Gas mileage improvement when car-topping canoe(s)?

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I noted elsewhere that our Ford E-150 van (5.4L V-8 engine) recently got a steady 13mpg going cross-country with three tandem canoes on the racks. That is still effective for cost-sharing when carrying multiple boats and people on group or family trips, but not so much for long solo outings.

Looking at past MPG road trip records for the van it gets better MPG when carrying multiple kayaks or decked canoes, 16mpg or better with 3 or 4 decked boats up top.

I took a long solo road trip a few weeks ago carrying a single solo canoe on the van. That boat has 60” airbags for the bow and stern, and I put them in for the trip (your opinion about travelling with floatation bags in boats may vary; I don’t usually do so). The van averaged 17.4mpg. I deduce the obvious:
Kayaks and decked boats cause less drag than open boats.
Multiple boats cause more drag than a single boat.

And the theoretical:
Leaving floatation bags in the canoe(s) may help reduce drag.
Shorter boats (the solo I was carrying is 14’) catch less air than longer boats.

I suspect that the position of the canoe(s) fore and aft on the racks, and aerodynamic (or not) shape of the vehicle, has considerable impact on open boat air capture/increased drag. The boxy hood and windshield of the van forces a lot of air over the roof, and if that air is trapped by the open hull more drag must be created. The equally boxy and much shorter roofline CR-V (4cyl manual) drops MPG badly with even a single boat on the racks (from 23 to 19mpg average).

I’ve seen folks travelling with their boats fully encased in an exterior bag, and always assumed that such bags were largely used to protect pricier composite hulls and finely tuned racing boats from chips and dings during travel. They also seem like a PITA to deal with at the put in or take out.

I wouldn’t travel with my CCS covers installed on the canoe, but I bet occluding the airflow up into an open boat would be MPG beneficial.

If you drive to paddle enough any MPG improvement could provide a return on investment. Someone else can figure the math, but a 2mpg improvement times X number of miles driven with boat, times X price of gas, over X number of years would seem worthy of some experimentation.

Maybe a rigid panel, sized for the specific boat/vehicle rack, could be placed atop/between the crossbars and secured within the edges of the gunwale stops before loading. That might serve as as simple to install drag-reducing air deflector. The panel could hinged in the center (-) for easier storage when the boat and racks are removed

I’m curious if anyone has played MPG improvements by the occluding airflow into an open boat, adjusting the position of the canoe fore or aft on the racks, using a fairing, leaving floatation bags installed or etc.

I have seen one vehicle transporting a canoe more aerodynamically gunwales up; a poorly tied Coleman atop a minivan. In a NJ Turnpike rest stop. Just before an impending black sky pounding rain. We lingered long enough to give him lots of highway miles before the first time he hit the brakes.

I pretty certain that method isn’t my preferred MPG solution.
 
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Mike,

You stumbled on some of the proven concepts of aerodynamics, based uopn the laws of physics (laws....not guidelines!!)

Actually, if you were to orient your hulls similar to that of an airfoil, or airplane wing, you would experience the least drag for a given hull shape.

As such, I have been car topping my boats to take advantage of this phenomenon as well.

I now carry all of my boats with the keel oriented vertical, that's right, vertical!! Much less wind resistance, and I even gain some lift (similar to sailing)...
But, I do have to watch out for highway underpasses, anything less than 23 ft clearance causes me to reroute!!
 
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You stumbled on some of the proven concepts of aerodynamics, based uopn the laws of physics

I now carry all of my boats with the keel oriented vertical, that's right, vertical!! Much less wind resistance, and I even gain some lift (similar to sailing)...
But, I do have to watch out for highway underpasses, anything less than 23 ft clearance causes me to reroute!!

I got stuck once entering a parking garage at the El Paso airport. Not in the van but in a small mid-80’s Toyota pickup with cap and canoe. Part way into the garage there was a suspended bumper and pull off spot with a sign that essentially read “You apparently didn’t heed the sign that read ‘Six foot max clearance’, so use this phone to call for help dummy”

I dropped the coin yesterday on a new Toyota Tacoma and will be going to spec and order a Leer cap with Thule feet rails tomorrow. With 6’ of cap length and 4” of (access-cab) roofline I’ve got a lot of length to play with.

