Surfing Waves

jaffa1949 wrote:That's an OOPs on that, it probably isn't compression in the correct terms of physics, but the venturi effect relies on Bernoulli's principal, that the fast a fluid ( air water etc is moving the less the pressure of the fluid is. Jet engines use it where they have a big opening to the engine which then narrows down through the turbine and then reopens out just past it.
Surf boards do the same with a single to double concave The credit for modern bottom contours should be spread over a number of experimenters but the Campbell Brothers in American came up with a three fin board "The Bonzer" with the contours of the bottom then were fairly hard tapering channels with a small side bite ( although the term wasn't used then ) keel like fins that followed the contour with their cant. From my observations of Bonzers this seemed to give a greater down the line squirt of speed than anything else I observed.
Getting people to shape the contours for venturi in Australia was like explaining Mammals to Dinosaurs, and then the thruster can along and i couldn't take the idea any further. Meanwhile in the States the Campbell Brothers kept their ideas and softened the contours to single to double concave still with the fin cant.
So I recently bought a set of FCS Bonzer fins and today I tried the smaller pair and whammo great nose rding on a very small wave and lots of zip in the little perfect waves

Here is a picture of a Venturi imagine shaping a channel bottom to these contours, I was concerned that tyhe board would track and leave me having to hold the line I set on the wave but the release was great and turning was easy.
Applause to the Campbell Brothers

ventur11.gif

1973_Bonzer_plan_Surfer__Sep_v14n3p64.jpg

Look the Bonzer up a great design

jaffa1949 wrote:
Venturii effects interest me for surf boards

Rickyroughneck wrote:

jaffa1949 wrote:That's an OOPs on that, it probably isn't compression in the correct terms of physics, but the venturi effect relies on Bernoulli's principal, that the fast a fluid ( air water etc is moving the less the pressure of the fluid is. Jet engines use it where they have a big opening to the engine which then narrows down through the turbine and then reopens out just past it.
Surf boards do the same with a single to double concave The credit for modern bottom contours should be spread over a number of experimenters but the Campbell Brothers in American came up with a three fin board "The Bonzer" with the contours of the bottom then were fairly hard tapering channels with a small side bite ( although the term wasn't used then ) keel like fins that followed the contour with their cant. From my observations of Bonzers this seemed to give a greater down the line squirt of speed than anything else I observed.
Getting people to shape the contours for venturi in Australia was like explaining Mammals to Dinosaurs, and then the thruster can along and i couldn't take the idea any further. Meanwhile in the States the Campbell Brothers kept their ideas and softened the contours to single to double concave still with the fin cant.
So I recently bought a set of FCS Bonzer fins and today I tried the smaller pair and whammo great nose rding on a very small wave and lots of zip in the little perfect waves

Here is a picture of a Venturi imagine shaping a channel bottom to these contours, I was concerned that tyhe board would track and leave me having to hold the line I set on the wave but the release was great and turning was easy.
Applause to the Campbell Brothers

ventur11.gif

1973_Bonzer_plan_Surfer__Sep_v14n3p64.jpg

Look the Bonzer up a great design

Oh yes of course . To be honest though I am sceptical that the principle actually applies to surfboards. The reason being is that jet engines work because the air is heated and the expanding gases are compressed and forced backwards (like a rocket). Since the water does not expand at all, it couldn't provide any propulsion since there are no moving parts. To use a popular term "there is no such thing as a free lunch". Regardless, I am sure the concave bottoms are very fast anyway but for different reasons.

Roy_Stewart wrote:
Quite so.


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jaffa1949 wrote:BTW a lot more tank testing of the dynamics of shape rail and bottom contour would an interesting research project for someone.
Full physics would settle a lot of myths and erroneous beliefs.

jaffa1949 wrote:I 'm pretty sure that the effect is by applying Bernoulli's Principle as a lift component rather than true venturii in a cylinder as the concaves are only two dimensional and the narrowing would use the lift factor to create a low pressure at that point

Rickyroughneck wrote:

jaffa1949 wrote:BTW a lot more tank testing of the dynamics of shape rail and bottom contour would an interesting research project for someone.
Full physics would settle a lot of myths and erroneous beliefs.

