Boat tail mod to my enclosed trailer

[max_frontal_area]

Originally Posted by Braebyrn

15.66 mpg, at 60 mph. on flat and level.

hot dam! it is so nice to see somebody doing instead of just talking.
continuing those ridges until they converged like4 the study you cited would have likely done more for you since it doesnt look like you have any kamm effect going on there. are you planning a cone for the front as well?

what is your tow vehicle, does it have a wing on it or a cap or ...?
what is the total loaded weight?
acellerating rigs like this from a dead stop is what really soaks.
i carefully listen to the engine, if it has a torque converter. your truck will only acellerate so fast any extra pedal and your fuel will flush out the back!

[KamperBob]

Keep up the great work!

I wouldn't expect any difference whether the back is open or closed in your case. The angles are closing pretty quickly by that point. I wonder where flow detaches. Before there I suspect. Tufts would help if possible.

Your data so far shows considerable variation tank to tank. Still, the response to mods seems clearly positive. :thumb

Cheers
KB

[Braebyrn]

Originally Posted by max_frontal_area

hot dam! it is so nice to see somebody doing instead of just talking.
continuing those ridges until they converged like4 the study you cited would have likely done more for you since it doesnt look like you have any kamm effect going on there. are you planning a cone for the front as well?

what is your tow vehicle, does it have a wing on it or a cap or ...?
what is the total loaded weight?
acellerating rigs like this from a dead stop is what really soaks.
i carefully listen to the engine, if it has a torque converter. your truck will only acellerate so fast any extra pedal and your fuel will flush out the back!

I had a nose cone on there last week. Trying to get the data from one to the other. I wish I had it in the trailer, I would have put it on, but its at home.
My tow vehicle is a 2003 GMC with a 2006 Duramax LBZ diesel motor. It has a cap that has a slight angle up. I will have to go over the scales to let you know the weight on the setup. I am so trying to get the best fuel mileage out of this that I drive the people behind me nuts, I'm sure. I don't idle the truck unless I have to, etc.
I just unhooked the trailer and am driving without the trailer and am back up to 21mpg aprox. I have about 1000 miles before I put the trailer back on. Its the best fuel mileage that this motor has gotten. The air dam, side skirts and the bumper opening mods really are helping.

[Braebyrn]

Originally Posted by KamperBob

Keep up the great work!

I wouldn't expect any difference whether the back is open or closed in your case. The angles are closing pretty quickly by that point. I wonder where flow detaches. Before there I suspect. Tufts would help if possible.

Your data so far shows considerable variation tank to tank. Still, the response to mods seems clearly positive. :thumb

Cheers
KB

KB,
I really don't understand the differences from tank to tank either. I know I am not on a oval track, so it must be wind, hills, construction, etc. I am only stopping for fuel and excercising at the rest stops. No stop and go traffic, just set the cruise and go. Roads are clear and haven't had any traffic to speak of.

Taking the square opening off didn't seem to make any difference on the next two tanks, although I seem to get more lookie looos with it off.

[max_frontal_area]

Originally Posted by Braebyrn

just set the cruise and go.

DON'T! cruise control monitors vehicle speed many times a second and adjusts it accordingliny by adding more fuel or less as needed or even decellerating via brakes, which can be a big deal in a heavy setup like yours.

i wedge my right foor between the gas pedal and transmission tunnel.
it will aslo help to be proactive and watch for hills and speed up accordingly
to build momentum, just watch for the fuzz! on the downhills get off the gas once you have reached the top, properly timed you will save a bit of gas until you have to brake... proper driving techniques can save a lot of juice on a rig your size.

[KamperBob]

MFA was spot on.

I only use cruise control strategically. As long as the TC stays locked then cruise is fine and does not hurt MPG. When the transmission tries to "help" maintain speed, all bets are off.

Learning my shift points was key. In D my min lockup speed is 40 mph on accel and 35 on decel. In OD it's 45 accel and 40 decel. OD is my truck's default mode, and my power to load ratio is high enough that most of the time I can tow in OD. When inclines are too much for OD then I adapt first by gaming the hills like a trucker, and manually select D mode if needed. On a typical 1100 mile trip between MA and IL there are only a few miles of grade in PA where D is needed for my rig (power/load). In a rig with more weight and drag I might spend more miles in D than OD.

