Golf ball dimples on the hull bottom?

[ScarabChris]

Yeah that sounds crazy. But its a known fact that golf balls are dimpled for longer flight. Something about the dimples allows the air to slip over the ball easier.

I just watched Myth Busters. The myth was would a dirty car get better milage than a clean car because of the golf ball effect. Well the dirty car got worse milage.

But when they put dimples in the car resembling a golf ball the car went from 26 MPG to 29 MPG at 65 MPH.

How about dimples on the hull bottom to achieve the same effect? I have heard that some boat racers sand the shine off the bottom to help break the boat from the water.

Any thoughts?

[triumphrick]

Yeah that sounds crazy. But its a known fact that golf balls are dimpled for longer flight. Something about the dimples allows the air to slip over the ball easier.

I just watched Myth Busters. The myth was would a dirty car get better milage than a clean car because of the golf ball effect. Well the dirty car got worse milage.

But when they put dimples in the car resembling a golf ball the car went from 26 MPG to 29 MPG at 65 MPH.

How about dimples on the hull bottom to achieve the same effect? I have heard that some boat racers sand the shine off the bottom to help break the boat from the water.

Any thoughts?

Ball peen hammer??

Where's Mike Carrigan when we need him??

Edited October 22, 2009 by triumphrick

[ScarabChris]

On Mythbusters they actually put a layer of clay on the entire exterior of the car, 800 pounds of it! They had sculpters carve and shape it so it followed the original lines of the car, it looked perfect.

Then they did a test run with it nice and smooth. Then they put the dimples in it that were about as round as a soft ball. Then they tested it again......3 MPG more.

[yottyboy]

OK, so now Mythbusters is the go to authority on aero- and hydrodynamics? I think I'll trust people with actual degrees in the subject.

The problem is that water is far more "sticky" on a molecular level than air. It's also far more dense, and, well, it's just different as you can certainly tell. Therefore, it is false to assume the same things that work in air will work in water, even though they are both fluids.

[Cracker Larry]

Also, boat hulls are not round, not spinning and not flying 100 mph through the air. A lot of tests have been done with dimpling, both sailboats and power boats. In all cases it increases drag.

One reference http://www.hydeoutdoors.com/boats/randd/

excerpt,

Although in principle this would work for what fluid engineers refer to as a "bluff body", such as a cylinder or a golf ball, it shouldn't apply to a "streamlined section", such as a sailboat hull. Even if you consider the hull a bluff body (and I've seen some production hulls that come pretty close), the drag coefficient is only lowered within a certain range of velocities. For a golf ball in air (a small object in a fluid that isn't very viscous) the drag coefficient is lowered between about 20 m/s (meters/second) and 80 m/s (about 40 to 160 mph). For a Victory in normal salt water (a much larger object in a much more viscous fluid; of course, the water in GSL is even more viscous) the drag is only lowered between about 0.01 and 0.04 m/s (about 0.02 kts and 0.08 kts). More importantly, above 0.04 m/s dimpling will _increase_ the drag coefficient. At about 2 kts the drag coefficient will be about doubled. Of course, this is assuming that the hull is acting as a bluff body, which it really isn't. For a streamlined section roughness will _always_ increase the drag coefficient of the hull at all but the very slowest speeds (for a Victory, speeds below about 0.3 kts). Therefore, when dealing with boat hulls, its always prferable to have as smooth a surface as possible.

[ScarabChris]

OK, so now Mythbusters is the go to authority on aero- and hydrodynamics? I think I'll trust people with actual degrees in the subject.

The problem is that water is far more "sticky" on a molecular level than air. It's also far more dense, and, well, it's just different as you can certainly tell. Therefore, it is false to assume the same things that work in air will work in water, even though they are both fluids.

Sorry...I don't know where I said Mythbusters was the "go to authority on aero- and hydrodynamics" I just watched the show and was wondering if it were possible to get a similar effect in water.

Oh and uhhh...they did a scale test in water as well. They put a model of a car with and without dimples and the model with dimples had less resistance.

And uhhh....I didn't "assume" anything. I'm just making conversation because I though the results were interesting. I'm not going to carve dimples in the bottom of my Scarab, I'll leave it how the engineers at WellCraft left it.

[auguste]

Chris . . . interesting . . . thanks for sharing the ideas

[Fubar512]

Golf balls are spheres. They benefit from turbulent airflow, as opposed to laminar airflow: http://wings.avkids.com/Book/Sports/instructor/golf-01.html

Also, look up "area rule aerodynamics"......makes for interesting reading, and food for thought.

[Blitzen]

Interesting thought Chris,

I read an article about racing sail boats awhile back that was suggesting a boat bottom that was somewhat rough and not perfectly smooth would aid in breaking the surface tension of the water clinging to the bottom as it moves and would actually make it faster. Since then I no longer worry about the paint stipple I get from the roller when painting the bottom. Not sure if it works or not but I haven't lost any speed.

[Fubar512]

Cool little factoid: Water is, at minimum, 829 times denser than air at sea level (it depends on atmospheric pressure). Based on the fact that:

At 20° C Water density is 998.2071 kg/m^3

At 20° C Air density is 1.204 kg/m^3

Another cool (or useless ) factoid, courtesy of the wikipedia:

Although "the speed of sound" is commonly used to refer specifically to the speed of sound waves in air, the speed of sound can be measured in virtually any substance. Sound travels faster in liquids and non-porous solids (5,120 m/s in iron) than it does in air, traveling about 4.3 times faster in water (1,484 m/s) than in air at 20 degrees Celsius.

Edited October 23, 2009 by fubar512