the Suzuki 14 x 16 SS prop would be a good choice.

One more thing I've read on Hull Truth that other manufactuers off the shelf props don't work as well as the Suzuki props on Suzukis.
 
Thanks Marvin,

I have an aluminium 3x14x19 that was put on by EQ marine when I bought the boat. Never thought of looking at Suzuki props.

Steve
 
thataway":3efnlnbo said:
What I have done for years, is to set the throttle about where I want it, and then work the trim until I get the most RPM for that throttle setting. That will be the most effecient running angle. (I have flow meters and that makes it very obvious as to what is the most effecient.)
Click to expand...

Basically, if you set the throttle at one setting, the metering of the fuel thru the carb or injectors will remain close to the same. The speed of the engine will increase as the boat becomes more effecient to a certain point, and then it begins to decrease. That "Sweet spot" where the boat is using the least fuel for the most RPM is getting the best effeciency of the engine at that speed of the boat. With the Tom Cat I can vary the speed by 10 knots at the same throttle setting with trim. I will be most effecient at the highest speed for the same throttle setting.

In some ways you have to separate speed from RPM--if you start lugging the engine, the RPM will start to go down, as will the fuel mileage!
 
Steve,

Are you sure you are running a 19 pitch prop on the Honda? That is pretty steep. I have gone through 4 different props and have settled on the 14 pitch 3 blade Quicksilver stainless steel. The new Honda is real sensitive to engine loading in getting the best fuel economy. With a 17 pitch I could hardly get 3 mpg. With the 14 pitch prop I can run heavy at 4500 rpm at 15-16 mph and get 3.4-3.5 mpg. As I lighten up the economy improves to around 4 mpg. Pushing it faster than that drops the fuel economy. This is running without the Permatrim. With the Permatrim on, I can run at 12 mph 4100 rpm and 4 mpg heavy but any faster and economy drops quickly.

With the 14 pitch prop I can spin up to 6300 rpm easily without full up motor trim and reach 30.5 mph.
 
Back
Top