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Old 01-11-2013, 01:24 PM   #21
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That photo and question reminds me of an episode of Mythbusters. The myth they where challenging was if a pickup truck got better gas mileage with the tailgate down rather than up. The results came as a surprise to everyone.
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Old 01-11-2013, 01:55 PM   #22
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Yes Indeed but actually a more important question may be what configuration generates the most turbulence for the propeller? Propeller thrust may be decreased more than basic hull drag is increased.

I think perhaps the shape of keels like mine is descendant stuff from wood boats.

CP I saw that tailgate thing. I like mythbusting like my neighbor like "kill'in trees".
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Old 01-11-2013, 02:06 PM   #23
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Cars and trucks operate at a completely different speed from displacement boats, in hydro and aerodynamics tiny changes make a huge difference in drag.

But the trailing edge of the keel on a power boat is not tapered to reduce drag (though that is a minor benefit), it's to increase thrust. Getting clean undisturbed water to the prop is an important issue, a big fat keel in front of the prop blocks the flow, reducing thrust for the HP expended. The keel should be thick enough to house the shaft but tapered to 1" or less above and below the shaft line and the taper should extend forward a decent distance. Water doesn't like sharp corners, gentle bends are better......
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Old 01-11-2013, 02:08 PM   #24
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Quote:
Originally Posted by manyboats View Post

CP I saw that tailgate thing. I like mythbusting like my neighbor like "kill'in trees".
WHEW! Went right over my head but then I'm only 5'2".
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Old 01-11-2013, 05:59 PM   #25
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Sorry Walt.

Wer'e talk'in about the trailing edge of the keel right in front of the prop. The Mythbusting thing was/is a TV show about myths and old wives tales on TV.

TAD Thanks. One Willard owner reshaped his keel TE but he hasn't claimed his engine is now too big. Have you ever seen the keel TE of an early 60s Sumnercraft? Built in Amytiville NY.
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Old 01-11-2013, 06:54 PM   #26
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Tad, Eric the reference to the TV show was at one point they hydro tested the myth in a fish aquarium with a very gentle current induced. The way the fluid reacted to the obstructions in the water was quite fascinating and telling.

I did not mean to infer that boats and pick ups where analogous items. Only that the video segment showing the hydro test may help shed light on Eric's question of how the water reacts going around sharp edged surface.

As I can not find the video clip online it is a moot point now.
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