Better gas milage with boat cover on ?

[Water Dog]

Do any of you trailer boaters have any opinions on less drag / better milage when towing with the boat cover on or off ?
It seems I get better milage with the traveling cover on .
I KNOW I get better milage pulling with the van instead of the pickup even though they have the same motor / trans / rear gear ratios .
When towing with the van the boat cover has narry a ripple . The pickup however , creates big dents in the cover while towing .
Any opinions or towing storys welcome .

[perchjerker]

For what its worth. I read somewhere if you drive around in a empty pickup with the tailgate up, you add something like 400 lbs from the drag.

[Mike(Co)]

I checked it last week, between 1-2 mpg better with tarp on. No topper on truck right now. I will check it again sometime with topper. When I have the pop-up camper on it may not make much differance depending on the wind.
Good fishing
Mike

[Phil T.]

The only quantified measurements of your question I know of were done by GM a number of years ago. Yes, you will get better mileage with a cover on your boat. An open boat tows like a covered one that's 2' longer, and that much heavier.
As for the pickup, the best mileage will be achieved with the minimum air turbulence in the bed behind the cab. Sorry to burst everyone's bubble, but GM, Ford, and Mopar all agree that the best aerodynamics are with a covered bed, second with the tailgate in, worst without a tailgate or with one of those louvered tailgates that the 5th wheelers use. What seems obviously logical isn't necessarily true when real data is collected.
It all has to do with the amount of air that swirls around in the open boat or in the open pickup bed.

[Skeeter]

Perchjerker, believe it our not there is a guy on this site that wrote sometime back that with the tailgate up you will get better mileage. He works at a place that studies aerononics, and specializes in that area and proved because of the way the air goes around and down and whatever that best mileage is received with tailgate up. I know it doesn't stand to reason but thats how some things work I guess.

[SUPERTROLLER]

I read a study on this somewhere too. It stated that the ventilated tailgates and cargo nets placed on the back of truck boxes actually increased drag coefficients. The theory is that when the tailgate is up the air trapped in the box actually acts like a tonneau cover. This keeps the air coming over the top of the truck cab out of the box and makes the truck more wing-like, thus the lower drag. Makes some sense but it's hard to believe that the tailgate isn't like a parachute collecting air back there.

[Chevy4sur]

Phil T...What you say makes sense to me and is supported by the data. Thanks. Jack.

[Ristorapper]

I put a glass-tite topper on my p-up and have since never put the cover on my boat except in the chance of rain. I have the tall topper that goes above the cab of the truck and the few times I did tarp the boat after I mounted the topper on the truck, the tarp had very little movement; therefore I seldom tarp the boat now.

BW(ND)