Now that I have discovered the basic laws of aerodynamics I may experiment with the best placement and arrangement of boat or boats. I tend to keep my vehicles for at least 10 years or 250,000 miles, and with some vehicles a large portion of that is hauling boats.

Call it 100,000 miles with boat(s) on the roof. If I could squeeze a 2mpg improvement by positioning the canoe in the most advantageous spot on the racks and occluding some open-boat drag by using a fairing, floatation bags, sheerline panel or etc, the cost saving are considerable.

100,000 miles at 20mpg = 5000 gallons of gas. At current/local $3.50 a gallon (and it won’t be that in 5 or 10 years) that’s $17,500 in gas.

100,000 miles at 22mpg = 4545.45 gallons of gas. X $3.50 = $15,909.

As gas prices rise that could add up to a couple thousand dollars over the years. I’ll be experimenting with boat position on the racks, fairing, floatbags or other air occlusion and keeping track of the MPG to see what works.
 
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Inaugural Tacoma Trip Mileage

One boat (Monarch), mucho gear:
25.36 mpg (inter-States north and secondary road into the Adirondacks)
25.53 mpg (secondary roads from the Adirondacks to northern Vermont)
26.10 mpg (mostly inter-State highways to central NH)
24.06 mpg – Secondary roads and dirt roads into the Rangeleys in western Maine.
23.95 mpg – Back out of the Rangeleys and across NH and VT, all secondary mountain roads.
24.55 mpg – More mountain secondary’s and a bit of inter-State

So I now have a baseline. I’ll be curious to see what the MPH is like with two boats, especially with open boats. And what the MPG is like with no boats/no racks, although that may be a more rare opportunity.

The Tacoma is exactly what I thought it would be; an awesome travelling vehicle. I brought two tents, two sleeping bags, a 5 gallon water carboy, large ice chest, 6 paddles, food for 30 days (30L barrel and two 3 gallon buckets), a half dozen stuff bags and more clothes than I would wear in a month.

I’ll be working on a few things; curtains for all of the cap windows, a better seal around the tailgate (it sucks in dust on dirt roads), maybe a deployable screen over the cap door for better camping ventilation and some kind of stuff bag storage system. I oughta have it further perfected in a few days of shop time.

I see another road trip in my future soon. You know, just to further refine the outfitting.

BTW – My initial query was about obtaining less of a reduction in mpg when toting boats, not about actually improving everyday mileage with some kind of rooftop deltafoil.

Although the “winglets” that commercial jets all now seem to sport might have some crossbar application. Thule needs to do some wind tunnel testing.
 
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That isn't bad at all.

Our Forester with one boat and 'mucho' gear gets about 26 mpg on secondary roads (speeds less than 60 mph) and about 23 mpg on the highway (speeds from 70-75 mph). That is with a 2.5L PFI, DICP engine with a CVT. Without a boat it is in the 27-30 mpg range, so a significant difference.

I too would think a cover over the deck would be beneficial for fuel mileage. Just a hunch though... there may be so little airflow due to the boundary layer being pushed up over the canoe that it may not make a huge difference.

Interestingly enough, and it somewhat makes sense, is that our sedan did much better with the boat on. We had a Jetta before our Subie and although it didn't do as well with gas mileage without the boat, the delta from with to without was much less. I suspect it had something to do with the boat not overhanging in the rear as much and creating vorticies. With the Forester you have a relatively flat back with the canoe hanging two and half feet off the back... I can only imagine the flow not being transitioned very smoothly in that sense.

It seems that if I am correct about that a longer vehicle, like a truck with a cap, would be less sensitive to the boat. I think though, that when you add two you are going to see a real decrease. My thought there is because they will being hanging over the side of the vehicle and disrupting the side flow (not to mention the obvious increase in frontal area). I will be toting two tandems on the Subie soon enough so I'll be able to see the real world effect.

BTW what engine is in your Tacoma?
 
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I think though, that when you add two you are going to see a real decrease. My thought there is because they will being hanging over the side of the vehicle and disrupting the side flow (not to mention the obvious increase in frontal area). I will be toting two tandems on the Subie soon enough so I'll be able to see the real world effect.

