Slater Held Up By Toe'sters?

kcasey · June 2, 2009, 11:45pm

The above picture is of Slater hauling ass. He’s obviously on a gun. I can’t say for sure, but its likely a safe bet that he’s got a tri-fin setup.

There are a few things about this shot which I find interesting (aside from the fact that it’s unlikely I’m ever gonna be in a similar position.) In particular they related to the spray or wash emanating from under his board.

The Spray Root

The spray root is that part of the flow that is stopped dead or sent off in the opposed direction than that of the incoming flow. You can see it in the diagram of planing below.

Below I’ve drawn a line in the Slater shot right across the board to indicate what I believe marks the beginning of the wetted bottom surface of Slaters board, or what you could call the spray root line. Not much surface area is in play. Which is consistent with the high flow rates -i.e. higher flows, less surface area required to generate a given force.

Again this is my take on this snapshot, but if you look hard (blow up the shot if you can) you can see that the wash coming out from under the board is literally dropping straight down the face. Poor wash, Slater killed it!

But what's up with that next line of wash as you move back from the spray root?

Lateral Fin Mayhem

Mayhem may be a bit dramatic, but I’m inclined to argue that the toed lateral is shaving off a shit load of flow and that’s what is producing the effect. I’ve drawn another line in the picture below to indicate which wash line I’m referring to.

What is neat is that the crest of this wash, I guess it’s a wake of sorts, is also dropping pretty much straight down the face, though it seem to dance a little before doing so. Which is pretty cool, if my ‘why’ is correct (otherwise things will get uncool fast.)

The flow up the face will change depending on where you are on the face – whether you are out more on the shoulder or closer to the peak. Closer to the peak the flow is more upwards than forwards, out on the should its less so – how much depends on how far out you are. The changing nature of the flow is continuous. The flow being cut off by his lateral has more forward velocity than the flow it then meets as it comes off his fin, the consequence is that it literally breaks like a little wave. Okay, maybe a strange little wave, anyway it shears off. Chances are the laterals are also canted to some degree, so you've got that contributing too.

Big Finish? … hardly.

All that fin interaction costs something. That is, shearing all that flow and sending off in another direction cost something - and I believe that something is drag. The question then is why would that be desirable?

Surely running a single fin would be less of a drag? And some do exactly that. But I would contend that if they do, their posture and position on the board would be noticeably different from that of Slater's – and not just because Slater has a natural body genius. Sure, Slater is hauling ass, but I suspect that his brain is telling his body that you don't want to get to far ahead of 'it'. He riding his back foot, but my guess would be a lot less than someone trying to achieve a similar position on a single fin.

Its amazing what a little fin drag can do.

kc

wildy · June 3, 2009, 1:52am

Good observations and description.

There is also the force of the displaced water hitting the inside face of the outside fin. It may be small but it is there, and due to it’s action would be trying to push the tail away from the wave face, which isn’t really good as it’s opposing the purpose of the inside fin. Some people say it’s channelling the water between the fins creating drive.

Surely Kelly is wanting to go as fast as he can but with enough control to slow down and stay in the tube. Fins really should not be the drag factor to achieve this. Fins should be designed for control, hold and drive and create as little drag as possible. I don’t think anyone wants a board that’s fin characteristics means it is constantly wanting to slow down.

Board design still has directions to go we haven’t seen yet.

deanbonkovich · June 3, 2009, 5:43am

His outside fin is half engaged (inside fin fully engaged) and there’s a single fin in the middle trying to grab the tail and pull it up the face. Otherwise known as the joy of riding a thruster in steeper waves. You don’t need to surf Pipeline to appreciate that one. Either stick 'em in the middle or on the rail. Not both.

kcasey · June 3, 2009, 11:47am

Drive as in propel? Maybe. I know it’s getting old, but damn if this term isn’t driving me nuts (and here I’ve used in the sense of propel.) But you’re right about the fact that there’s likely more going on than my ‘lumped’ analysis might suggest.

Over time, I’ve been led to conclude that the major difference between single vs multiple, especially when toe and cant is introduced is about drag. The kind of drag we are dealing with here is proportional to the velocity of the flow squared. Both types offer as much, but toe/cant allows the designer to set both a base level of drag as well as adjust how fast that drag increases with increasing flow.

There aren’t that many ways to slow down a board to choose from - shifting you weight rearward being the major technique. But if you shift you weight rearward you impact the boards bottom presentation to the flow and orientation of the board in general. Starting off with some additional drag, and then having it function in a way so as to increase with increasing flows is sort of a optimal solution, given what is available. Remember the option to sit on the tail doesn’t go away, it’s just that with toe/cant a little goes farther, that is you don’t have to risk a dramatic change the orientation of the board with respect to the flow, at least compared to when you’re running with a single.

