I read the long thread about defining drive and am curious as to what creates it?
I know that every thing (almost) in a design is a compromise between two variables (speed/drag) (maneuverability/stability) so improving one comes at a cost.
What I was wondering is what attributes help increase the amount of drive in a surfboard (ie flatter rocker, fins further back?)
And what will be the offset of the increased drive (less maneuverabilty?)
Thanks
Jim N
Gravity has it’s part to play in creating speed. Not sure if that helps.
I don't think one can "create" drive...there is no actual additional energy created anywhere in a board, only harnessing, returning or resistance.
Curves merely make it easier to break the direction of the fall-line, like a spoon edge through butter as opposed to a knife edge...
Simplistically, it is indeed a balance of compromises between falling and control. Aft-placed fins are a control factor and in turn create greater resistance when direction changes are demanded...i.e "stiff"
And flatter rockers are faster only up to a point, because if the board is not fitting well in a pocket, it loses the source of energy.
Josh
Twin keels, six or so inch butt crack, 11 inches or so between the tips? Mike
Well put speedneedle! I completely agree. For a givin speed and curve of wave face you can only make a board that is hydrodynamic. No more that that. That is why we all have diff. sizes of surfboards. Fins that cavitate on a bottom turn or trying to muscle a flat rockered board to turn is not effecient. Flat rockered boards only are fast on plane/trimming.
Mahalo,
MW
Briefly,
Getting to the question
Since you didn’t provide your own definition, I’ll go with mine.
Drive in this context is a reference to the quality of an
acceleration, in particular a continuous controlled acceleration,
rather than a jerky and/or less controllable or less predictable one.
Gaining or loosing…
Surfing has a sort of duty-cycle; in general, part of the time your gaining
energy, and the other part of the time, your loosing energy, sprinkled with moments when the two balance.
Unlike objects hurling about in outer space, a object moving with
a constant velocity in a viscous medium, if only partially submerged
requires a force. So even if you’re
moving with a constant velocity, you will be both acquiring and burning energy
to do so.
Half the story…Sources of energy*
There are three basic sources of energy available to the surfer
surfing on a wave: what he brings with him; the kinetic energy
inherent in flow of water; and, the planet’s gravitational field.
You may see your surfing style as turning a lot, but even if done
smoothly and seamlessly, one maneuver to the next, you will be cycling
through this duty cycle. And if you’re gaining energy, that energy is coming from one of
the three sources mentioned in the last paragraph.
Acceleration
But energy is not acceleration. Energy is just a form of
accounting, it doesn’t exist. It has no pure form. It is always
associated with something like a force or relative motion. So the above
reference to three sources of energy could have been termed instead
as three basic “forces”: whatever force the surfer himself can
bring to bare biomechanically; the forces developed from changes in
the momentum of the flow of water; and, the force associated with the
gravitational field.
Since force defined as mass times acceleration, all can play a
role in drive, and surfboard design or mechanical design in general,
can be used to both harness and control each, to the
extent that each can be respectively harnessed and
controlled.
Perception
A given surfboard which seemingly provides
one surfer with all the necessary tools to harness and
control these forces, may seem less so to another. This isn’t just a
matter of skill level, but technique too. This relates back to the
use of the term drive, not all are guaranteed to experience it on
similar equipment, let alone experience it to the same degree. This
is obviously important, particularly with regards to the role of technique. Given the way some
surfer surfs, he may find that a certain design element seems to
provide him with this sense of drive at the right times. That same
design element viewed as less important, if at all, in providing a
sense of drive by another surfer.
Getting back to the question
So the question becomes, who's the market. And 'who' includes conditions, and technique. So define the market. Is it a market that wants to rip up slower mushier smallish 3-4 ft waves? Or a market that wants to survive and maybe get a little more done on 40-60 ft waves? Or any number of other scenarios.
Once the market is known, you can then start the trade-off exercise.
kc
*the other half of the story is energy sinks, or ways of dissipating energy, all of which are critical in design... but like I wrote at the beginning of the post "Briefly, "
[quote="$1"]
I read the long thread about defining drive... [/quote]
Hey jimi, it would be helpful to know what "drive" is.
I’m not sure fitting-in is all that desirable. In fact, the
essence of surfing is about not fitting-in.
In my post to jimthesaint
I stated the three sources of energy, or three basic forces. The one
which defines surfing, or puts surfing in a separate class is the
second one listed: in terms of force, the forces developed from
changes in the momentum of the flow of water. Predominately, this
take the form of the forces developed during planing – a
partially submerge object in some fluid, colliding with the flow of
that fluid. So getting in the way of that flow is critical.
