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Old 06-03-2008, 10:40 PM   #1 (permalink)
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Aero observation (kayak out the hatchback)

Last night I threw my kayak in my hatchback Aveo to do a little fishing when I got off this morning in a lake at work. The kayak will not completely fit in the car, about 2 feet stick out the back and the hatch is bungeed down and about half way open giving a longer sloping profile. There is a flat 12 mile stretch where I typically get 44-45 mpg on the scangauge. Last night with the kayak tail and the hatch sticking out into the slip stream it read 48-49 with an occational 50. I've got to check this out further. Maybe I have inadvertently created a boattail mod. It would be shame if I had to carry the kayak everyday to improve mpg, the fish dinner would be an added bounus. Oh, and I got 10 nice bluegill and 14" crappie and had a bald eagle buzz me. I must have invaded his fishing hole.

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Old 06-03-2008, 10:47 PM   #2 (permalink)
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Could the wind be helping you out last night? If not That would be an easy mod.
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Old 06-03-2008, 11:57 PM   #3 (permalink)
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would this be called a kayak tail then...
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Old 06-04-2008, 12:45 PM   #4 (permalink)
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"kayak tail" - too funny.

I think it's entirely possible that the angle of the hatch may have helped.

I've wondered this about my car as well, but the design of my hatch is such that opening it at all increases frontal area because of the hinge location and the design of the top of the hatch.

How about a photo?
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Old 06-04-2008, 04:10 PM   #5 (permalink)
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Kamm-Hatch?

Like Darin was saying,if the top didn't create a snag,and the slope of the hatch,say,didn't exceed around 15-degrees,it's not impossible that you created kind of a fastback.And with the gentle angle you would not have induced vortices at the sides.The space between the body and hatch/kayak would be the equivalent of the captured "phantom-boat-tail" Morelli,Kamm,and Korff,etc. elude to.Way fun! If I had a wider/shorter boat to loan you,I'd say,take it on your next outing and see what that would do.Great story,thanks.
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Old 06-04-2008, 07:39 PM   #6 (permalink)
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Here are some photos. I took it fishing again today and had high mpg on the scangauge. I going to keep it in the car till the end of the tank and see if there is a noted improvement. The wind was not a factor either time.
Attached Thumbnails
Click image for larger version

Name:	boattail1.JPG
Views:	129
Size:	33.3 KB
ID:	854   Click image for larger version

Name:	boattail2.JPG
Views:	116
Size:	34.4 KB
ID:	855  
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Old 06-04-2008, 08:50 PM   #7 (permalink)
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My yaks go on the roof, big drag mod. Scott
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Old 06-05-2008, 08:39 AM   #8 (permalink)
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It does look like it increases frontal area when open, but maybe the angles aft that are good enough to compensate for the increase.
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Old 06-05-2008, 01:46 PM   #9 (permalink)
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I think the only thing the kayak is doing to help is prop the hatch open. I'd experiment with a piece of wood propping the hatch open the same angle to see if the results are the same. Then make adjustments to the angle to find the optimum. After that I'd look to fill the gap with coroplast. VOILA! Instant boattail!
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Old 07-03-2008, 03:22 PM   #10 (permalink)
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Quote:
Originally Posted by homeworkhome53 View Post
I going to keep it in the car till the end of the tank and see if there is a noted improvement.
Any news on that front?

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