Abuse it…
Once you’ve got some motion, call it kinetic energy if you like, you can abuse it anyway you like. Burnsie’s pictures, neat as they are, are of a rider burning up some excess kinetic energy, and trading some kinetic energy for potential energy during parts of the maneuver. Potential energy here refers to the energy that comes with position in a gravitational field. Admittedly, the fellow has some nice moves, and this kind of skill is very much apart of ‘Surfing’ nowadays, but its not what makes surfing unique.
Unique…
The essence of what make surfing unique dynamically is best appreciated during trimming –i.e. when a surfer is attempting to maintain position, perhaps because he’s or she’s in a tube, for instance. In these circumstances, the surfer is neither climbing nor dropping to any significant degree; yet they must maintain a given position and velocity.
Always there, but sometimes its doing more than just keeping you above the water…
Planing is always present. It’s surely present in Burnsie’s photos, but its definitely not propelling the surfer in any significant way. Planing just refers to the transfer of momentum from the flow of water to the surfer/surfboard system. Sometimes that transfer is just providing a dynamic lift (you could say dynamic buoyancy, but buoyancy tends to refer to hydrostatic lift – its that stuff Archimedes spoke to a while back), and sometime more.
If when you read or hear the word ‘planing’, and a high speed hydroplane with a 90 hp Merc comes to mind you’re not alone – limited in your appreciation for the meaning of the term, but not alone. Savitsky has sketched the basics of the phenomena for us (… okay, maybe just me…)
But this still doesn’t explain how planing could provide propulsion. So here’s how.
Oh my… all I did was rotate the diagram? Disturbing huh. The important bit is to check out the force vectors, a component of the one emanating from the plank is now point in a forward direction. This is what is going on during trim – that unique interaction that makes surfing ‘surfing’ and not skateboarding or snowboarding or skiing or etc.
Summing up…(big finish here)
So lets sum up, there’s ‘Surfing’ which involves just about anything you can do with a surfboard, once you’ve got the kinetic energy (energy of inherent in mass in motion), and then there’s surfing which dynamically involves something called planing, which when the board’s bottom plane is positioned right, allows the surfer to capture the momentum of the flowing water in a wave-form.
Design is concerned with both: your average garden variety non propulsive planing –i…e. when you’re just skimming along the surface, whether you are dropping or climbing or turning; and, during propulsive planing –i.e. when you’re utilizing the flowing water in a wave as a means of acquiring momentum.
Notes for the Outraged?
How dare I suggest that what the surfer is doing in Burnsie’s photos is not unique to surfing regardless of whether or not the word is capitalized? Because you don’t need a wave to do it, though something wet would be recommended. Water skiers do it all the time, though perhaps not exactly so, but definitely without the need of a wave, nor boat, for that matter, at least once they let go of the rope. Water-skiers also plan. Hell, a lot of things plan, but surfing is unique in its exploitation of the phenomena to acquire propulsion. That said, it doesn’t diminish the skill needed to do such things.
kc
PS
In the Savitsky diagram, see the little bit of flow that seems to be shooting off in the direction from which the flow is coming? That’s called, in planing circles, the root spray. In other circles (or forums, which shall go nameless for now) its often called wake. The point being that ii is the origin of most of the ‘wake’ or white stuff(?) you see while watching a surfer, especially when he/she is in trim. In Burnsie’s shots there a lot more going on, but in trim, that’s where most of the white stuff is coming from. It plays a particularly important role during noseriding.
