Yes, on my F150, over many trips I
got a mile or 2 better with boats on it.
That makes the most sense yet.
I get about 4-6 mpg better on straight highway versus city/highway/traffic mixed. Likely, that was his difference, and the canoe was coincidental, and not enough negative influence to overcome the benefit of highway speed.
YoS
Too many variables
You would need to drive the exact same route without the canoe, in the same type of wind and traffic conditions, to know if the canoe might actually improve the airflow over your car.
I suppose it is possible, but usually when someone rooftops their boat(s) the mileage drops, often quite a lot.
driving wrong vehicles ?
I typically see a 2 mpg reduction w/ my canoe on racks, 3+ mpg loss w/ 2 canoes up
There are very few situations
where increasing your cross section or adding weight to your vehicle can improve your mileage.
If this were a real effect, people would be putting canoes on all their vehicles these days!
Driving a constant speed between 45 and 65 will almost always give you much better mileage than stop and go stuff. Your miles per gallon at the red light is zero (if your engine is running). That is one of the primary benefits of hybrids – they shut down the engine when stopped.
jim
Must have been down hill…
– Last Updated: May-07-08 5:49 AM EST –
both directions, with the wind at your back !
I think I'll try three canoes next time instead of two
cheers,
jackL
Most likely
The most probable is that my fuel mileage increased because I accelerated and slowed down much more smoothly. I guess I need to change my driving style.
that happened to me
when my other car came down with a problem, right before our vacation, we decided to strap the 17’ grumman barge on the top of our volkswagon beetle. our gas milage actually did increase a little. this was back around 1980 so i can’t produce the exact numbers but we were both quite surprised.
Nope, but …
Never got better mpg with canoe on top, but never got worse mpg either. I have a 1999 Subaru Forester with 190,000 miles on it. I always get about 23 mpg no matter what: boats no boats, racks no racks, loaded with boats or just me. The only time I get worse mpg is with two canoes on top and head or side winds. The only time I get better mpg is when I drive slower on the highways.
It must also be HP and gearing
related. The pick-ups I’ve owned pretty much got the same mileage regardless of conditions.A full sized truck is going to feel the impact of a couple of boats a whole lot less than a 4 banger.
Lower MPG w/canoe.
We always get lower mpg with the canoe on top. More wind = even less mpg. If you are getting better mpg it is most likely as said that you are driving your vehicle with a “softer” approach. I never whip around the corners like I usually do with a canoe on the roof. They say it’s a good idea to drive everyday like you had a glass of water sitting on your dash.
Tom
yes
but I have to be paddling really hard.
Aerodynamics contributes about
70% of your cars resistance to movement or total perceived friction. The rest is from engine friction, tranny friction, tire rolling resistance, and wheel bearing friction.
A canoe, on certain vehicles, may actually enhance the aerodynamics due to filling in open areas that usually would create drag. A pickup truck with a level canoe riding close to the roof would be most likely to show a benefit like this.
I am uncertain of your vehicle profile, but despite what we see, the wind often reacts differently than we might predict. The weight of the canoe is less than a person, so no significant effect from the weight given the total weight of you and car and boat. The aerodynamics is the key to mileage.
Most vehicles will have a worse aero effect with the canoe on top, but not all.
AMC Eagle gets better mileage w/
I drive an 85 AMC that gets better mileage with a canoe. I have driven it locally and on the highway with and without the canoe. In both types of driving it gets better mileage with one canoe. Locally with 1 canoe, I get 1-2 mpg better. On the highway, I get 4-6 mpg better than I would on the highway without a canoe.
Generally, when I add a second canoe, the mileage drops 4 mpg.
Racks are culprits
I had a mid-90’s Intrepid, a very aerodynamic design that got good mileage for a full sized, well powered car (in the mid to high twenties). Yakima racks killed the mileage on this car, cut it about 4mpg. Put a canoe on those racks, and the mileage would bump back up to near normal. The canoe didn’t really improve on the Intrepid’s aerodynamics, but it prevented the turbulence caused by the racks, and improved the vehicles the mileage of the vehicle in racked configuration.
Only one boat gave me better mileage
It was a 13.5 Perception America. I always got a mile or two more a gallon when I carried it. No other boat gives me more MPG but it’s still about the same.
physics
Being an automotive engineer type nerd I have to jump in.
Force of drag = 1/2 * rho (air density) * Cd (coeffient of drag…shape factor) * A (frontal area) * v**2 (velocity squared).
Assuming that you are driving at same speed in similar atmospheric conditions then you will get better gas mileage if the canoe improves your shape factor enough to offset the increased frontal area. A canoe could indeed help smooth the airflow over the rear of a vehicle…the aerodynamically messy area. It sure seems plausible to improve gas mileage is some cases (like a pick-up truck) and someone should contact Mythbusters.
Physics / fluid dynamics anyone?
All other variables being equal, it is essentially impossible to get better gas mileage with a canoe on a car vs. without. Might have better luck exceeding the speed of light or time travelling. As above, “other” variables are clearly involved.
Sounds like a job for MythBusters 
It’s The racks?
I have always thoughr a canoe on top of a car without the arodanamicly messy racks and bars would be ideal,but I never was able to get the boat secured properly without racks.It moved in crosswinds and when trucks passed,so I went back to my rack.
Turtle
Like WWW says…
Changing the drag coefficient and velocity. You are definitely affecting CD. Would almost bet you are driving slightly slower with boats on top for safety reasons. Not all vehicles will be positively affected, some will suffer a CD loss.
It seems illogical at first. I have no doubt these folks are observing some gains, same as I do not doubt some folks will lose mileage.
Mythbusters would have to try an array of vehicles and canoe sizes. This would be pretty expensive but interesting. Just don’t let the Gov’t run the experiments or will lead to vast new regulations regarding boat and rack profiles and materials.