Drive Defined?

General Discussion
1

Rather than hijack Kevin Casey’s tome on Slater’s wakes, I thought I’d put the question to the all of you. When someone starts blabbing about “drive” in surfboard or surfboard fin design, what are they talking about?

I may be waaaay off but in my mind “drive” simply means the ability to make large radius turns. You use this design trait to “drive” around a section or “drive” down the line. You can add “drive” to a board by reducing the curve in the outline, reducing the rocker in the tail, and using fins with longer bases.

I’ve really noticed it by swapping out a 9" Liddle flex for a Greenough Stage 6 in a stubby single fin and keels for MR twins in a narrow fish. The keels and Liddle flex stayed up on a rail and held an almost straight line (seems like it when you are riding). There is a feeling of the board following through without any additional input from the pilot. Using the baseless paddle Stage 6 and Mark Richards twins (who’s base is about 1/2 the keel), the boards were twitchy and a bit washed out and that “follow through” was totally absent. The Stage 6 and MRs were alot easier to break track and turn shorter radius turns (as they were designed to do).

I’ve never felt “drive” had anything to do with propelling a board, trimming, or tapping into the unseen forces of somethin’ for nuthin’. Maybe I’m wrong…

2

Hi Lee,

Interesting question. In my mind, drive is the acceleration when the board is weighted, not necessarily on a turn.

Imagine the perfect bottom turn… tucked down low to the board… hand dragging on the face, and board hard on a rail…as you reach the bottom of the wave you focus your eyes 20 yards down the line and extend your legs, pushing against the force of your speed. That acceleration is drive in a turn.

Now your bottom turn has brought you up to a high line and you are racing to beat the section ahead of you. With finess, you set your edge to a feather and crouch. This time the board is in perfect trim, with its only direction down the line. Pump your legs to weight and unweight, but this time just to build speed along the wall. This time your actions are working against the water moving up the face of the wave. You are accelerating or driving in a straight line.

Drive is you ability to work against the flow of the water to build speed.

3

I like the bottom line, everysurfer.

Boards and fins, balance, weighting and unweighting, all working together to give you projection, acceleration and speed, going straight or turning hard.

4

Hey Lee. If you ask me, and at the risk of repeating myself, it’s absolutely contained in the definition of lift (and Wikipedia’s related articles) + the experiences you guys describe above. Everything I read above screams lift to me-- planing lift and foil lift. Refer to… mainly Newton, I reckon.

http://en.wikipedia.org/wiki/Lift_(force)

http://en.wikipedia.org/wiki/Planing_(sailing)

http://en.wikipedia.org/wiki/Planing_(sailing)#How_planing_works

sorry those aren’t hot links–cut and paste style

5

tome? … ouch

… I would have went with ‘tomette’, as in something shorter than a tome, but seemingly just as long when you try to read it.

Couple of intersting takes on the term [drive] so far - hopefully others will jump in.

Nice thread.

kc

6

I tend to think of drive as “road holding” is used for a car (or a skateboard for that matter). Loosen the trucks to the max and you get something that is extremely manoeuverable at low speeds. But if you use this same set-up and go for a downhill run, you’ll very quickly experience wobbling and, ultimately, the crash of your life. Instead, tighten the trucks to the max and you will get a fine downhill speed model (but don’t try to do sharp turns at low speed with it).

Going longer and narrower in outline and curvier in rocker together with more spaced out cluster of fins, more raky fins and so on will build up drive but will decrease manoeuverability (again, at low speed: such boards are quite “manoeuverable” at high speed). Just my two Euro cents…

7

I see it much like janklow and everysurfer…

Drive is the ability to capture flow with board and fins, and use it to build speed. As any given design encorporates elements that increase that ability, the price that is paid is sensitivity or manuverability or responsiveness… and we can start a few new threads to talk about these terms, I guess. Fin features that help capture and redirect flow for speed can include wider based fins, fins further apart, fins further back, less fin toe-in… Board design features that help capture flow are deep channels, flat rockers, increased width, elongated concaves, etc… These are not absolutes, but when used in combination with other design elements, help tap into flow and produce speed, but the cost comes in how loose it feels and how tight a radius it can make through a turn.

So when I look at some of these design features, they certainly are related to lift - like concaves and channels. Here, I’m using lift to help create speed or drive. But drive to me isn’t just speed in terms of acceleration and flat out down-the-line speed. It’s also about holding speed through a turn. Loose, responsive boards can make tight, turns, but they scrub off speed easily, and it’s up to the rider to get the board back into a place on the wave that will help them get their speed back up quickly. Drivey boards conserve speed through the turn, and so have greater projection out of the turn. This allows the board to reach it’s top end speed down-the-line more quickly, say, after a bottom turn, with less rider input, as more speed was held coming out of the turn.

Basically, to me, drive is not just how fast a board can go - that has a lot to do with the rider. Boards that are “drivey” have design elements geared to conserve the kinetic energy of motion of the board through turns by capturing and holding water flow, giving it specific direction, and minimizing the amount of moving water that spills off the fins and rails in an uncontrolled, chaotic manner.