What is achieved is that it allows the surfer get more bang for his postural changes, hence they need not be as extreme, especially during precise trim maneuvers, like in the Slater photo.

Toed and canted system aren’t really meant for those more interested in surfing out on the shoulder, they’re meant for those seeking to dance about in that critical zone of higher flows.

It’s a design choice and I believe, one that has tended to suit modern surfing style and technique for the reasons I’ve stated above.

kc

kcasey · June 3, 2009, 12:02pm

I understand that’s your preference, and sure, the tri-fin setup may not be the perfect solution for everyone or every wave, but it does offer an alternative solution to something I’m not even sure many surfers even see as a problem, as do twins, quads, etc.

Fins are a great way to stay engaged with the flow through the strategic application of drag. Perhaps you don’t need or want the additional help, or perhaps you see it as just getting in the way more than helping, which is cool. Hell, skimboarders who manage to get into shorebreak seem to manage. As does that Barbados guy surfing a sheet of plywood(?) who’s picture appeared in the recent ‘bizzare’ but true thread of surfboard anomalies.

There are downsides to every design choice, the 'big picture' evolution of surfboards has been driven by finding optimal solutions that tend to do the job in general.

So have some patience, and remember at some point in our evolutionary past we lost our prehensile tails. Sure our asses would be forever exposed, but wiping took a big leap forward.

kc

ps.

You've got to love that photo of the Barbados guy. Check out the spray root and other line of wash coming from under his board, as well as where on the board his is. Now here's a man who knows how to use a rail.

thrailkill · June 3, 2009, 2:59pm

Note the right foot heel-drag, on the inside rail. Same trim position can be seen frequently @ Pipeline. edit: my right, his left!

TaylorO · June 3, 2009, 3:57pm

Interesting thoughts on all the fin stuff, but I’m more stoked on the fact he’s riding a nice semi-gun, as opposed to the little things, and still in the pocket… Ha! Bet it made catching it a little easier…

kcasey · June 3, 2009, 7:22pm

I'm not too sure I'll call what he's riding a semi-gun, more like a semi-wall... and anyway, Slater is not from Barbados... wow Taylor, off the mark a little on that one or what?

Then again, being from the East Coast (US), we don't see a lot of semi-guns, so maybe it is a semi-gun... I just would have thought they'd have a bit more rocker. (Is Slater really from Barbados? I thought he was from some southern state on the East coast? He also looks different from when I saw him on Baywatch.)

... oh, wait a minute, you're referring to the picture in my original post... in that case, nevermind.

kc

kcasey · June 3, 2009, 7:49pm

Are you sure about the edit? I think you were right initially. His left has got that toe action going on. I can’t believe he’s got his left fully planted on that board. Then again, its not like I’ve never misread a photo.

Hey wait a minute, this isn’t some California thing… you guys vote on some sort of proposition that changed the way everybody refers to handedness… that’s just going too far… I hope this one doesn’t catch on nationwide … I’ll have to re-label all my shoes.

kc

TaylorO · June 3, 2009, 7:58pm

I’m not too sure I’ll call what he’s riding a semi-gun, more like a
semi-wall… and anyway, Slater is not from Barbados… wow Taylor, off
the mark a little on that one or what?

???

I don’t know anything about Barbados.

My only point is, I like to see a longer board, 'cuz it’s my preference, so I can delude myself that it lends credit to my personal hypothesis…

kcasey · June 3, 2009, 10:05pm

amigo, I was joking… apparently a lame joke, but joking… but I got and get your point… and I don’t know dick about Barbados either.

kc

TaylorO · June 3, 2009, 10:38pm

Ahhhaa sorry - You gotta excuse my Asperger’s… I get it now, the other guy, on the door… “Never mind…” Ha!

janklow · June 4, 2009, 2:20am

A fluid flowing past the surface of a body exerts a force on it. If the fluid is air, the force is called an aerodynamic force. Lift is defined to be the component of this force which is perpendicular to the oncoming flow direction.^[1] It contrasts with the drag force, which is is defined to be the component of the aerodynamic force parallel to the flow direction.

Surfboard bottoms lift, as do fins.

(Lift = drag) = false.

(Primary function of surfboard fins is drag) = false.

http://en.wikipedia.org/wiki/Lift-induced_drag

etc.

BTW, “drive” is lift.

kcasey · June 4, 2009, 6:27am

The thread attempts to address the role of drag in different fin systems.

kc