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- Thread starter FIMAN1
- Start date
In a well balanced 22, especially with trim tabs and/or Permatrim, the bow doesn't rise much at all through the range of speeds. However 7-8 knots isn't a very efficient speed for this size boat, you are pushing a lot of water. I much prefer an easy 5-6 knots at 1800-2000 rpm.
-Mike
-Mike
FIMAN1":2vdxydne said:How does the C Dory 22 handle at trawler speed 7-8 knots. will the bow stay down and plow like a trawler? or will it want to rise. My only experiences have been center consoles that need to get on plane or the bow is up.
Thanks in advance for your help
IME, hull speed for a 22 is ~4.5 mph. The boat will be flat.
Tabs and permatrim don't do much if the boat is not planing.
EQ harbor installed a Tohatsu 9.9 FI to sit next to the Honda 90 on our C-dory 22, "Notayot"
I am curious as to fuel efficiency of using this small efi motor at the optimum hull speed for fuel efficiency.
Thoughts on this vs running the 90 hp honda?
We have had the boat since October, hope to take it out for the first time on Lake Whatcom in the next week or so to get a feel for it .
johnd Acme wa
I am curious as to fuel efficiency of using this small efi motor at the optimum hull speed for fuel efficiency.
Thoughts on this vs running the 90 hp honda?
We have had the boat since October, hope to take it out for the first time on Lake Whatcom in the next week or so to get a feel for it .
johnd Acme wa
The running waterline length of the C Dory 22 is 19 feet. The traditional formula is square root of LWL, x 1.34, is max displacement speed in knots: Thus the max displacement speed (before the boat begins to climb over the bow wave, is 5.8 knots. [6.67 statute miles per hour]. If you go with the more efficient square root of the length water line: it is 4.36 knots [5.02 statute miles per hour].
There are several "performance tests"on the C Dory 22. Boat Test.com is now charging for their performance numbers, but Honda did a test in 1999, with a very light boat, and a 70 hp 4 stroke.
1500 RPM. 4.0 mph. 13.8 miles per gallon
2000 RPM. 6.0 mph. 7.5 miles per gallon
2500 RPM. 6.8 mph. 6.8 miles per gallon
3000 RPM. 7.9 mph. 5.6 miles per gallon
You have to jump up to 5000 RPM to get the same mileage you get at 3000 RPM
5000 RPM. 16.1 mph. 5.6 miles per gallon
These numbers are a bit off from what most of us experience, because they were using the 70, with an 11.5" x 13" prop. With a 90 and 15" pitch prop, the speeds would be higher. However the general trend remains the same.
The boat is extremely efficient at low speeds--ie 4 mph or even 6 mph. By the time you get up to 8 miles per hour, you are less efficient than at planing speeds.
Pushing the bow down at lets say 8 mph will only decrease the speed, and efficiency. The only reason to do this would be a better ride in some really steep chop.
The small motor will probably be slightly more efficient at the lower hull speeds--it only takes about 4.5 hp to get the C Dory 22 to 5 mph. There are some issues with efficiency ref prop size with the smaller motors. Most 9.9 are set up for fast aluminum skiffs--but if you got one with a "big foot" or "sail drive"--that is a larger and lower pitched propeller, it will be considerably more efficient. I don't think anyone has run the numbers on this--but I would suspect perhaps 20% more efficient than the 90 hp.
Generally the kicker motors are best for slow speed trolling and "get home" at hull speed. A 3.5 hp will get the boat home at 4 mph or so in calm water. But it may not push the boat well against heavy seas and winds. My father's wooden sailboat had a hull form very similar to the C Dory 25--and about the same air resistance (tall mast = pilot house). We used a 5 hp Johnson from the mid 1930's and would get a steady 5 mph. When we could no longer get parts, my dad purchased a 9.9 HP, and it also got 5 mph, at a higher RPM...and a little more fuel use. The early 5 hp had a larger diameter and lower pitch prop. This is why I am comfortable with a 3.5 HP as my kicker/dinghy motor. But I realize I cannot beat into heavy wind and seas--but I can have steerage way, and get to some point of safety if necessary.
There are several "performance tests"on the C Dory 22. Boat Test.com is now charging for their performance numbers, but Honda did a test in 1999, with a very light boat, and a 70 hp 4 stroke.
1500 RPM. 4.0 mph. 13.8 miles per gallon
2000 RPM. 6.0 mph. 7.5 miles per gallon
2500 RPM. 6.8 mph. 6.8 miles per gallon
3000 RPM. 7.9 mph. 5.6 miles per gallon
You have to jump up to 5000 RPM to get the same mileage you get at 3000 RPM
5000 RPM. 16.1 mph. 5.6 miles per gallon
These numbers are a bit off from what most of us experience, because they were using the 70, with an 11.5" x 13" prop. With a 90 and 15" pitch prop, the speeds would be higher. However the general trend remains the same.
The boat is extremely efficient at low speeds--ie 4 mph or even 6 mph. By the time you get up to 8 miles per hour, you are less efficient than at planing speeds.
Pushing the bow down at lets say 8 mph will only decrease the speed, and efficiency. The only reason to do this would be a better ride in some really steep chop.
I am curious as to fuel efficiency of using this small efi motor at the optimum hull speed for fuel efficiency.
The small motor will probably be slightly more efficient at the lower hull speeds--it only takes about 4.5 hp to get the C Dory 22 to 5 mph. There are some issues with efficiency ref prop size with the smaller motors. Most 9.9 are set up for fast aluminum skiffs--but if you got one with a "big foot" or "sail drive"--that is a larger and lower pitched propeller, it will be considerably more efficient. I don't think anyone has run the numbers on this--but I would suspect perhaps 20% more efficient than the 90 hp.
Generally the kicker motors are best for slow speed trolling and "get home" at hull speed. A 3.5 hp will get the boat home at 4 mph or so in calm water. But it may not push the boat well against heavy seas and winds. My father's wooden sailboat had a hull form very similar to the C Dory 25--and about the same air resistance (tall mast = pilot house). We used a 5 hp Johnson from the mid 1930's and would get a steady 5 mph. When we could no longer get parts, my dad purchased a 9.9 HP, and it also got 5 mph, at a higher RPM...and a little more fuel use. The early 5 hp had a larger diameter and lower pitch prop. This is why I am comfortable with a 3.5 HP as my kicker/dinghy motor. But I realize I cannot beat into heavy wind and seas--but I can have steerage way, and get to some point of safety if necessary.
FIMAN1":1dhlysgj said:How does the C Dory 22 handle at trawler speed 7-8 knots. will the bow stay down and plow like a trawler? or will it want to rise. My only experiences have been center consoles that need to get on plane or the bow is up.
Thanks in advance for your help
Bob did the math for you. I frequently cruise at "slow cruise" speed. The 4.3 knots is really nice if you like a quiet ride. At that speed there is no bow wave, barely a hull ripple and you have plenty of time to look around and enjoy the scenery. More fuel efficient also.
Harvey
SleepyC :moon