Having two boats on the roof racks will definitely decrease the MPG. I think the easiest way to ameliorate that mileage loss is to keep some space between the hulls, so that the air can pass between them rather than be trapped in the closed vee between the bows.

I have 78” Thule bars on the cap, spaced 43” apart, so I have plenty of room to separate the boats on the racks.


BTW what engine is in your Tacoma?

The engine is the 2.7 liter with an automatic transmission. My previous Toyota trucks both had manual transmission, but the 1 mpg difference in current model Toyota trucks was a fair trade for the driving ease of an automatic.

While the engine in the truck is certainly not the big 5.4L V8 in the Ford van when climbing mountain hills, it gets the job done and I don’t plan to haul a trailer

Toyota specs the 4-cylinder automatic MPG at 19/24, and the V6 MPG at 16/21. That was a big enough difference to opt for the 4 banger.
 
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I'm surprised that with all this gained efficiency, vehicles don't come equipped with canoes as standard fuel saving equipment mounted on them.

I know, I know, I'm just wishing. But just imagine ......

The salesman says, "Would you like the red Swift canoe or the yellow Wenonah canoe fuel saving system? Both give you increased gas mileage."

The buyer replies, "I'll take the red Swift canoe. Everyone knows that red canoes are always faster than yellow ones. And I want my vehicle to go faster."

I too noticed an increase in gas mileage on my old and long since gone small Hyundai Elantra wagon when I topped it as well. The roof slope with the racks made the back end of the canoe sit higher than the front. I am not an engineer and can't explain why that happened, I have no idea. But I know it did.

We definitely might be onto something the auto makers could cash in on.

The past ... Two cars in every garage.
The future ...Two canoes in every garage to save on fuel.

Sounds like a plan to me.
 
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I believe the going rate is about $30/% fuel economy gain... OEM cost. Given the current cost of canoes, the OEMs would need to double the FE numbers in order for them to be viable.

Very wishful thinking. And I'm really not BS'ing about that number. Less than a decade ago it was only $10/%. Honestly I can't believe it isn't higher.
 
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Hi Mike,

Is your Tacoma a 4wd? Mine (4cyl 5 speed manual, 4wd) only gets 20/21highway mpg, with or without the canoe.



Robin. It’s a 2WD. I was willing to sacrifice the 4WD capability for overall better mileage. I no longer face the occasional snowy commute to work and if my dirt driveway (up a long hill) looks to be forecast as impassible I’ll just move the truck to the top and park it there. Before we had a 4WD I hiked up the hill on snowy mornings for 10 years to get to my previous 2WD truck.

The photo of your Tacoma illustrates a cap dilemma. I had tall construction racks on my two previous Toyota trucks, and with flush height caps they still had ample height clearance so that the deck plate of the inverted canoe was still above the cap roof line.

I initially thought to put on a cab-height cap, figuring that it would present the least windage. But when I did the math on the sheerline rise on most of our canoes I found that I’d have to position them far forward of centered/balanced on the racks, and if I slid them on from resting \ on the back rack I’d have to keep a lot of the hull levered up until the stem cleared the roof and I could drop it down.

I went with a mid-height cap that is 4” taller than the cab roof. That additional 4” coupled with the height of the rack gives me enough clearance. I have 78” Thule bars on Tracker II feet, with 43” of spread between the crossbars, so I can get (if ever needed) two 17’ tandems on the racks with some air passage gap between them.

Those Thule bars and feet were repurposed from my previous vehicle, and I have some Yakima bars and feet that may fit as a third crossbar over the cab roof. I think I have enough bar width and cap/cab roof line to add a third crossbar over the cab doors and fit three canoes, one positioned forward in the middle resting on the cab crossbar and front cap crossbar, and two positioned outboard on the cap crossbars, nestled kind of like --=.

We nestle 4 canoes on the van (11” rain guttered roof line), staggered and taper-nestled two forward and two back on 4 crossbars.

As long as I can fit at least two canoes I can do my part on group shuttles, or haul a friend’s boat on trips. But if I could rack a third boat when occasionally needed that would be a boon.
 
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