Semi-truck Boat Tail Improves Fuel Efficiency 7.5%

I’m always for energy saving ideas when they payback the effort. Here’s one that would be an advantage for our long haul American Interstate trucking companies. This semi has both side wings and a boat tail to decrease wind drag.

It is pretty simple really:

‘Boat tail’ decreases fuel consumption for trucks by 7.5 percent

From a Delft Technical University press release

A boat tail, a tapering protrusion mounted on the rear of a truck, leads to fuel savings of 7.5 percent. This is due to dramatically-improved aerodynamics, as shown by road tests conducted by the PART (Platform for Aerodynamic Road Transport) public-private partnership platform.

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Here are the other places wind resistance on a semi-truck can be addressed for fuel savings:

semi-truck-savings

Click for larger image

Public highways

A boat tail is a tapering protrusion about two metres in length mounted on the rear of a truck. The boat tail had already proved itself during wind tunnel experiments and computer simulations, both conducted at TU Delft, in theory and using small-scale models. Now an articulated lorry fitted with a boat tail has also undergone extensive testing on public highways.

Emissions

An articulated lorry was driven for a period of one year with a boat tail (of varying length) and one year without a boat tail. The improved aerodynamics, depending on the length of the boat tail, resulted in reduced fuel consumption (and emissions!) of up to 7.5 percent. The optimum boat tail length proved to be two metres.

PART

The tests were conducted by PART. This is a platform in which academics, road transport manufacturers, transport companies and shippers work together. The platform aims to reduce fuel consumption in the road transport industry by improving aerodynamics. PARTs ambition is to achieve a 20 percent reduction in fuel consumption and CO2 emissions in the road transport industry by 2020. TU Delft acts as secretary of PART. PART has previously conducted road tests on a new generation of aerodynamic sideskirts, which are to make their commercial debut later this year.

More information

More on PART: www.part20.eu
More about the side wings: www.ephicas.eu

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136 thoughts on “Semi-truck Boat Tail Improves Fuel Efficiency 7.5%

  1. Dang! I could have thought of that! Oh well, it’s not the time to be concerned about money with the banking cartel and other dragons to slay. Now about that Princess …

  2. If they would use the railways more efficiently and just use local distribution from the railway system, they would not only make the whole moving of good more efficient but also make the highways safer. The big rigs are a real mortal danger to us little car drivers.

  3. Pamela,
    I was thinking the same thing, except I don’t have the (insert body part here) to drive that close to a simi. I want to die in bed – or anywhere else besides on the highway. I’m with Anthony, discoveries like this can save fuel, dollars, and lots of bad stuff from going into the air (soot, CO, the terrible GHG H2O, nitrogen compounds and so on) Work like magic, cost very little to install, and have a return on investment that is tangible.

    What a concept.

    Mike

  4. These are also impractical and add weight to the vehicle. The truck driver must stop, remove the boat tail, then back into the loading dock. After leaving the loading dock, the boat tail must then be re-installed. Each operation requires time, and time is money to a trucking company.

    There are also overall length limitations in the U.S. – the aerodynamic improvement device cannot extend more than 5 feet beyond the trailer. (23 CFR 658.16(b)(6)) Those that are 2 meters are just a bit too long.

  5. I see that everyone else beat me to the “drafting” issue. Ray (21:05:29) : is also partly correct about rail…. back in the 60’s I was a railroader and my favorite job assignments were to freight or switching (I also worked the commuter runs from Stamford to NYC and decided I HATED commuters)… but building a spur to a factory is expensive and trucking allowed you to build your factory/warehouse/distribution site anywhere the land values and taxes were cheaper. The completion of the Interstate System in the 70’s drove the last nail into heavy-rail freight. Pity.

  6. Ray (21:05:29) :

    If they would use the railways more efficiently and just use local distribution from the railway system, they would not only make the whole moving of good more efficient but also make the highways safer. The big rigs are a real mortal danger to us little car drivers.

    This also would have the added benefit of putting all interstate shipping in the hands of the unions.

    By the way, most rail lines which are government subsidized lose about $35 per passenger.

  7. I’m with Ray. Railways for heavy goods. Trains can be made very aerodynamic too, especially with top & side sheets between the cars.

    Aerodynamics tends to ruin slipstreaming, (draughting/drafting).

    DaveE.

  8. The stickers plus the box total 28.7% gas savings. Sounds too good to be true. Notice the “up to” that has been left out in the first three paragraphs, then slipped in towards the end as an afterthought. My BS detector has gone nuts.

  9. It would reduce the efficiency of drafting behind a big rig…….but probably only very slightly. This sort of addition to big rigs will be difficult to implement in practice…..there are very very strict length limitations for the various types of axle combinations in North America. Also, a huge part of trucking in general is to be able to easily back up to a loading dock, quicklly & repeatedly throughout a typical day.
    This modification would appear to impede that somewhat & it would have to be detachable, which is further inconvenience drivers don’t need or want. If you actually built it into the shape of the trailer the rear doors would be too small to be functional. It’s a tough design problem.

  10. They could put a screen back in there and project “An Inconvenient Truth” in an endless cycle. You know, to educate the driving public. Just and idea.

  11. This is why I like this site – there’s always something interesting going up.

    Ray said:

    “If they would use the railways more efficiently and just use local distribution from the railway system, they would not only make the whole moving of good more efficient but also make the highways safer. The big rigs are a real mortal danger to us little car drivers.”
    If it were cheaper to move goods as you say, then the distribution companies would do so. One can’t just second-guess hundreds and thousands of folks whose livelihood in on the line.

    Regarding the trucks being a danger . . . well, that’s why I like larger cars.

    Craig

  12. You could do much the same with a canvas boat tail that would self-inflate with speed, and wouldn’t damage anyone who rear ended it.

    Those small spoiler wings that station wagons use to keep the dust off the rear window would reduce drag, too, though not as much as a full boat tail.

  13. The B-triple road trains in Australia always fascinated me. I guess those must be highly efficient. One tractor pulling 3 loads.

  14. Imagine that rig in snow, ice, side winds, or getting max cargo under the length regulations. I’ve got a half million miles long haul driving and I can tell you that rig is a looser.

  15. This is old news. I remember reading about a rubberized fabric boat tail inflated by the tractor air system when the rig was on the road.

    All of these have the same problem. State law sets limits on maximum rig length. Adding a 2 meter boat tail under current laws requires eliminatig 2 meters of trailer. The loss in cargo capacity costs more than the fuel saved,

  16. Oh I can just see it now. The boattails will be getting ripped off while maneuvering at truck stops, shippers and receivers and rest areas. Likely many front tractor hoods will taken off as well. Can you see one of those things trying to turn hard in a Wal~Mart parking lot and taking the top half of your vehicle off. Its just nuts, and the fairings are as well… try putting snow chains on one of those puppies with all those fairings and stuff. Now a good engine design and gearing on a truck with good nose configuration can meet or likely exceed the efficiency without all the bodywork in the shop.

    Freight rates regulated to where companies can afford to install new air filters, more frequent oil changes, new tires, (not recaps) and improved maintenance & inspection would do far more to reduce fuel usage than this silly idea.

  17. The other advantage of railways is lower rolling resistance, though with modern high pressure tyres, (tires), I’m not sure how much of an advantage this would be.

    Perhaps an efficient rail network isn’t practicable in a country as large as the U.S.A. whereas in the U.K., it’s just not practiced ;-)

    DaveE.

