low power C-Dory/ Marinaut

[westward]

Some performance feedback: with our 22 Angler (lighter than the cruiser but same basic hull), lightly loaded and on calm water I was able to hit 17MPH with one Honda 40 at WOT and the other out of the water. I had Permatrims. The boat was definitely lugging the engine at that point and it's nothing I would recommend doing on a regular or long-term basis. I do think a single 70 with a low pitch prop would be OK as long as you went slower and kept it in a reasonable rpm range. Hard to imagine being able to re-sell a CD22 with a single 50 very easily. The single 50 would be fine if you were content withdisplacement speeds and an infrequent emergency burst of speed. Overall, I'd advise against it. Mike.

[Wayne McCown]

I'll add my two cents to this discussion. I have a 1999 CD-22 with twin Honda 40's (which I love). Lightly and evenly loaded and with Permatrims, I can get up on plane at 11 mph and hold plane at 9 mph. One engine will do this easily.

However, cruising the Erie Canal (where the speed limit is 10 mph), I find that running both motors makes for a much more pleasant ride: the rpms are much lower than with one motor and it seems quieter.

I have tried to ascertain the difference in gas mileage: it seems imperceptible. Either running one motor or two, I get 6+ mpg at 10 mph.

[marco422]

Lots of information here. My conclusion is that a 40 or 50 will plane the boat fairly easily when properly propped, but with very little reserve power. It seems like a 70 is a sensible minimum. It also seems that the difference in gas mileage will be negligible: that any engine is going to require about the same amount of fuel to deliver the required minimum horsepower. That would be if the required horsepower is delivered within the efficient operating range of the motor (say at 1500-4500 rpm, higher than idle but less than 80%). Plus, the big increase in output from the alternator is a bonus (triple on the Honda). Oh yes-- and resale value is a big issue...

Thanks for all the input!

[thataway]

Over 6 miles a gallon at 10 miles per hour (8.7 knots) is very impressive-- how is that fuel consumption measured? Has anyone else achieved this economy? This means that you are using 1.7 gallons an hour and only using about 24 hp at 2.4 x sq root LWL...

[flrockytop]

[thataway]

For some reason outboard manufacturers don't put out the graphs which show RPM, Torque, Fuel consumption and HP, as do the diesel and gas inboard engine builders.

I have never been successful in finding these, although there are many published for the other engines.

What you can find is the "performance" tests--where the RPM vs fuel burn is given--but usually these are with very light boats, and don't reflect the real world fuel burn.

For example the Suzuki 115 on a sea chaser 18 with total weight somewhere near 1700 lbs.
RPM spreed gal/hr M/gal
3000 8.3 3.40 2.40
4000 26.2 4.80 5.50

Notice how the boat jumps from 8.3 to 26 mph to get on a plane. The C Dories have much less of a transition, and plane at a lower speed.

This is just one example--http://www.suzukimarine.com/boat_builders/boat_tests/

There are a number of other boats with the 115, but nothing tested really like the C Dory. This may well show us why no curves. The boats act so much differently--depending on hull design, weight, props etc....

I have an 18 foot Century with 115 Yahama total weight close to 2000 lbs, and I have to get it up to 3500 RPM to get it on a plane--and it falls off the plane as I drop much below the 3500 level. As it breaks out of the semidisplacement mode, it goes from 9 mph to 15 mph, and will not run inbetween the two speeds.

[flrockytop]