Blah, blah, blah… lets go surf!

8

Hey Lee,

May not know what it is, but I do know what it isnt. Its modern rail surfing without any lateral drift.

9

While common meanings of the word “lift” suggest that lift opposes gravity, lift can be in any direction. When an aircraft is flying straight and level (cruise) all of the lift opposes gravity. However, when an aircraft is climbing, descending, or banking in a turn, for example, the lift is tilted with respect to the vertical and the lift is greater than, or less than, the weight of the aircraft.[

Maybe my assertion wasn’t clear without this part of the explanation broken out and highlighted. I’m pretty sure all the things bulleted above have lift in common.

10

Apparently, I’m not as polite as you [LeeV] when it comes to hijacking a thread. Here’s my summary so far. If I’ve misinterpreted anyones reply, my apologies (hopefully you’ll correct me.) I’ve obviously (and subjectively) distilled peoples responses down somewhat.

  • ability to make large turns (LeeV)
  • acceleration when the board is weighted (everysurfer)
  • work against the flow … to build speed (everysurfer)
  • projection, acceleration and speed (Wildy)
  • lift (janklow)
  • 'road' holding (balsa)
  • capture flow and build speed (nj_surfer)
  • conserve kinetic energy through turns...optimizing capture and direction of flow (nj_surfer)
  • minimizing lateral drift (crafty)

Nice stuff so far.

Nice thread.

kc

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11

Drive is the force/energy that the rider imparts into the wave/board/rider system.

There are three energy sources in surfing. 1) Gravity; 2) Wave/Water; 3) Surfer/Rider.

The surfboard designer can manipulate how the surfer’s energy is transferred to the planing and lift surfaces, thus effecting drive. For example, more rail fin means more drive.

12

Once lift, which is opposite of the force pushing down (rider’s feet) and perpendicular to the direction of mtion, is used to create forward motion, it’s no longer considered lift, in my conception of what’s going on. Technically, lifting force converted into forward force, and ultimatley forward motion, becomes thrust. In my theoretical model, drive is more directly associated with thrust, and indirectly associated with lift. But really, you can’t separate the two, I guess…

13

So are you saying drive and thrust can be used interchangably?

like the famous movie goes…“is your brother gonna shit, or is he gonna kill us?!” :slight_smile:

Fwiw, I like the term thrust more than drive cuz its what I feel.

Where did the term ‘drive’ originate?

hmm…upon further thought, I dont really like the term ‘drive’. Im goin out on a limb and say its not a valuable term.

I’ll go out on another limb and say it has mostly to due with fin setups. Ive taken boards with mediocre fin setups and some drift and have converted them with so much thrust that I over shoot the pocket with loss of speed control…“feels like” 100% potential-kinetic energy transfer.

14

I’d like continue the skate boarding analogy that Balsa started above. I can hop on a skateboard that is standing still on a flat surface, and create drive. Back in the day we called it tick-tacking. You lift the nose of the board, and move it back and forth (side-to-side). If you are really good you can do this without bringing the front wheel back down to the ground. The tighter the trucks are the more speed you can generate using this driving motion. Creating drive on a surfboard with a thruster setup can be acheive using the same back and forth motions going up and down the face of the wave. This really helps if you drop in late at a lined up point like Rincon. It gets you up to speed fast, so that you can make the first section.

When I started riding a single fin board I realized that it is much more difficult to generate drive using the same movements. I now prefer the motions of a single fin board, because it forces you to be more fluid in your turns. I am willing to give up this initial pickup for the smoother feeling of a single.

15

Good post. But that term is called ‘pumping’ not drive.

Singles are cool.

16

It is exactly lift, by definition, which definition I didn’t write, BTW. I’ll argue, which isn’t so much an argument as pointing out-- All of the acts of surfing are acts predicated by-- and centering around-- lift.

17

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

18

I agree… it all starts with lift. Even a dead flat piece of wood trimming down the line moves forward as a result of lift, as water rises up under the board. Without fins, the board has to be angled to create the forward motion, allowing gravity to do the conversion of lift to thrust. The rider balances the two forces, adjusting the angle, to stay in trim. Fins add lift, and drive, and stability, and drag, converting more lift into thrust.

19

Even with fins, you have to angle downward to trim.

20

Pumping generates speed, how much speed is determined by how much “drive” your fins provide. Regarding Swied’s analogy, when I was younger and much more energetic, I would skate with really loose trucks, I could go for miles without ever pushing off, or lifting the front truck, just by pumping, very similar feel to riding a wave, only no off the lips or bottom turns unless you could find a smooth enough bank. In that instance, the drive was the force of the wheels against the pavement (friction?), somewhat akin to roller skating in that you can’t go forward unless you push somewhat perpendicular to the direction you want to travel. Same with surfing, if you’re not pushing against the grain, you’re not generating your own speed.