  18. Oh I can just see it now. The boat tails will be getting ripped off while maneuvering at truck stops, shippers and receivers and rest areas. Likely many front tractor hoods will taken off as well. Can you see one of those things trying to turn hard in a Wal~Mart parking lot and taking the top half of your vehicle off. Its just nuts, and the fairings are as well… try putting snow chains on one of those puppies with all those fairings and stuff. Now a good engine design and gearing on a truck with good nose configuration can meet or likely exceed the efficiency without all the bodywork in the shop.

    Freight rates regulated to where companies can afford to install new air filters, more frequent oil changes, new tires, (not recaps) and improved maintenance & inspection would do far more to reduce fuel usage than this silly idea.

  19. Do you folks have any idea how much freight is moved in this country? If railroads could move it all, believe me they would be doing it. But rail is lacking in capacity and slow… manufacturing and retail/wholesale demands ‘just in time’ delivery for the most part, so that they do not have the expenditure of vast warehouse storage. Fresh fruits and vegetables as well as most meats cannot take a long time to move from point A to point B.

    Even if rail had the capacity you will still see the same numbers of trucks, they just won’t be doing the long haul. Go check out how many warehouses have rail docks yet get the majority of product through the truck docks. There is a reason for this… just in time, triple screamer hot loads. Companies often do a poor job of ordering product because they run down-sized on staff and fail to spot shortages effectively.

  20. Doug (22:10:11) :

    Imagine that rig in snow, ice, side winds, or getting max cargo under the length regulations. I’ve got a half million miles long haul driving and I can tell you that rig is a loose

    A few years back, I was hitch hiking & got a lift in a 40 ton curtain side from Kings Lynn in Norfolk, (U.K), East Anglia is flat & largely below sea level. Winds were gusting to 70 – 80mph & the lorry only had 4 tons on board.

    It was an exciting ride LOL

    DaveE.

  21. Ray (21:05:29) :

    Which is why George Soros put his money in the railroad. He knows where the top efficiency in land transportation lies.

    DaveE (22:17:11) :
    Oh, but rail is very practicable in the US, especially given the distances involved.
    Before the advent of cheap fuel, rail was already king of overland efficiency.
    Now that cheap fuel is fast becoming a distant memory, rail is commanding attention.

  22. Here in Australia we have the worlds most efficient road transport.

    When I used to cart ammonium nitrate to Telfer years ago with 4 unit road trains I found the wind direction made a huge difference to speed & fuel consumption.

    If you were going directly into the wind the trailers would slipstream each other.

    However if you got a strong north easterly of the desert is would hit every trailer and drag you right back sometimes where you spent hours doing 40-50km / hr.It took 6 1/2 hours to do 255km one night.

    A bit like a surf cat going fastest across the wind in reverse.

    Of course they are spoilt now with a couple of hundred horsepower more than We used to have.

  23. Ray (21:05:29) : “If they would use the railways more efficiently . . . ”

    Warren Buffett’s Berkshire Hathaway Corp. just bet big time on your very statement. $26.3 billion. See:

    http://online.wsj.com/article/SB10001424052748703740004574513191915147218.html

    I don’t know what that trucking-boattail costs but a 7.5 % fuel savings ought to be recovered in a short while. That will be a big savings in dollars and diesel fuel over a year’s time.

    Good work, I say. But they need to add a screen over it or folks will be jumping in for a free ride – then falling out and suing someone.

  24. Eddie Murphy (22:40:56) :

    I don’t get this slow bit.

    Trains should be able to move freight faster than road transport, much faster! A train should be capable of 80mph+ on a long run.

    DaveE.

  25. British bus companies used to (Don’t know if they do still) mix water with diesel to reduce fuel consumption. I believe it worked quite well, but I don’t have any information about it.

    Also, another factoid, is that round cornered roofs on trailers like this reduce drag and improve stability in high wind situations.

  26. AndrewWH (22:55:45) :

    Can’t see them being any higher than those John Lewis Partnership triple decks.

    DaveE.

  27. “These are also impractical and add weight to the vehicle. The truck driver must stop, remove the boat tail, then back into the loading dock. After leaving the loading dock, the boat tail must then be re-installed. Each operation requires time, and time is money to a trucking company.”

    Good point – but one wonders if it couldn’t somehow be hinged so that the sides flip forward along the side of the trailer and the top up, laying on top of the trailer. Not sure about the bottom.

  28. General Aviation and Gliding spend bucket loads on drag reduction from surfaces. Dennis Conner in the Americas Cup (about the last time it was Americas!) used a drag reducing surface on the cup winning boat.. There are a lot of these airflow controls used in these areas that would be much lower impact to control turbulent airflow if an engineer thought outside the box!

  29. DaveE (22:57:37) : Eddie Murphy (22:40:56) : I don’t get this slow bit. Trains should be able to move freight faster than road transport, much faster! A train should be capable of 80mph+ on a long run. DaveE.

    In just a few areas, they can. But trains often have to wait for tracks to clear and also wait to get into a rail yard to load/unload.

  30. Running a railroad is not quite as easy as one may think. Back in the “old days” the Naugatuck Valley was an industrial power house and all the factories had spurs and sidings for rail delivery, but it was a single track main…. scheduling and timing were everything. We could deliver reliably, but it was our schedule, not yours. A through train might drop off fifty cars in our yard and pick up 45 to take up the line, but we then had to sequence those cars for each of our deliveries, wait for the main to be clear so we could move them up to the sidings…. and then move them. On the Naugy line we had a lot of grade-level road crossings, and many of the spurs and sidings were actually along streets. One of my best memories was on the Derby Switcher moving a drag into position at a rubber factory in Shelton. Some trucker started beeping at us to get out of his way. Our engineer nuttered… “mine is bigger than yours…” and gave him a blast of the air horn that damn near blew the semi off the road.

  31. rbateman (22:44:36) & J Hulquist,

    Soros and Buffet didn’t “bet” on rail vs trucks as suddenly being more efficient; the economics of that equation have been relatively static for some time. Any “recent” bets reflect their opinion that the economics are about to change. Think “cap and tax”, and get ready to be poorer as governments mandate that everyone tithes to Gaia, with themselves as middleman.

  32. If those boat tails are not well maintained I think there will be problems. Bad enough driving past a flapping curtain. I would hate to be anywhere near a flapping boat tail.

  33. Have a look at this Mercedes Truck from Colani, also look at the tail end of the truck
    We know how to apply aerodynamics but regulations and efficiency requirements reduce the possibilities. Take a standard 20″ foot container and you have ample lenth available to put a flat nosed truck in front of it.
    Not much room for thinking out of the box if you are in the business of container transport.

    Google Colani for other breathtaking designs

  34. DaveE (22:57:37) :

    Move faster? Yes and no. Freights are usually hauled by diesel, slow to spool up but they have the torque to move huge loads. They need a good, level straight-away to move. Curves, like we have in New England, or grades like they have in the West, significantly reduce speed. (even the Acela, an electric high-speed passenger train running from DC to Boston, still runs at about 50 mph once it gets into New England. Too many curves.) Freight trains are more economical the more cars you can attach…. but a mile-long train will take more than a mile if it needs to stop. Even in the computer age, rail lines are regulated with a “block system”, a train usually may enter a block if it is empty. If it is not empty, i.e. there is another train believed to be ahead at an inknown distance, the train must proceed at a significantly reduced speed, prepared to stop if there is a chance of collision.

    Me, I’m a computer geek who really doesn’t trust computerized rail traffic control systems.

  35. Just what we need to make our highways safer. These, and those new-fangled electric maiming and death can’t-see-the-damned-things traps.

    My entire career mostly as a highway engineer is about to be wasted entirely. I do have to wonder exactly why we, the taxpayers, paid so much to make our highways safer to drive on. It obviously was money wasted entirely.