Something like this would be excellent! Scientific method in the design of surfboards would be a major leap forward.

jaffa1949 wrote:I 'm pretty sure that the effect is by applying Bernoulli's Principle as a lift component rather than true venturii in a cylinder as the concaves are only two dimensional and the narrowing would use the lift factor to create a low pressure at that point

That is an interesting theory, but narrowing the contour to speed up the water to reduce the pressure would have the opposite effect: it would suck the surfboard down. I can only assume that the actual effect is minimal enough not to impact the ride to a significant degree.

I think it is the Venturi effect that makes the single to double concave work, the expanding area under the surfboard slows the water to provide more upthrust. I want to experiment with a shallow single concave that starts small at the front and widens to the tail, but alas lack the funds to do so (probably for the best).

jaffa1949 wrote:So I surf like a bee, in terms of raw physics a bee should not be able to fly, but nobody told the bee and they do, fly

One of the most elusive questions in science has finally been answered: How do bees fly?

Although the issue is not as profound as how the universe began or what kick-started life on earth, the physics of bee flight has perplexed scientists for more than 70 years. In 1934, in fact, French entomologist August Magnan and his assistant André Sainte-Lague calculated that bee flight was aerodynamically impossible. The haphazard flapping of their wings simply shouldn't keep the hefty bugs aloft.

And yet, bees most certainly fly, and the dichotomy between prediction and reality has been used for decades to needle scientists and engineers about their inability to explain complex biological processes.

Now, Michael H. Dickinson, the Esther M. and Abe M. Zarem Professor of Bioengineering, and his postdoctoral student Douglas L. Altshuler and their colleagues at Caltech and the University of Nevada at Las Vegas, have figured out honeybee flight using a combination of high-speed digital photography, to snap freeze-frame images of bees in motion, and a giant robotic mock-up of a bee wing. The results of their analysis appear in the November 28 issue of the Proceedings of the National Academy of Sciences.

"We're no longer allowed to use this story about not understanding bee flight as an example of where science has failed, because it is just not true," Dickinson says.

The secret of honeybee flight, the researchers say, is the unconventional combination of short, choppy wing strokes, a rapid rotation of the wing as it flops over and reverses direction, and a very fast wing-beat frequency.

"These animals are exploiting some of the most exotic flight mechanisms that are available to insects," says Dickinson.

Their furious flapping speed is surprising, Dickinson says, because "generally the smaller the insect the faster it flaps. This is because aerodynamic performance decreases with size, and so to compensate small animals have to flap their wings faster. Mosquitoes flap at a frequency of over 400 beats per second. Birds are more of a whump, because they beat their wings so slowly."

Being relatively large insects, bees would be expected to beat their wings rather slowly, and to sweep them across the same wide arc as other flying bugs (whose wings cover nearly half a circle). They do neither. Their wings beat over a short arc of about 90 degrees, but ridiculously fast, at around 230 beats per second. Fruit flies, in comparison, are 80 times smaller than honeybees, but flap their wings only 200 times a second.

When bees want to generate more power--for example, when they are carting around a load of nectar or pollen--they increase the arc of their wing strokes, but keep flapping at the same rate. That is also odd, Dickinson says, because "it would be much more aerodynamically efficient if they regulated not how far they flap their wings but how fast "

Honeybees' peculiar strategy may have to do with the design of their flight muscles.

"Bees have evolved flight muscles that are physiologically very different from those of other insects. One consequence is that the wings have to operate fast and at a constant frequency or the muscle doesn't generate enough power," Dickinson says.

"This is one of those cases where you can make a mistake by looking at an animal and assuming that it is perfectly adapted. An alternate hypothesis is that bee ancestors inherited this kind of muscle and now present-day bees must live with its peculiarities," Dickinson says.

How honeybees make the best of it may help engineers in the design of flying insect-sized robots: "You can't shrink a 747 wing down to this size and expect it to work, because the aerodynamics are different," he says. "But the way in which bee wings generate forces is directly applicable to these devices."

dklay wrote: I don't know as I'm good enough to know the difference!

jaffa1949 wrote:The spot was called little Noosa and is about as far way from the real Noosa as you can get on the east coast of Australia , Victoria's Mornington Peninsula.

jaffa1949 wrote:Sort of the Aussie equivalent of a bad UK day

dklay wrote: I recently came across this shaper's site :

http://www.jblairsurf.com/Home_Page.html

hunsta wrote:

jaffa1949 wrote:The spot was called little Noosa and is about as far way from the real Noosa as you can get on the east coast of Australia , Victoria's Mornington Peninsula.

I would suggest they call it "Little Noosa" cause it never got over 2ft.