Goal #1 for me is minimizing transmission temp. That means not letting the TC unlock. Stirring ATF generates heat. Heat kills trannies. Meanwhile, torque converters hurt MPG.

On long down grades I used to think coasting was best for MPG. One thing my ScanGauge taught me, however, was that engine braking is often better. Instead of idling at 0.5 gph my injectors get shut off so zero fuel gets burned. My trans fluid is usually warmer going down than up as a result. Doesn't seem intuitive, and may not work well for others but works for me.

Another trick I learned was that flashers are my friend. They ward off tailgaters like deet on skeeters!

Cheers
KB

[JasonG]

How heavy would you estimate it to be ?
I was looking at "Waggoneer" car trailers today. They have a rear hatch similar to yours but they rounded it way to steeply to do much good.
It hinges at the top. I was thinking it would make a nice awning for the ramp when i was parked.
What size hinges did you use and how many?

[Braebyrn]

Originally Posted by max_frontal_area

DON'T! cruise control monitors vehicle speed many times a second and adjusts it accordingliny by adding more fuel or less as needed or even decellerating via brakes, which can be a big deal in a heavy setup like yours.

i wedge my right foor between the gas pedal and transmission tunnel.
it will aslo help to be proactive and watch for hills and speed up accordingly
to build momentum, just watch for the fuzz! on the downhills get off the gas once you have reached the top, properly timed you will save a bit of gas until you have to brake... proper driving techniques can save a lot of juice on a rig your size.

I tried to not use the cruise control and seem to have my right foot fall asleep! Must need more exercise.... I will give it a try and see what happens. Thanks

[Braebyrn]

Originally Posted by KamperBob

MFA was spot on.

I only use cruise control strategically. As long as the TC stays locked then cruise is fine and does not hurt MPG. When the transmission tries to "help" maintain speed, all bets are off.

Learning my shift points was key. In D my min lockup speed is 40 mph on accel and 35 on decel. In OD it's 45 accel and 40 decel. OD is my truck's default mode, and my power to load ratio is high enough that most of the time I can tow in OD. When inclines are too much for OD then I adapt first by gaming the hills like a trucker, and manually select D mode if needed. On a typical 1100 mile trip between MA and IL there are only a few miles of grade in PA where D is needed for my rig (power/load). In a rig with more weight and drag I might spend more miles in D than OD.

Goal #1 for me is minimizing transmission temp. That means not letting the TC unlock. Stirring ATF generates heat. Heat kills trannies. Meanwhile, torque converters hurt MPG.

On long down grades I used to think coasting was best for MPG. One thing my ScanGauge taught me, however, was that engine braking is often better. Instead of idling at 0.5 gph my injectors get shut off so zero fuel gets burned. My trans fluid is usually warmer going down than up as a result. Doesn't seem intuitive, and may not work well for others but works for me.

Another trick I learned was that flashers are my friend. They ward off tailgaters like deet on skeeters!

Cheers
KB

I have the six speed auto tranny and I never see the torque convertor unlocked on the CTS monitor. I will look closer at that today.

I did however notice that the best fuel mileage was when the fuel temperature was around 93. After the outside temperature warmed up and the fuel temp went up to around 120, the fuel mileage began to drop. The airdam and side skirts are surely not helping to keep the fuel temp low

As for the engine braking, I love that feature on the truck. Hit the tow/haul switch on the shift selector and that really helps in going down hills. I just didn't know that they shut off the injectors. Thanks KB.

[Braebyrn]

Originally Posted by JasonG

How heavy would you estimate it to be ?
I was looking at "Waggoneer" car trailers today. They have a rear hatch similar to yours but they rounded it way to steeply to do much good.
It hinges at the top. I was thinking it would make a nice awning for the ramp when i was parked.
What size hinges did you use and how many?

Truck 7000, trailer 3500, car inside 4000. The boat tail mod that I made from scrap pvc pipe and coroplast hinged at the top. I had to prop it up and was not fun near the ocean when the wind came along. But your right, extra cover from the weather.

If you used some of those hood prop cyclinders or the cap ones, that would be good. Just would hate to drop it on the car.

I had to put the hinges on the side since the roof on the trailer is curved and making a hinge work there was a bit of a challange. The hinges are cigar shaped and about the size if a magic marker. There is three of them welded to the trailer.