  36. And that duck-tail…. if it reduces the drafting effect, what does it do to turbulence? Trying to pass a truck gets a bit hairy once you pull even with the cab…

  37. Here is another aerodynamic application featuring the overhaul of a standard Honda Civic. I admire the initiative and I see the driver clocking high way miles with a smile on his face, until has to park it.
    http://www.aerocivic.com/

  38. I saw, on the Drudge Report the other night (it was only there for about a half hour before it was removed) a report from one of our very own federal government departments, which said that the United States has, as a nation, more energy reserves than any other nation on the planet. About 1.3 TRILLION equivalent barrels of oil, in crude oil, natural gas and coal. Known and obtainable reserves. Russia came in second with about 1 trillion equivalent barrels of oil.

    We are quickly being destroyed by humankind’s oldest enemy . . . simple greed.

  39. Doug (22:10:11) :

    “Imagine that rig in snow, ice, side winds, or getting max cargo under the length regulations. I’ve got a half million miles long haul driving and I can tell you that rig is a looser.”

    7.5% savings would seem significant, and of great interest to truck companies. But there would be costs associated with this tail, and I doubt that the numbers would add up to any savings overall. But the intent here appears not to be for economic benefit, but: “to achieve a 20 percent reduction in fuel consumption and CO2 emissions in the road transport industry by 2020.”

    Regulations can be changed (and some will) and companies will pass on costs to consumers and keep government “incentives” (unless the government gets into the business of price/profit fixing). Arguments could and may be made that make it appear that the obstacles you mention could be minimized or eliminated by either design or practice. But the one I doubt could be overcome is putting a tail rudder on an 80 foot long haul rig. The website says that drivers would have be “educated” and “will need [to pay] attention” to wind effects. Holy cow. A big handwave there IMO. Perhaps trucks could be fitted with articulated wheels, so they could crab in the wind like airplanes. Seriously, improving road surfaces and conditions, better tires and other measures would likely improve fuel consumption more than a nickel a mile.

  40. This is killing a fly with a machine gun. Take a look here: http://www.meridian-int-res.com/Aeronautics/Coanda.htm – and scroll down until you come to a simple solution by Robert Englar exploiting the Coanda effect. I imagine Pamela would still be able to slipstream and Roger Sowell would still be able to back into his loading dock and get at the rear doors.

    What Ripper describes happens with fully streamlined trains too, the problem is with side winds.

  41. Alright, longer trucks, strange constructions protruding from the rear, just what we need on the already crowded highways in the “Randstad” (the for largest cities in the Netherlands).

    And longer trucks, wait until they get off the highways and have to navigate roundabouts, speed limiting obstacles like speedbumps and chicanes and other devious devices that civil servants and city councils can think of.

  42. Roger Sowell (21:13:20) :
    ……………….
    “There are also overall length limitations in the U.S. – the aerodynamic improvement device cannot extend more than 5 feet beyond the trailer. (23 CFR 658.16(b)(6)) Those that are 2 meters are just a bit too long.”

    All European long haul trucks are cab-over, making them shorter then the common American trucks to begin with.

    An expanding-contracting rear of the trailer is not a big design problem.
    I say, just go for it!

  43. Thanks to AndrewWH. There are a few points I would like to make, coming from the same manufacturer that makes the Teardrop trailers.

    http://www.donbur.co.uk/gb/products/aerodynamic_teardrop_trailer.shtml

    Firstly, boat-tail fins have been proven to work well, and further research from DERA (UK Gov Research) or “QinetiQ” as it is now known, has shown similar improvements to fuel economy.

    As pointed out in many posts here, the rear of any trailer is subject to heavy stresses and any protruding object is likely to get ripped off in the first couple of months of service. As standard, we like to manufacture clutter-free rear frames.

    Unfortunately, any aearodynamic aid that is added to a trailer is vunerable to damage and maintenance costs can far exceed any aerodynamic savings you may make thus making the whole concept unviable.

    There are a number of additions we are considering, including the elimination of the tractor-trailer gap and skirting improvements, but all have to be durable, cost-effective and, more importantly, they have to provide a payback period of less than max 3 years.

    Just to give you some idea how much CO2 trucks/trailers emit, try out our CO2 calculator @ http://www.donbur.co.uk/gb/carbon_emission_calculator.shtml

    considering one trailer might do say 60,000 miles per year at maybe 8 mpg, the fuel cost and CO2 output is frightening.

  44. Yes, we are the Saudi Arabia of natural gas and there have been enough new oil finds, with improved drilling techniques, that gas should never go above $2 a gallon. But it is… Greed?

    Ray (21:05:29) : ….also make the highways safer. The big rigs are a real mortal danger to us little car drivers.

    A: Actually truck involved accidents continue come down with the new 10 hour break in the hours of service rule.

    B: I’d say 80% of the time the reason trucks push so scary hard has more to do with the infrastructure and greed supporting the driver than the actual driver. Load planners who book too many loads and wait until the last minute to broker the load out to a company that can haul it when they see they cannot cover it.
    Shippers/manufacturers who have an order to be delivered on a scheduled date dilly dally around and it gets shipped at the last moment. Dispatchers who don’t get the freight moving, forgot about the load. Receivers who won’t take responsibility to unload their freight in a timely manner, leading to late pickup of the next load. Driver unloads instead of hiring the expensive in-house lumper service and therefore gets penalized, maybe has to come back the next day. Drivers know that if the load is late the receiver will likely penalize them and make them unload at a later date. Take good ‘ol neighbor Wal~Mart for example, if you are 1/2 hour or up to 1 hour late the load has to reschedule for the next day or so. On and on it goes, I could write a book.
    C. The little car drivers are a hazard period with so much inattention.
    D. Bad railroad crossings kill good skilled drivers.

  45. It’s a lift and swing issue, from a practical point of view for the load and unload, length is a legal issue.

    In Australia we have road trains in the centre, that measure 3 times that beastie in length.

    The back fairing does not have to be heavy just aero dynamic/.

  46. Remember those ‘spoilers’ that popped up on the wing surface of the 707’s as they came in to land? An Australian firm marketed a similar set of small angled wings that fitted to the rear sides and top of trucks and autos. and claimed up to 10% fuel reduction, by ‘laminar flow improvement’.

    I made up a set and fitted them to the 92 Subaru Wagon and at least it keeps the rear window clean, does improve the mileage, and makes it a breeze to find it in a car park!

  47. One last thing I used to be involved with heavy transport. And yeah I know a bit about Australian truckers. If that ugly fuggin thing can get 5% fuel economy. It will work for them. I have never met long hours in small business like they do.

    One truck and a contract, and fuel is their demon nightmare. Maintenance their second, and the third one is plant legacy.

  48. My brother has a Kenworth Conventional, mounted under the front of the truck is a wind deflector that is mounted on a hydraulic piston which has a reach of 3 feet, which he can extend at will, he says that it gives him ( on the open road) an extra 2.5 to 3 miles a gallon. He also has an ex military aircraft oil cooler mounted before the turbo and an air cooler ( from the same aircraft ) after the turbo which maybe one of the many reasons that his 600hp gives him a compact car economy,

  49. Michael J. Bentley:

    [i]”I want to die in bed – or anywhere else besides on the highway.[/i]

    Amen to that!

    I want to die like my Grandfather, in his sleep. Not screaming and swearing like his passengers…….

  50. DaveE (22:57:37) :

    Eddie Murphy (22:40:56) :

    I don’t get this slow bit.

