I have a 2009 2500HD 6.6 duramax on my trip from Pensacola, Fl to Key West i got about 6.5-8.3 mpg. I'm pulling a 31' CapeHorn boat w/ dual axles, surge brakes in tow/haul. running about 70 mph. The boat weighs about 5000#, twin engines 1050#, trailer 2700#, about 50gal of gas in tanks so thats about 400-500#. gear in truck & boat about 1000# +/-, and 4 people.
Truck is factory stock with no mods. Besides a small fuel tank .(26 gal) Which I don't like. Does this sound normal to you? I would've thought it would be at least 10-12mpg. Any suggestions before my next trip.

Thanks,
Mike

I assume it is a hard top. I tow two different boats from MD to the Keys and after only about 9.5 at 70. There is something about the shape of a boat on the trailer that it just sucks from an aerodynamic standpoint. The only thing that seems to help is to keep the speed down to 65 and use the cruise as much as possible.

paper, my 05 gets 11-13 towing the same weight in travel trailers... use the cruise as much as possible.. im in cantonment, welcome to dp..

:welcome: to Diesel Place!

Your choice of speed is what is trashing your towing MPG. Drop to 60 MPH and you will probably see that 10-12 MPG you were expecting and it only costs you an extra 10 minutes for every hour you drive - not a big deal in the grand sceme of things.

I tow a 12,000 Fiver with a much more dramatic aerodynamic profile than most boats and get 10.5 MPG towing with much less of a truck then you have but without exception I always tow at 60 MPH.

Also take note, most trailer tires are only rated for 65 MPH to begin with. 70 MPH isn't a big stretch, but it is still technically exceeding their speed ratings.

Nice boat.

As mentioned, depending on the angle of the hard top during tow, I could see it acting like a parachute behind you. Unlike a TT or enclosed hauler, you are not just pushing into the air, there are vortexes that are created by the cockpit etc that literally suck.
If you have a tight fitting, snap around mooring cover you might try that but I dont know how well that works with a center console. I did notice a slight difference with my cuddy.
The upward sloping bow that lets you crush the chop may also be working against you.

I get about 12.5mpg @68 towing my 7k gross MasterCraft with tower, speakers are removed + 1k in bed

Slow down to even 65 and you will gain 1-2mpg. If you are not willing to slow down, you are pretty much trading time for money. Find a point you are comfortable and move on.
I have found towing in M5 to be more efficient than letting the trans go to 6th if you are under 75mph.
Of course take winds into consideration with mpg expectations. I have hit 30mph constant head winds gusting to 40+ that dropped me to 9.

Also, you dont specify but hand calc is the only true tale. People can argue all day long but never trust the DIC values (they are usually higher)

Enjoy the truck and know a gasser would be getting even less :)

Unfortunately, that sounds about right. A lot of people underestimate the aero drag a large profile object creates. I mentioned this before...I get the same mileage pulling my race car trailer (fully laden around 14K pounds) as I do our two-horse straight load trailer (fully laden around 7K pounds). The difference is that the horse trailer is about 3 feet taller to accommodate our 18hh horse. That wind resistance is a killer on fuel mileage.

If you can, keep the speeds down to help with the mileage. In California, I have to keep it around 60 mph (55 mph speed limit while towing), so mileage towing my trailers is around 13-14 mpg. When I tow out of state and do around 65-70 mph, my mileage plummets to around 9-10 mpg.

really? is that just because of the LMM? I got 10MPG pulling a 44' GN that weighed 17K at about 75mph.

6.5-8.3 seems really low

As mentioned above, aerodynamic drag is likely the biggest challenge you have.
On a six speed are you letting it into 6th (double overdrive)?
I am not sure what the sweet spot is for your engine RPM, but maybe you should try running if 5th. Let the RPM run up a bit and not lug. '05s and older have no choice and that engine has legs at 2200 RPM.

really? is that just because of the LMM? I got 10MPG pulling a 44' GN that weighed 17K at about 75mph.

6.5-8.3 seems really low


that's what I was thinking, but who knows.

