Where did you surf today ?

[buddy]

Have you run it as a tri-fin at all?

[steve shearer]

no, keep meaning to, but it feels so good as a quad.

[Cranked]

tbh, I really laid that out as a bait for someone a lot smarter than Loof

I'm not that smart guy, but the channels or concaves serve to constrain the water flow under the board, which is analogous to the large diameter pipe flowing to a smaller diameter pipe of the BERNOULLI'S PRINCIPLE examples.

So the velocity of the water flow under the board increases. One of the repercussions of the increased water flow under the board must surely be an increase in the friction of the board moving across the wave face.

Wouldn't this increased friction tend to slow the board down?

[steve shearer]

So the velocity of the water flow under the board increases. One of the repercussions of the increased water flow under the board must surely be an increase in the friction of the board moving across the wave face.

Wouldn't this increased friction tend to slow the board down?

No, the "repercussion" of increased velocity of water flow under the board is that you go faster and there is more lifting force available.

[crabmeat thompson]

Didn't surf - looked craptastic

it was a marathon of paddling. paddling over that freaking outside bank. then paddling south against the sweep.

all for some low tide close out gurglers ... haha

[Nick Carroll]

tbh, I really laid that out as a bait for someone a lot smarter than Loof

I'm not that smart guy, but the channels or concaves serve to constrain the water flow under the board, which is analogous to the large diameter pipe flowing to a smaller diameter pipe of the BERNOULLI'S PRINCIPLE examples.

So the velocity of the water flow under the board increases. One of the repercussions of the increased water flow under the board must surely be an increase in the friction of the board moving across the wave face.

Wouldn't this increased friction tend to slow the board down?

mate that's not what happens -- all the Bernoulli stuff -- it's just lift. the water is not constrained so much as redirected, and the pressure of the redirection supplies the board with lift. Lift=speed.

deep single concaves are faster than channels -- the pressure on the concave curve is more sustained than the pressure on the inside edges of the channels. But channels feel the wave better -- the extra edges work a bit like rail edges, giving you a lot of feedback about what's happening underfoot.

[Beanpole]

You guys and your Bernoulli Stuff. I thought it was all about fractal geometric inversion.

[Cranked]

tbh, I really laid that out as a bait for someone a lot smarter than Loof

I'm not that smart guy, but the channels or concaves serve to constrain the water flow under the board, which is analogous to the large diameter pipe flowing to a smaller diameter pipe of the BERNOULLI'S PRINCIPLE examples.

So the velocity of the water flow under the board increases. One of the repercussions of the increased water flow under the board must surely be an increase in the friction of the board moving across the wave face.

Wouldn't this increased friction tend to slow the board down?

mate that's not what happens -- all the Bernoulli stuff -- it's just lift. the water is not constrained so much as redirected, and the pressure of the redirection supplies the board with lift. Lift=speed.

deep single concaves are faster than channels -- the pressure on the concave curve is more sustained than the pressure on the inside edges of the channels. But channels feel the wave better -- the extra edges work a bit like rail edges, giving you a lot of feedback about what's happening underfoot.

I was reaching out to Steve, he just needed someone to disagree with him.

...mate that's not what happens -- all the Bernoulli stuff -- it's just lift"

Ummmm, that is the Bernoulli stuff

Funnily enough I was just at a surf shop and someone had just traded an MC with the deepest concaves I've ever seen. The comment from the owner was that it was at times the best, and other times the worst board he'd ever owned

[steve shearer]

no, Nick was saying that the upshot of bernoulli is lift, not drag.

btw, it's still debatable- and this is what i thought you might pull me up on Cranked- whether the Bernoulli effect is applicable to the hydrodynamics of the surfboard.

[Cranked]

I just threw in drag. Its definitely a result of movement of any fluid over a surface, it is not the result of the Bernoulli effect

The Bernoulli effect is what enables an an aeroplane to fly for god's sake. The movement of the air over the curved surface of the wing is what produces the lift, so the Bernoulli effect is going to be happening on every curved surface of the board that is in contact with the moving water

[steve shearer]

so the Bernoulli effect is going to be happening on every curved surface of the board that is in contact with the moving water

incorrect.

[Cranked]

so the Bernoulli effect is going to be happening on every curved surface of the board that is in contact with the moving water

incorrect.

There are a number of things happening as an airplane wing slices through the air. First, the angle of the wing (the “angle of attack”, as it’s called) means that some air hits the bottom of the wing, pushing it upwards. Meanwhile, some other air compresses together as it moves up over the front of the wing; this air then rushes down the far side of the sloping top, pulling some of the air above it downwards as well. Thus, a huge amount of air is moved downwards, and as the wing pulls the air down, the air pushes the wing back up according to Newton’s Third Law. This lift force can also be understood using Bernoulli’s principle and some calculus – the quickly-moving air above the wing does indeed result in a drastically lowered pressure.
There is, of course, quite a bit more to be said about how to keep a plane in the air – the angle of attack must be big enough to generate lift but not so big as to result in stalling, for example, and it has to match up with the plane’s speed and the density of the atmosphere – but that’s the basic story.

Bernoulli’s principle is one way to look at what’s happening with an airplane wing, but most explanations that use it to explain lift oversimplify the situation to the point of being incorrect.

As I said, it’s the combination of air hitting the bottom of the wing and the compression + downwards acceleration of air on top (plus some other crazy fluid-dynamics stuff, probably) that gives the wing its lift.

[steve shearer]

No, I'm not saying bernoullis principle doesn;t apply to an airplane wing, I'm saying you can't apply it to every curved surface on a surfboard that is in contact with water.

[alakaboo]

You think you can turn physics on and off?

[tootr]

Surfboards are ALL about physics.
Bernoulli Effect
Doppler Effect
Coriolis Effect
Placebo effect.

etc.

[steve shearer]

You think you can turn physics on and off?

no, just saying that the lifting force on a surfboard (bottom) is not due to the pressure differential caused by water flowing over both the top and bottom of the board like a wing foil.

fins, to a certain extent yes.

[steve shearer]

Surfboards are ALL about physics.
Bernoulli Effect
Doppler Effect
Coriolis Effect
Placebo effect.

etc.

Toots a lot of your genius has gone criminally unrecognised today.

[Cranked]

Where to start? The bottom of the board is a number of foils determined longitudinally by the rocker and transversely by V, roll, concaves, etc. with water moving across it in many different directions as the attitude of the board and its relationship to the wave continually changes. The rails and fins are also foils. Everywhere theres a curve and water moving over it there is a bernoulli effect