    Trains should be able to move freight faster than road transport, much faster! A train should be capable of 80mph+ on a long run.

    Another significant delay with railroads is not “getting to the other side of the state (or country even)” but “stopping and backing and breaking up the train cars to get the specific one or two cars needs for each different customer moved off the main line, stepped in front of the right door at the warehouse, and re-connecting the train to go to the next warehouse and doing it all over again.

    If it takes 30 minutes to drop of two cars and get moving again, you can only make 8 stops (drop offs or pickups) in an entire morning. And the last customer gets his rail car at 12:00 – when eh may or may not want it, and the first customer gets his at 8:00 – when HE may or may not want it.

    In the meantime, the rest of these 8 warehouses are getting 120 or 200 trucks in AND OUT at exactly the right time they want their specific cargo loaded or offloaded. Need space? Park the trailer in he parking lot for a few hours (or days.) Need only a little bit unloaded – do it. You don’t need to call the entire train back to get three boxes send early.

    Best economy is free market: let the customers decide what THEY need for the best price.

  51. I would also like to point out that there is ~ 8% difference between the best & worst on a modern diesel’s BSFC (brake specific fuel consumption ) curve which is measured in lb’s per BHP per hour.

    So if you drive and keep the revs as close as practicable to the optimum BSCF point you can make real fuel savings for minimal loss in travel time.

  52. Back in the 1950 they experimented with an inflatable boat tail, it worked well, but was difficult to inflate after every stop.

  53. My father was a truck driver as well as a private pilot. I remember discussions with him on this same subject 25 yeas ago and his comment that a bullet would be more efficient if it flew backwards.

    It would have the basically the same surface area facing forward and wouldn’t have the drag due to turbulance behind it.

    Note that it might be just a bit less stable, though ;)

  54. Greetings, I’ve followed this site for quite a while, and finally a subject I have some personal experience with. I work in the service department of a small trucking company in northern Wisconsin.

    Improving fuel efficiency is one of our constant challenges. We constantly monitor and try to improve the way the trucks are operated to attain our best fleet average. The things that helped the most are limiting idle time, and lowering the governed highway speeds. Slower speeds = fuel saved! You will notice many trucks in North America that travel slower than the cars one the highway and this is one reason why.

    Many products come with a claim of a certain percentage of improvement, but they just do not work out in real life situations. Sometimes it is just because the actual time spent at highway speeds is less than the time spent in town, at slower speeds, making deliveries, dealing with traffic congestion, bad weather or any of the other daily problems of the trucker. If the truck is traveling at less than 30 mph, what will the boat tail do for fuel efficiency?

    I’m sure some of these ideas will help in the design of new equipment, but they must pass the test of practicality in the real world.

  55. Alvin (22:03:08) :

    Why is this a good idea? Because it saves money.

    In business, that should be the one and only motivation. But in Warmland, the motivation instead becomes “saving energy”, and, ultimately, “cutting carbon”. The actual costs are never mentioned. Why? Because again, in Warmland, those aren’t the motivation. Think about it. If trucking companies wanted to save money, don’t you think they would already be doing these sorts of things?

  56. I tested a similar model in our wind tunnel some years ago. Drag was significantly reduced. One of the problems that the student pointed out in his report was that braking efficiency was also reduced.

  57. Rather than the tacked on boat tail, couldn’t you just have the rear doors shaped like \/ rather than — ?

  58. Boat tails on semis are nice, amen! They’ve been tickling my brain for twenty years… But consider this: how much longer of pavement will get occupied on bumper to bumper urban highway in the city? Anything that takes more pavement lenght decreases traffic swiftness as soon as the traffic significantly slows down, e.g. when there is less than around two-three seconds of distance between cars. If you like your present traffic jams, wait till you try to save 5% of fuel on a few semis… You will have thousand more automibiles and trucks idling along in urban traffic jams, each costing opportunity time, and fuel. Opportunity time might be the biggest cost of all, decreasing quality of life.

  59. Let’s talk to independent truckers. They own the tractor but not the trailer. They pay their own fuel costs. So why would a company make a capital investment and then pay for additional maintenance costs to save an independent trucker money on fuel costs? I do not know what percent of trucking is done by independents, anyone?

  60. Roger Sowell (21:13:20) :
    “…impractical…The truck driver must stop, remove…re-install…time is money…”

    This was just an experiment to test the aerodynamics in real-world conditions. In practice, I’d think you would design the boat-tail into the trailer by tapering its rear 2 meters. Of course, you’d lose some cargo space, and you’d need to be able to open out the sides to accomodate large cargo, etc. The real question is whether the fuel savings would offset the reduced revenue and added complexity of the trailer. 7.5% savings on fuel is a pretty big chunk.

  61. Do you folks have any idea how much freight is moved in this country? If railroads could move it all, believe me they would be doing it. But rail is lacking in capacity and slow… B.

    … just in time, triple screamer hot loads. Companies often do a poor job of ordering product because they run down-sized on staff and fail to spot shortages effectively. – Eddie Murphy

    Ed “Just in time” is also about eliminating complete warehouses. R/R just do not cut it in efficiency. My ears still ring with the swearing from the warehouse foreman and production manager when the R/R did not bother to move our load from the flat bed to the truck for a week and no amount of screaming got us anywhere. The company would rather pay a slightly higher transport rate than shut down a production line for a week because the R/R will no get off their duffs and move a load siding on a rail siding.

    Fuel efficiency could be greatly increased by redesigning trucks completely such as a V shaped snout, a smooth shroud connecting the cab and trailer and the boat tail. Unfortunately it increases the length. With sleeper cabs and 53′ trailers the laws, roads and especially the loading dock areas just will not take longer rigs.

  62. The biggest problem with railways is the monopolies they impose. Unions take over and employees don’t ever have to worry about competing and service. Roads represent the free market.

  63. Guys, the cheapest way to move stuff is a ship, hands down by a signicant factor. Unit BULK shipping is the best – you can stick 200,000 tonnes of cargo in one ship and GO.
    Containerized ships aren’t bad either.

    The second most efficient way to move stuff in $/tonnne/Mile is a “unit train” that something like 100-150 cars of one product like coal. Again containerized loads aren’t bad either if you can move whole bunches long distances.

    (Way down at the other end are jet flighters on afterburner – possible the most expensive way to move something ever devised, though payload to orbit rockets are worse.)

    Ok.

    But $/tonne/mile is not the only thing. A personal car is not effiicent in that regard, but most of us are willing to pay for the convienience because the altnerative is the cost of messing around with public transit – iff’n you got it at all. and wasting TIME.

    Same way trucks are pretty efficient because they do things , as other’s have pointed out, in a time efficient manner. (Same thing with jet fighters really, costly, but the cost of not having one can be your life, so pay up.)

    The revolution of efficiency that shipping containers have been is difficult to over state. It allwoys shipping co’s to treat cargo as if it it were a unit ( nevermind waterproof/pilfer proof) so you can send and entire train/boat of “stuff” to distribution centers en masse, not mess with it at all, and allow trucks to do the “last 10/100 miles” efficiently like they do best.

    Also depending on your population density building a road and driving trucks on it represents a *LOT* less capital investment on infrastructure than laying track which if you have low volumes makes $$ sense.

    (Personal moving co’s are finally recogizing this too, with a slightly flimsier box.)

    Re:Drafting: there was an interesting show on TV (Mythbusters) that did an episode on drafting with cars on a track behind a large truck, it was really quite shocking how close you had to be to have a useful/measureable effect. ( Think 30cm/12″ or less. YIKES.)

