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Air drag while towing an open boat

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  • Air drag while towing an open boat

    I was wondering if adding a cover on a boat would make a big difference on the air drag while towing a boat.

    The objective is to reduce the fuel conssumption while towing on long distance.

    I measured the difference between towing my utility trailer "loaded" and towing my boat and the difference is substential.

    The boat with the trailer is 350# and I average 20mpg and the utility trailer at 800# will average around 29 mpg at the same speed.

    So it's a question of air drag that reduce the performance.

    I know some pickup remove the tail gate or add a cover for the bed to have less air drag, so will adding a cover on boat have a substential improvment in air drag performance?

    Thank you.

  • #2
    Re: Air drag while towing an open boat

    I would think so. Give it a try. It will keep the bugs out of the boat at least.
    2013 Bayliner 255CR
    5.0MPI S/N:2A044802
    http://seawenchnc.blogspot.com

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    • #3
      Re: Air drag while towing an open boat

      A towing cover, tight and smooth, will improve mileage. In my ML, towing a BW Montauk, the difference was 18mpg vs. 15mpg.
      sigpic

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      • #4
        Re: Air drag while towing an open boat

        I've have poor luck with any so-called "trailerable" boat cover. They all seems to blow up like a balloon no matter how well I have them fastened down. I think the only true trailerable cover is a custom made one (and you can buy a LOT of gas for the price of one of those).
        2002 20' Hydra-Sports 202DC 200HP Yamaha HPDI
        1976 18' Starcraft SuperSport 90HP Evinrude
        Restoration thread https://forums.iboats.com/showthread.php?t=357767

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        • #5
          Re: Air drag while towing an open boat

          Originally posted by shingo View Post

          The boat with the trailer is 350# and I average 20mpg and the utility trailer at 800# will average around 29 mpg at the same speed.

          Thank you.
          What are you using to tow to get those numbers is what i would like to know.800 lbs 29mpg vs 350 lbs 20mpg? I can't even get that with any vehicle i have.(avg)
          Assault Squadron NINE
          River Assault Division NINETY-ONE-1966

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          • #6
            Re: Air drag while towing an open boat

            Originally posted by Thalasso View Post
            What are you using to tow to get those numbers is what i would like to know.800 lbs 29mpg vs 350 lbs 20mpg? I can't even get that with any vehicle i have.(avg)
            It's a VW Golf GTI stage 2, it's a 2.0 liter turbo, mine is making 300hp@4000 RPM and 350 torque@2500RPM.

            The car is rated to tow 1850# if the trailer do not have a braking system and 3500# if the trailer has a braking system. It's the official manufacturer limit on towing capacity.

            It's a 6 speed DSG transmission and Direct injection engine.

            It's the power of the turbo, I got enough boost to accelerate without any problem and when I'm at the cruising speed on the highway the turbo are not in use and it's very efficient. The problem is that if the trailer has too much drag or is too heavy then they turbo will have to work a lot and the fuel efficiency is a lot worst.

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            • #7
              Re: Air drag while towing an open boat

              Originally posted by shingo View Post
              I know some pickup remove the tail gate or add a cover for the bed to have less air drag, so will adding a cover on boat have a substential improvment in air drag performance?

              The car is rated to tow 1850# if the trailer do not have a braking system and 3500# if the trailer has a braking system. It's the official manufacturer limit on towing capacity.
              Dropping the tailgate actually hurts mileage, and the bed covers have little to no impact either way. In an empty pickup box, you get a nice rolling bubble of air that works to deflect the air moving over. it basically forms a nice aerodynamic cover.

              Anyway, if you have a GOOD 100% custom fit cover, it will certainly help. A universal or semi-custom cover could very likely hurt mileage. You need something that fits like a glove and doesn't billow up in any spot. I personally notice a big difference towing my boat (2000# or so) with my turbo wrx. (although I don't get mileage anywhere close to you, towing at 75 mph with the boat behind puts me about 13 mpg, gasoline though)

              also, you are outside the US, so you are safe from our sue-happy environment, but even so, that tow rating is on the VERY optimistic side. A 3500# load behind that, with sufficient tongue weight, will most likely bend up the unibody if you have to actually stop in a hurry. Lastly, you won't be able to find a class 2 or 3 hitch for that. Class 1 is limited to 2000 pounds/200 pounds tongue weight max.

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              • #8
                Re: Air drag while towing an open boat

                Originally posted by Thalasso View Post
                What are you using to tow to get those numbers is what i would like to know.800 lbs 29mpg vs 350 lbs 20mpg? I can't even get that with any vehicle i have.(avg)
                Canadian Gallons are 20% Larger than US gallons.

                But we will assume he took that into account during the KPG to MPG conversion.
                Bill, Lorain Ohio

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                • #9
                  Re: Air drag while towing an open boat

                  It's us MPG, I did the conversion from l/100km to mpg

                  it's 8.5L/100km with the 500# trailer.

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                  • #10
                    Re: Air drag while towing an open boat

                    Your right, shingo, doesn't look right.

                    Maybe check your bearings, tires, suspension on the boat trailer?
                    BOAT=Best Of All Times

                    "Everyday above ground is a good day"

                    Winterization=sneekers, jeans and a sweater.

                    Same Ship.....Different Day.

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                    • #11
                      Re: Air drag while towing an open boat

                      i get 9mpg towing without the cover and 12 with it. 19ft bow rider with cockpit cover and bow cover. 3700 lbs boat/trailer weight. i get 16 mpg without towing.
                      Ryan

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                      • #12
                        Re: Air drag while towing an open boat

                        Towing my 21' deckboat long distance at highway speed, mpg is 20% better with cover on. Without question.

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                        • #13
                          Re: Air drag while towing an open boat

                          I get 10 mpg towing my 12ft boat. and 10 mpg without it, i need a new truck....

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                          • #14
                            Re: Air drag while towing an open boat

                            Originally posted by shingo View Post
                            It's us MPG, I did the conversion from l/100km to mpg

                            it's 8.5L/100km with the 500# trailer.
                            I would have guessed that km/L or km/gal(4L) would have been the norm.
                            I am surprised at the L/100km unit where a lower number is better.
                            It is always interesting to learn what folks in other countries use as standards.

                            8.5L/100km = 27.7mpg by my conversion.
                            I don't see that number in your posts.
                            I also couldn't find a 500# trailer either.

                            The boat with the trailer is 350# and I average 20mpg and the utility trailer at 800# will average around 29 mpg at the same speed.
                            Did you really mean a 3500# boat and trailer?

                            -----

                            In any event the boat will likely be much more aerodynamic than a utility trailer with a flat front end.
                            The weight of the trailer makes a difference starting and stopping, but not at a constant speed.
                            The air drag is the overwhelming factor once you are at cruise speed.

                            Unless you already have the cover or were going to buy it for another reason;
                            You will likely wear out the cover before you you could pull it enough miles to recover the multi-hundred dollars it will cost.
                            Bill, Lorain Ohio

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                            • #15
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                              Re: Air drag while towing an open boat

                              I tow a 14' jon boat with our Honda Accord, without the cover about 18MPG, with the cover about 22MPG (without boat 27-28MPG). Using the cover helps mileage, but I don't use it unless towing over 100 miles, it's a pain messing with the cover 4 times during a trip....on-off-on-off.....

                              EZ is right about getting a tight fitting cover, I sewed in a bunch of tie-downs to my cover to keep it taught, then bungee cord around the outboard. If the cover flaps around while towing, it will rip itself apart.
                              2001 Crestliner SuperHawk 1800, Mercruiser 140HP
                              2007 Tracker 1436 jon boat, 7.5HP Force

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