I just went from Chicago to Moab and back. I was between 9-10 mpg even through the huge passes around Denver and Vail. my total weight is somewhere around 22,500# and not the most aerodynamic setup either (or maybe it's better than I think)

32' GN
http://www.houseofloy.net/smsmith/Moab_2010/MoabUT2010_Steves/dscf0241.jpg

1tfrot,

That is a lot more aerodynamic than a boat. First boats tend to sit high on the trailer creating a lot of wind going under the boat. Second, you would be amazed at how wind swirls inside. You will find bug splatter on every surface inside, even facing forward and the sides.

I average 10.5-12.0 with my toy hauler. It's 15K gross weight loaded. The last trip I had a 25+ mph head wind and dropped into the 8's.

1tfrot,

That is a lot more aerodynamic than a boat. First boats tend to sit high on the trailer creating a lot of wind going under the boat. Second, you would be amazed at how wind swirls inside. You will find bug splatter on every surface inside, even facing forward and the sides.


that's cool, can't argue that. never owned a boat ;) does make sense though

that's cool, can't argue that. never owned a boat ;) does make sense though

Yep, your set up is not too bad, all things considered. The tough thing with boats, as diesail mentioned, is often the height/profile, and combined with all of that surface area, they can be a drain on mileage despite not weighing nearly as much as some of the travel or equipment trailers.

Agreed with the others.
I tow a 23' open bow that weighs ~ 6500# total loaded with trailer; and I also tow a ~ 2000# popup trailer behind the boat at times.
I have a travel cover for it, but i have towed it on a couple of day trips without the travel cover ~ 160 miles round trip. I was very surprised to see LOWER mileage towing ONLY the boat without the 2000# pop-up.
On one day trip without the cover on the boat I got 10.3 MPG. (I average 11-12 MPG towing the triple setup). The biggest problem towing only the boat is I tend to cruise at 75 MPH.
When I tow the triple setup I cruise at 65 MPH and never above 70.

I its possible to put a travel cover on your boat, it will help.
Slowing down while towing will help more.

Agreed with the others.
I tow a 23' open bow that weighs ~ 6500# total loaded with trailer; and I also tow a ~ 2000# popup trailer behind the boat at times.
I have a travel cover for it, but i have towed it on a couple of day trips without the travel cover ~ 160 miles round trip. I was very surprised to see LOWER mileage towing ONLY the boat without the 2000# pop-up.
On one day trip without the cover on the boat I got 10.3 MPG. (I average 11-12 MPG towing the triple setup). The biggest problem towing only the boat is I tend to cruise at 75 MPH.
When I tow the triple setup I cruise at 65 MPH and never above 70.

I its possible to put a travel cover on your boat, it will help.
Slowing down while towing will help more.

Is this even legal?

Is this even legal?

Depends on where you live, but doubles (which is actually what double trailers is referred to, not triples as suggested) is legal if your State/Province allows it, and you have the required licence, certifications, or endorsements, if required.

When we travel long distances I pull a second trailer behind my fiver - we put our 4 bikes on it, our aux water tank (we boon dock a lot and it carries an extra 250L of water) and any other gear we don't have room for elsewhere. Last summer I used it to bring our smokers to a campsite for a rib-fest. ;)

Here's a pic:

http://gallery.me.com/oshawapilot/100049/DSCF9005.jpg?derivative=medium&source=web.jpg&type=medium&ver=12940139320001

Yes. I live in Alberta, Canada where this IS legal, but ONLY behind a 5th wheel. The poster is talking about towing a pop up behind a boat. Don't think THAT is legal ANYWHERE.

Yes. I live in Alberta, Canada where this IS legal, but ONLY behind a 5th wheel. The poster is talking about towing a pop up behind a boat. Don't think THAT is legal ANYWHERE.

It is in some US states. Here in Ontario it's also specified that a double combination must have a fifth-wheel (or Gooseneck) as the lead, but elsewhere dual ball-hitch combinations are legal.

In the early 90's I pulled such a setup - a 14' ball hitch camper with a 15' boat behind it. I was ignorant to the laws at that point and for all I know the fifth-wheel lead stipulation didn't even exist at that point..but it seemed stable in my small setup. I can totally understand the point behind the law though - make the first trailer a 30' ball hitch RV with a smal boat behind it (for example) and the RV would be whipping the boat all over the road.