  64. As Roger Sowell (21:13:20) pointed out, it is impractical, but Gareth (05:09:58)’s suggestion might be modified to work somehow, surprised that an adjustment like shape of the rear end has not been done yet.

  65. Luboš Motl (00:12:31) :

    “I trust you but it’s surprising to me: the boat tail looks like the ultimate birthplace of turbulence and whirlpools to me. ;-)”

    Lubos, from my aerodynamics courses (back before the jet age), it is true that the turbulence and whirlpools will be formed behind the boat tail. But the area of eddies and whirlpools is reduced from that of the truck sans boat tail. Also, extending the boat tail doesn’t necessarily achieve greater drag reduction, since separated flow will still occur at some point (but I’ve long ago forgotten how to calculate it). I wonder if I still have Hoerner’s book on aerodynamic drag stored away somewhere. ;-)

  66. (US perspective)

    Several posters have pointed out how some modifications to trucks won’t work with existing infrastructure and laws. Well, the laws could be changed, but there would need to be significant changes made to existing infrastructure to accomodate modified trucks. Examples: bridge clearances might need to be increased, docks might need extendable/retractable ramps, intersections might need to be widened for larger turning radii, etc.

    I wonder; how much fuel would have to be saved to offset the fuel expended to make the necessary infrastructure modifications? What’s the payback period in terms of fuel?

    I’ve been enjoying the links to various solutions that show how hard the private sector is working to solve the problem. (Thanks to all. Great links!) It’s not as though fuel economy is under the radar in the freight industry.

    As for me, I think I’ll save my pennies and try to get one of those Bentleys with a boattail instead of a boring ol’ Prius. I’m just certain my wife will go for that. How could I be wrong?

  67. Ray (21:05:29) : et al

    If they would use the railways more efficiently and just use local distribution from the railway system, they would not only make the whole moving of good more efficient but also make the highways safer. The big rigs are a real mortal danger to us little car drivers.

    True. Except there is not sufficient capacity to move the freight by rail, and with fewer trucks, who’d pay for the highways?

  68. Boat tail design has been in use with rifle bullets for many decades now. The increases in efficiency and bullet stability has made any other type extremely hard to find.

  69. Somewhere in America, a well intentioned bureaucrat is working feverishly on drafting legislation that would make these suggestions law. Of course, he is doing so without contemplating all the unintended consequences, and would never consider the fact that if this remodeling bears any significant economic merit, it will occur naturally at the insistence of the industry itself. If it proves inefficient for truckers to implement themselves, it will be bureaucrats that are forced to take action.

    It is the American way.

  70. I would think a reasonable implementation would involve a rail system not unlike automatic side doors on mini-vans. At least the top and two sides could be slid into place using rails. Could be completely automatic with the push of a button and only extended at higher speeds.

  71. This is excellent news. What does it look like and cost? I may have some pictures not coming through my filter.

  72. Nobody mentioned the recent Mythbusters’ episode where they “dimpled” the surface of a car, like a golf-ball. The dimples looked around 6″ dia & maybe ~1″ deep.

    The results showed significant fuel savings (can’t remember how much). So right there’s a relatively simple means of reducing air friction.

    Yes, I realize “dimpling” a car or truck’s body might have manufacturing issues in addition to aesthetic ones.

  73. I can envision this on over the road trucks running between terminals. The terminal yards, which are typically just of interstate highways (in US), could remove the tail by forklift prior to the truck backing to their dock and reattach to trucks heading to another terminal. It would make no sense on a local truck.

    I have a good friend who works for a truck mfg. and they are very excited about the 2010 truck models coming out with SCR (selective catalytic reduction). These engines are more efficent than EGR systems but have greatly reduced emissions. According to him, 65 2010 trucks generate the same emissions as one 2004 model.

  74. Having worked the logistics field for a number of years and, as can be seen in the many comments above, one size does not fit all. The whole business is a lot more complicated than most people would imagine. All the bells and whistles of aerodynamic fuel savings might work well for an over-the-road (OTR) shipping company that owns its fleet of integrated tractor/trailers. For the less-than-truckload (LTL) firm [such as YRC – formerly Roadway & Yellow Freight], a different mix would be in order. They might use one type of tractor/trailer combo to ship from Atlanta to Chicago, then, in the insane chaos of their destination terminal, transfer freight from a long-haul trailer to a city trailer which would be a simple “classic” tractor/trailer rig without all those fuel saving bells & whistles. And then there are the independents who would absorb some increased fuel costs while offering a less expensive alternative to the shipper. And then there is that other breed, the 3PL (third party logistics provider), who may offer warehousing/shipping services to smaller companies, by putting a number of companies under one roof so they can all realize the savings the 3PL offers. And that’s just the tip of a huge and complex industry.

    And then along comes some fantasyland bureaucrat with visions of implementing fuel savings ideas nationwide, and the biggest thing he’s driven is his desk. Okay, I’d humor him and might listen to his ideas after he’s driven a 53′ rig on a city delivery run (including backing that thing up to a loading dock straight and in under three tries) and can pick up a dime off a concrete floor … using only the forks of a lift truck.

  75. Richard Owens (00:59:18) :
    “considering one trailer might do say 60,000 miles per year at maybe 8 mpg, the fuel cost and CO2 output is frightening”.

    You really love the drama, don’t you Richard Owens.

    Remember this:
    CO2 is not a problem. It’s plant food. The greenest trees can be found next to the highway’s with the biggest traffic jams.

    Just face the reality. This whole “CO2 is frightening” act serves an ideological driven crowd who have totally different plans for humanity than you and me. Besides that, it will push the costs for distribution much higher than they are already without any sound scientific grounds.

    Even with the high fuel prices, distribution costs hardly play a role in consumer prices.

    The problem is with the independent truckers who drive the cargo based on fixed contracts. When fuel prices go up, they pay from their own pocket.

  76. Off topic/delete when reviewed: Putting a “Boat Tail” on the Tips & Notes page would significantly cut AGW caused by computers overheating waiting for the page to open. Last count there were 10,247,654,386,456,782 entries that had to open before you could make a comment.

  77. Anyone with a good engineering background will realize that with Reynold’s numbers below 2000 (typical for less than about 90 MPH on a truck!) the primary air resistance is ram air against the cross section.

    What many engineers might forget is that the “shedding vortex” on the back of the truck creates a vacuum, which adds a “parasitic drag”.

    Pamela Grey is quite correct, “Damn, there goes my free ride!”. I was with a friend 10 years ago, and she had a milage readout on her SUV. We were driving from Duluth to Mpls. It was a “no wind” day. I explained the parasitic drag vacuum phenomenon. We experimented moving in and out of the vortex shedding. Indeed milage went up by about 20%, when you were about a car length behind a “big rig”. Two car lengths you were still in the “wind shadow”, 3 to 4 car lengths you could feel the buffet of the vortex.

    Wind shadow gave about 10% better milage, and vortex buffet zone. Nothing.

    However, it should be noted: Driving 1 car length behind a “big rig” is NOT, repeat NOT a wise idea!

  78. I remember reading about these trailer-stream,lining schemes back in the late 60s. The terminal problem then was that the overall length of the vehicle was set, so streamlining had to be done at the expense of cargo space. The economics at that time were that it was cheaper to use more fuel and gain the extra capacity. The increased cost of fuel may alter the balance of costs.

  79. Ray (21:05:29) :
    -ot-
    “If they would use the railways more efficiently and just use local distribution from the railway system, they would not only make the whole moving of good more efficient but also make the highways safer. The big rigs are a real mortal danger to us little car drivers.”
    I have worked as a professional Driver as well as a Pilot.The Eighteen Wheelers are ,
    for the most part,not the problem.If you understand the dynamics of momentum,
    and the need to simply get out of the way,like a truck tailgating you because you are
    in your Pious,exactly at the speed limit(or below) just as a long grade is coming up,
    the Trucker has to preserve momentum uphill-just dropping a couple of gears more costs in fuel and time-all money.It is not an easy way to make a living.
    Having been on the other side of the steering wheel, I understand.
    -subject-
    There was a similar experiment done back in the 70’s that worked, but nothing came of it as they had problems with dings and dents,also certain states, had
    arcane laws about trailer length (Oregon was one.)…

  80. It sure seems to have taken these guys a long time to figure this out.

    Who can forget the works Porsche 917 Long Tails beating the Gulf/Wyler (sp) more conventional 917s at Le Mans back in the late ’60s or early ’70s ?

    Also I remember my friend’s ’62 VW Bus & backing right off the throttle 40′ behind semi trucks traveling up & down California on ‘Old 99’. Eventually, he over revved & blew the engine (36 HP !) doing that when behind a real cruiser of a truck driver doing 75 – 80 mph !

  81. Fuel savings from trucks are nothing new. Just down the road from were I grew up, a very small (5 truck) company owner designed the most efficient truck ever. This was in 1971 and it looked like this.

    As Dean H, writes, it was 40% more efficient than others at the time. Later models still work well. He had a real problem getting it sold, as truckers didn’t like the looks. Went on to work with Ryder trucks and make more improvements.

    http://www.paymastertruck.com/DNN47/Info/LaterModels/tabid/86/Default.aspx

    Confirms that there is nothing new under the sun, and especially on TV.

  82. Ron Dean (10:01:26) :

    “This idea is around 40 years old. NASA did a study on trucks in the 1970s, and concluded the “boat tail” was the optimal design for wind drag. The study went no where though – until now.”

    http://www.nasa.gov/centers/dryden/news/FactSheets/FS-100-DFRC.html

    Many drag reduction tricks have been adopted in newer trucks, but for some reason this boat tail is left in the dustbin. There are many articles, patents even, on the idea from over the years. I may be wrong, but I suspect it makes the rear end squirrelly under certain conditions. I can’t help but think that were this to save a lot of money and not kill people there’d been long ago all kinds of truckers and companies screaming to stick them on their trailers. It wouldn’t have taken long to figure out how to get it off and on, or design something else that worked the same.
    Curious this is being looked at now, when the push is on to save the planet.

  83. Anybody actually own a boat that has one of those boat tails ? Just curious.

    If the gizmo cuts the drag; it stands to reason that it would diminish the effect of drafting, which is dependent on driving in air that is moving forward.

    The 3-M sharkskin tape that Dennis Connor used on Stars and Stripes in the 1987 Americas Cup match in Fremantle Autralia; only works in water; it wouldn’t work in air. You can now buy fly lines (from 3-M Scientific Anglers) that have that sharkskin finish. They shed water like a greased duck’s back.

    There might be other surface finishes which reduce viscous drag in air. I notice that modern fighter aircraft have a dull matte finish on their pain jobs. Part of it is stealth (377 Ohm paint); but part of it is viscous drag; but maybe it is only effective at high airspeeds; so wouldn’t work on trucks.

  84. Those boattails just aren’t going to work. Since a trailer is length, width and height limited, it’s volume limited. Adding volume to the trailer to save fuel is less cost effective in the long run than adding volume to carry freight. Freight pays the bills. It may work on short trailers where GCWR is maxed out, like beer trucks. Mmmm, beer…

  85. Roger Carr (02:17:59) and LarryOldtimer (23:44:10), thanks for the reference on US fossil fuel reserves. It would be (and to some extent already is) the height of folly not to use our abundant resources for fear of CO2 and other eco-boogeymen.

  86. George E. Smith (10:52:21)

    The sharkskin does work in air, George. Airbus did some years a few years ago and got a 1to 2% drag reduction on a jet airliner. The biggest problem is determining the airflow direction to orient it properly. This works on powered aircraft in cruise as the aircraft flys over a narrow angle of attack range, not so well on gliders which need low drag over the whole speed range and the airflow can change direction significantly.

    Other problem was pressurization air leaks causing bubbles in the applique.

    I bought some of the 3M sharkskin in 1987. Never got around to installing it on anything and still got it.

  87. As commenters here have pointed out, all this truck drag reduction stuff dates back 35 years(first oil shock).

    Here we have universities and private industry paying to do the same stuff again. Is the human race losing its corporate memory?

    Is this an example of research being corrupted by governments making excessive amounts of money available for it?

    Do we have too many wannabe research scientists? Look at all the poor quality research being put out by the warmies.

  88. Glenn (10:32:45) :


    I may be wrong, but I suspect it makes the rear end squirrelly under certain conditions.

    That would make perfect sense, the experience of land speed racers with long tailed streamliners fits that expectation exactly.

    It would move the center of pressure to the rear when the trailer was hit by a cross wind gust, that would make the trailer tend to “wag its tail” in cross winds, If the frequency of gusts happened to match the natural oscillation cycle at a harmonic frequency, you could easily get the trailer swinging wildly from side to side in some cross wind conditions. It would also increase the “sail area” of the trailer to side winds, so both the side force would go up in high cross winds, but you increase the likelihood of the trailer blowing over if struck by a strong cross wind. That happens often enough as it is, when semitrucks are driving at right angles to gusty high winds. Here in Colorado during high wind events, they frequently have to close some highways to “high profile” vehicles to prevent blow over. About 20 years ago I watched a blow over occur right in front of me on I25 near Colorado Springs, just south of Monument hill in cross winds of only about 60 mph. The truck driver, was getting blown sideways, and gradually drifted to the edge of the pavement. Once he dropped the wheels off the pavement it was all over, and the vehicle rolled in the median, totally destroying the trailer.

    In a gusty cross wind quartering from the rear, it would likely rip the boat tail right off the trailer, as it pressurized that big cone, while creating a high pressure area on the up wind side, and a strong low pressure area on the down wind side.

    As a driver sharing the road I would not want to be anywhere near that thing in the type of high winds we sometimes have here in Colorado an Wyoming. I’ve had conventional trucks be blown almost a half a lane into my lane by a strong cross wind gust on several occasions.

    Larry

  89. Truckers are already trying to put 53 ft trailers into places designed for 45 ft ± trailers. Especially on the congested coasts the limit has been reached. Reduce the trailer length to 48 ft and then you might be able to run boat tails on a large scale, but the swing on sharp turns will still be hazardous in congested areas. Rookies will tear a lot of stuff up!

    As mentioned wind gusts will be catching these boat tails making the already high profile trailer less stable in crosswinds much easier to flop over anywhere or to skid loose on less than dry pavement. Having seen a person in a car crushed and killed, believe me, you do not wish to see it again. Very bad idea and fills me with dread.

  90. “”” Mike Borgelt (12:00:09) :

    George E. Smith (10:52:21)

    The sharkskin does work in air, George. Airbus did some years a few years ago and got a 1to 2% drag reduction on a jet airliner. The biggest problem is determining the airflow direction to orient it properly. This works on powered aircraft in cruise as the aircraft flys over a narrow angle of attack range, not so well on gliders which need low drag over the whole speed range and the airflow can change direction significantly. “””

    Well the original 3-M sharkskin tape that Dennis Connor used, has a preferred direction; the version they put on the fly lines does not; and it works as a result of the surface tension of water. In that sense it is less like true sharkskin. The flyline is even called sharkskin. It makes the surface hydophobicsince surface tension will not allow thw water to wet the surface at standard T&P, because of the short radius of the surface cavities.