Yes. I live in Alberta, Canada where this IS legal, but ONLY behind a 5th wheel. The poster is talking about towing a pop up behind a boat. Don't think THAT is legal ANYWHERE.

It is legal here in Utah. Not sure that is should be -- I've seen some questionable setups, to say the least -- but that's another discussion.

Go to The Hitch Store.com, then to there Towing Info link a lot of information to be found there for US and Canada.

Is this even legal?

Yep. It is in Utah at least.
There are various towing laws that must be met, overall length less than 65 feet, GCVW, etc.

I'm legal with the pop up behind the boat both as "bumper pull". My setup works fine, and I have had zero issues.
Like I said I keep the speed down towing the double, I also upgraded the brakes on my boat trailer to electrics for better control instead of the surge brakes it had before.

In the summers here you can see a double tow behind an HD truck pretty much daily. Lots of guy doing it.

Wish I could do it hear ont he east coast.

Yep. It is in Utah at least.
There are various towing laws that must be met, overall length less than 65 feet, GCVW, etc.

I also upgraded the brakes on my boat trailer to electrics for better control instead of the surge brakes it had before.


The electric brakes are key in your doubles. Pretty sure electric or air brakes on the first trailer is a legal "must have".

Laws are different state to state so check and double check for every state you would travel though.
Just because one state allows it, others do not have to reciprocate.

I was getting (towing a 8k+ trailer) 9mpg at 1st, then 15/16mpg later when I got great fuel in vegas.

DPF delete... truck can't breathe.
I know it's expensive but EFI live tow tune from someone like Nick, EGT and boost gauges, 3" downpipe, 4" aluminized muffled exhaust. I'd be willing to bet the first new experience towing would be 10x better than it used to be.

This was my latest pull, went from South Eastern KY a bit north of Indianapolis IN. I only figured the first tank. Haven't driven the truck since June so I kept forgetting to reset the trip or figure the mileage. But the first tank was 10 something MPG, going 75/80. Not sure of the weight, but my 96 is right around 5k so I figure probably around 7k truck and trailer. Did that drive last week. I have gotten up to 16 pulling my Camaro, but that was warmer weather (summer fuel) and driving about 65 mph. Less weight, lower car/less drag, and also the car is a bit more areo dynamic anyway.
Point of all this being, winter fuel, speed, hills (speaking of had some on the way up this last trip) will all kill mileage.
Also a couple things you can do to help. First drive with a light foot. (take off slow "doesn't have to be grandma slow, but easy"), keep your tires aired up, keep your brakes clean (draggin brakes less mileage), don't touch the brake (think of it this way, sitting at one stop light stomp on it, get to the next one quick and stomp on the brake. Using the brakes "absorbs/wastes" the engery/fuel you used to build your speed. Same thing, take off easy, coast almost to a stop tap the brake and stop. Less fuel used less brake to absorb that energy carrying you forward.) Hope that makes enought sense. If you start changing things on the body. A bed cover can help mileage, wider mirrors will create more drag, tires/mirrors that stick out more will cause more drag, and "holes" for air to find will create more drag, ect...
Biggest thing you can do without spending money, slow down.
http://i243.photobucket.com/albums/ff13/kcb37_2007/Doolittle/P1000160.jpg
http://i243.photobucket.com/albums/ff13/kcb37_2007/Duramax/DSCN1062.jpg

Like stated above.....delete that DPF and get a small tune or just a tune to delete the code after deleting the DPF.....I have a tow tune and intake and exhaust with EFI live and from 62 or 63 to 75 i get 11 mpg with a 27sea hunt with triple axle trailer, about same weight as yours actually.... where in ptown are you from? I went to escambia high out there. C/O 2000

Has anyone tried using a wind deflector, that either mounts to the top of the cab, or sits in the front holes of the truck bed. They should divert most of the wind up over what ever you are towing.

Like stated in numerous post a small tune and drive by the RPMs rater than speed and you will see major differences. I regularly tow a double car hauler and a 30' 5er (not together) and normally see mid teens.