    When you pick up the SS floating flyline from the water, it literally rains underneath the line. also as a result of the bumpiness of the line, it shoots through the guides like crazy; and in the process it makes a hell of a lot of audible noise.

    The 3-M tape is now illegal; at least for Americas Cup boats; but the sailors achieve similar results by sanding the surfaces with the right grit size sand papers.

  91. Morgan (07:00:44) :

    Hard to believe no one has brought up the recent Mythbusters episode in which golf ball-like dimples reduced a car’s fuel consumption by about 10%.

    http://access.aasd.k12.wi.us/wp/baslerdale/2009/10/24/mythbusters-golf-ball-car-better-gas-mileage

    I wish they had had that episode a couple weeks earlier. I could have gone to a junkyard and got a set of body panels for my Saturn (they come off real easily) and put dimples in them and then put them on on my way back from Oklahoma yesterday. That would have been a good 500 mile test. 500 down normal, 500 back dimpled.

  92. The nature of aerodynamics like this has been known for a long time, as many posters have pointed out. So why is this suddenly in the news now?

    In the UK with trucks of all sizes limited to 56mph in line with EU policy once they get onto the main roads (at least the ones that are not congested and are relatively free moving) they are often so close to each other they must pretty much be using the each other as Aero aids anyway. Sometimes in parallel rows, one truck taking miles to pass another.

    A few years back just after the law changed to allow bigger trailers but also the introduction of speed restrictors a trucker told me that at long last he was in a truck that was fuel efficient and had plenty of reserve power – until he came to a slope. At that point he would normally have built a little speed before the slope so that he could keep the engine at its optimum power output for most of the run up the hill. But being speed restricted he now had to go down through the gearbox. He reckoned it cost about 30% fuel economy in those situations – and there are many of those situations for UK truckers.

    Quite frankly there are greater benefits with no other issues against them to be had from looking at fuel efficiency in engines (which is of course happening) and improving the infrastructure (which if course for roads, in the UK and most of the EU is not).

    Meanwhile our local sub-government (under the EU) in London talks of spending untold billions to add another high speed (i.e. Passenger) rail link to connect the UK’s largest cities (London, Birmingham, Manchester and Glasgow/Edinburgh) apparently to encourage fewer people to fly between those places. It seems to me that with rail ticket priced the way they are they majority of people using the service are probably politicians, academics (on funded trips to other places of learning) and perhaps ‘entertainers/celebrities’. Ok there are a number of business people as well but on those very rare occasions when I use the train to go to London (no point in driving there) the perpetual conversations suggest that most of the business people, unless commuting to work as a daily ritual, maybe don’t really need to be making the trip.

    So if they stuff all the money for the next 20 years into a single rail link on a route that is already available today the chances that the rest of the infrastructure will fall apart are that much greater. Perhaps that is part of the plan. After all once the carbon taxes have made all forms of travel affordable only by the richest members of society who would need the infrastructure?

    It seems that that is where the money will go – a white elephant development that has little or no meaning for the lives of everyday people whose more direct infrastructure requirements will be ignored – at best. There is no benefit whatsoever adding aero aids to a truck that spend most of its time stuck at low speed in broken infrastructure.

  93. My understanding is that the US already moves a far greater proportion of it’s freight by railroad than does Europe.

    There has been lots of research into aerodynamics of cargo trucks. Basic issue: if you must reduce the cargo capacity to reduce the fuel economy, make sure that you reduce the latter more than the former, otherwise there is no net gain. And the resulting vehicle must be practical as well.

    My suspicion is that a lot of what is interpreted as “aggressive” or “fast” driving by trucks on US interstate highways is really an effort by the driver to keep as much momentum as possible in order to save energy and speed. I drove a 1000-mile trip in a 26′ truck, and drivers of cars thought nothing of dashing in front of me, slowing greatly, and then speeding up again. Meanwhile I’m trying to accelerate on an uphill grade and know that I won’t get above 45 MPH for another mile and a half because I’ve lost all of that energy.

  94. Yes this one of many designs produced over the years. The intention is to increase the the aerodynamic pressure at the rear of the vehicle and thus reduce the difference between the pressure at the front and rear. It can be very effective but is fraught with problems.

    This because of the danger of side [cross] wind buffet on the increased lateral area towards the rear which tends to cause the rear of vehicle to yaw or crab sideways at the rear.

    In a vehicle with a short rigid wheelbase this is quite desirable since by yawing the whole vehicle slightly into the direction of the side or cross wind it automatically counteracts any tendency to sideways drift.

    I believe the first car maker to successfully exploit this idea was Maserati in the 1970’s.

    But on an articulated, effectively hinged, wheelbase it is likely to cause serious difficulties in heavy side [cross] winds because although the tail moves laterally the front of the vehicle does not and this can only counteracted by the driver yawing the tractor unit with not necessarily predictable effects: depending on skill, loading, speed and force of the side [cross] wind etc.

    Moreover the rearward yaw or crab of the trailer unit alters the lateral air pressures on it, depending on the design, and this can aggravate the problem, if designed to be self compensating it can cause the tail to oscillate, swinging to and fro, and the action and subsequent degree of yaw can build up with surprising rapidity unless the driver counteracts it promptly.

    If it is not self compensating there is the risk that despite the driver trying to compensate it will steadily amplify the existing lateral drift until it becomes uncontrollable.

    Moreoever because of the problems of the position of the centre of gravity of the trailer, and thus loading, and its wheel placement, it is not possible to predict with any certainty how it might behave for any given set of conditions: only the driver’s experience and skill can cope with this.

    The only effective cures for this are automated dynamic ones which sense untoward lateral motion and correct for it. Aerodynamic attempts to do this have largely proved unsuccessful, whereas limited automatic rear wheel steering works very well. But although this was extensively researched and tested in the 1970’s/80’s I doubt it will ever be used on commercial articulated lorries.

    I suspect the simple answer is to unfold your wind cheating device in fine weather and fold it up when the wind blows. Bit like a friend of mine, a noted yachtsman, who keeps his spinnaker in the bottom of a chest of drawers and has no intention of ever getting it out even on fine sunny days.

    Kindest Regards

  95. Back in 1934 Ferdinand Porsche made a car with a special tail resembling a water drop cut 3/4 near the thin end. Many cars began using that design in the 70s, especially de 1976 Alfa Romeo Giulietta 1.8, with a high and short tail that later inspired almost all other European cars.

    See: http://imcdb.org/images/000/217.jpg

    The CX coefficient (drag) was extremely low, even much better than the Alfa GTV 2.0 coupé, that had the same concept of truncated drop of water “à la Prosche”.

    The secret seems to be in the turbulence created by the flat rear surface that replaces with advantage the missing part of the water drop.

  96. Gareth (05:09:58) : “Rather than the tacked on boat tail, couldn’t you just have the rear doors shaped like \/ rather than — ?”

    For aerodynamic efficiency, the taper angle has to be only a few degrees or so, as shown in the post. Using doors long enough to have a measurable effect on mileage would have all of the problems mentioned above: excessive length, added weight, added cost, and wind instability.

    Regarding weight: I recall a land speed record car crash of the late 50’s or early 60’s. The car had a lightweight tapered tail held on by what appeared to be 1″ by 1/8″ steel straps–more than adequate under straight-ahead full throttle loads. But the car began to spin out due to mechanical failure of another component. At the resulting angle, the wind force on the tail easily broke two of the straps. The open tail caught the air like a great big scoop and turned the spin-out into a horrific end-over-end fatal crash. [may have been the Athol Graham car; I’m not sure] You have to design any such tail for loads during a tail-wag. The required strength means a lot more weight, which would also accentuate a tail-wag by adding mass at the very end of the trailer.

  97. Ripper (22:48:53) :

    Here in Australia we have the worlds most efficient road transport.

    http://www.volvoadventures.com/164AusRoadTrain.jpg

    To get the endorsement to drive those wiggle wagons, you have to have a glass of water on your hood for a whole month and not spill!

    I don’t care how many baffles you put in there, I doubt you can come to a complete stop in that rig.

  98. @ D Johnson

    If you’re completely free to play with the tail shape of the trailer (like, say, a NACA 0012 airfoil) then you don’t have to have the flow detach and cause drag. You could get a perfectly laminar flow around the trailer with the two side flows merging at the end of the tail. Of course this only applies perfectly to airflow along the long axis of the trailer. Air coming from the sides, i.e. at a higher angle of attack, would cause sideways “lift” and in most causes detach from the “wing” of the trailer at some point. Just being pedantic. :)

    p.s. I don’t remember how to calculate the point of detachment either but I can still see the flow around a cylinder diagrams…

  99. All aircraft have the sme device (a pointy tail) – it is not rocket science.

    .

    BTW. Have you noticed that all those top-boxes people put on the roofs of their cars, are the wrong way around? Seriously, the pointy bit should be at the back, for maximum aerodynamic efficiency, not the front.

    Don’t believe me? Take a look at any airfraft wing. The leading edge (front) is quite blunt, but the trailing edge (back) is as sharp as possible. Why? Drag is caused by eddied at the rear of a body, rather than a blunt front – as this truck demonstrates.

    .

  100. I haven’t seen an explanation for this:

    How do you get ther truck into a dock.

    How much time and fuel does that take? Redeploying it?

    Is that included in the length limits?

    How many additional trucks does that require?

  101. Ron de Haan

    “CO2 is not a problem. It’s plant food. The greenest trees can be found next to the highway’s with the biggest traffic jams.”

    Firstly, we can only react in a responsible way to the research available to us. If what we are being told is substantiated, CO2 may well be good for the chlorophyl filled life on the planet, but obviously not so good for the ever-increasing greenhouse effect. If our planet was being populated by plants to neutralise our CO2 emissions, fair enough. Regrettably, our CO2 absorbing friends are being decimated. It takes one large tree a lifetime to absorb just over 1 tonne of CO2. One artic under normal circumstances will produce 80 times that in a one year.

    “… it will push the costs for distribution much higher than they are already without any sound scientific grounds.

    Even with the high fuel prices, distribution costs hardly play a role in consumer prices.

    The problem is with the independent truckers who drive the cargo based on fixed contracts. When fuel prices go up, they pay from their own pocket.”

    I find these comments quite staggering and a little short-sighted. As many in the UK industry will know, fuel is responsible for circa 1/3 to 1/2 of all transportation costs. If any aerodynamic addition reduces fuel consumption by even 2%, the net profit effect is very welcoming. The point is that cost cannot outweigh benefit. If a set of tail-fins costs £800 GBP and attributable fuel savings are £1,500 per annum, the ‘cost of distribution’ surely decreases. Your viewpoint represents a regrettably common attitude that focussed more on initial capital cost rather than operational throughout the lifespan of the vehicle.

    As for distribution costs not playing a role consumer prices, this is a very generic opinion that has little founding. It is true that independants on fixed contracts will not be able to pass on fuel increases, but these contracts are unviable. Many contracts in the UK are now linked with diesel prices.

    Any distribution company that is likely to survive the next decade would have already considered the fuel price increases (http://www.donbur.co.uk/gb/fueltrends.shtml) and made reasonable allowances for the term of any contract. As a result, it is reasonable to assume that consumer prices are indeed being driven up prematurely.

    Lastly, it is worth noting that overall distribution efficiency should be measured on a cost per stillage mile basis. On this basis, it is easy to determine that the most efficiency can be obtained in cubic capacity (The UK often utilise Double Deck 40′ trailers for trunking with 66% greater cube). Some comments here refer to the tapering of the rear to obtain a more aerodynamic profile, but eating into load space is counter-productive and leads to more deliveries and poorer overall fuel consumption.

    In comparsion to a single deck trailer, at say 9mpg, a double deck may only achieve 7mpg, but the cost per stillage mile is far better; a fact recognised by many operators, hence the call for larger, longer vehicles.

  102. Finally, as much as this boat-tail extends the overall length of the trailer past the trailer axles, turning sharply into a driveway from a main road will be a disaster for traffic in adjacent lanes. The swing of the boat-tail clearly, just by looking at the vehicle, would have to protrude into fast moving traffic creating a real hazard from both directions depending on the direction of the turn.

    Redesigning the doors, as previously mentioned, would also add expense as well as requiring more door seals. Door seals are an expensive item that are prone to leakage over time from wear and tear. They really leak when located along the sides of the trailer, as opposed to the rear.

  103. Speaking of railways, intermodal and container traffic is going to love what that does to their ton-per-car numbers.

  104. I’m not going to sieve through all the comments. A partial crawl finds no one who even comprehends 3-D geometry.

    The tests use an add-on – necessarily “hollow”. Boxes built with the boat-tail, of course, would not be. Loss of cube would be negligible – and when you’re loading out a box, you rarely fill the butt-end to the ceiling, anyway, unless you’re hauling light goods.

    American firms building similar – also offer mid-body skirts to grab some of the aero fuel economy inherent in possum-bellies.

  105. Richard Owens (01:28:59) :
    Al lot is done to make trucks aerodynamic efficient but costs and Government rules limit the possibilities.
    As stated, container transport is the biggest share of the transport market and there is nobody who will put a single dime in creating an aerodynamic container for the next twenty years.

    In regard to CO2, I am convinced it does not play an important role in our climate so every attempt to reduce it is superfluous and very costly.
    If we take away the uncertainties our carbon industry currently faces because of the political arm twisting and threats, there would be more product available resulting in lower prices.
    We can not survive in our modern cities without a well organized distribution system so my advice is to stop killing it.

  106. OK now lets think out side of the box for a minute. Why couldn’t trailers be tapered to the back end when built . in most cases they are unloaded one pallet at a time so if you tapered the trailer to the back and put the back door at the back of the taper then all will be happy and more efficient. Existing trailer cold be modified as well behind the rear wheels so long as you do not go past the 5′ restriction.
    Problem solved by an Australian.

  107. OK, let’s.

    How many dock doors will have to be rebuilt?

    Are there safety issues with fork-trucks ans stuff with that much weight behind the wheels when the load in the nose is gone?

    And so forth.

    How about we think the thing ALL the way through.

  108. Trucks are not the danger on our highways, uninformed and ill-trained car drivers are.
    The awfull truth is that everyday drivers have no idea of how different it is to drive a truck compared to a car. They assume the trucks act the same as cars, they don’t! They cannot stop on a dime or accelerate as fast as a car, but not many people seem to realize this.
    It’s time car drivers were better informed or trained!

  109. “The awfull truth is that everyday drivers have no idea of how different it is to drive a truck compared to a car.”

    The big problem here is that on the average, they have no idea how a car behaves, except on straight, dry, wade-laned pavement with a car immediately in front of them to tell them how fast to go and when to stop.

  110. This product along with the Portable Nose Cone Assembly from Hall-N-Binz, Inc. on intermodal containers would greatly stream line a train. Has any testing been done on a train load of containers with this product? What an interesting concept.

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