I would argue that surfboards
really aren’t design to fit into the curvature of a wave face, but to
exploit that curvature in order to generate force. The ‘attack’ in
angle-of-attack suggests as much, without it I’m not sure what you
have.
As I also wrote in my response to
jimthesaint that you
are either gaining or loosing energy when surfing. This is true
because water is a viscous medium. So even if you’re trimming in a
barrel, you’re burning energy, and that energy is coming from
somewhere, and in that case from the colliding water on the bottom of
your board.
If you fit in you are ‘not making
trouble’ so to speak, that is you are not colliding with the flow,
and if you’re not colliding with the flow, you are loosing energy.
Design is about providing the
surfer with right tools to ‘not fit-in’.
kc
[quote="$1"]
I'm (edit out 'not') sure fitting-in is all (edit out 'that') desirable. In fact, the essence of surfing is about...
[/quote]
..getting barreled.
[quote="$1"]
If you fit in you are... [/quote]
..tubed.
[quote="$1"]
Design is about providing the surfer with right tools to...
[/quote]
..get BARRELED!
I guess I should have defined my opinion of the term drive - I like the 2 following definitions from the Drive Defined thread
Drive is you ability to work against the flow of the water to build speed. (Everysurfer)
Drive is the ability to capture flow with board and fins, and use it to build speed. (NJ Surfer)
Thanks for all the input - it helps me to better understand how the different aspects contribute to the ride.
Jim
Howzit jimi both of your favorite definitions include the term "build speed". To me that says thrust. Personally I think the term 'drive' is too nebulous, but thats ok.
What I was wondering is what attributes help increase the amount of drive in a surfboard (ie flatter rocker, fins further back?)
'Performance attributes' would be maximum thrust and minimum drag. 'Design attributes' can vary a lot depending on who you talk to.
Focus on fin setup and bottom edges. For example, I can take a three finner, covert it to a quad and have way more drive. However, not just anyone can make a good quad, it takes some skill and knowledge to get them right. So if you dont know how, have some one who does do it for you. You can also got more drive by switching fins - some fin designs are designed to maximize drive. Fin flex/material also plays a big role. Boards with too much rocker or too soft edges can often lack drive.
I think that in order to surf good you have to create drive.
I think that drive is the force/energy that the rider adds to the wave/board/rider system. Like how you can go higher on a swing, or trampoline, or half pipe by compressing and expanding/extending your body. You are in effect, momentarily adding or subtracting your weight from the system. This is how you create drive.
Drive is the energy that the rider adds to the system. A board that has (more) drive will harness this energy more efficiently than a board without (or with less) drive.
imho…
To me, drive is the ability to convert energy into thrust, whether that energy comes from the surfer, the wave, gravity or any combination of the three.
While doing a big cutback or driving around a section, drive is the ability to carry speed through the manuever.
Surfing is in essance a continuous transfer of energy from kinetic to potential and vice versa. The surboard (fins included) allows a surfer to utilize this energy interchange to surf the wave. Different surfers and/or waves require different tools to effectively manage and transfer energy while surfing a wave.
G'day Jim, I think the majority opinion on LeeV's [url=http://www2.swaylocks.com/forums/drive-defined]drive defined thread[/url] was that drive is speed off the bottom turn and I think Lee generally agreed with this although he didn't consider pumping to be drive. My rather anecdotal post was describing a bottom turn. I consider the word "pumping" to be a body motion rather than a board quality like drive, but believe it is related to drive - pumping allows the bottom turn to be repeated rapidly and also with extra compressive body weight thus getting a greater frequency of drive bursts and drive at an increased speed.
downwardly pushing with the legs to momentarily weight a board at the bottom seems to increase drive. It creates extra side pressure on the fin. The contributors to the [url=http://www2.swaylocks.com/forums/trade-offs-modern-toedcanted-multiple-fin-systems?page=1] modern toed/canted multifin thread[/url] explain why side pressure creates forward thrust. Although I did post on that thread an [url=http://www2.swaylocks.com/forums/trade-offs-modern-toedcanted-multiple-fin-systems?page=2#comment-1337524] analogy of a fin to a sailboard sail[/url] being subjected to greater sideways wind generates more forward propulsion, all I was doing was attempting to repeat what the others had said in words I understood.
That thread gives a fin centric view of drive and I wonder if its not just the fins that are responsible for giving that feeling of speed off the bottom turn? - but I don't know. However my experiences do correlate with what Speedy and M Woo are saying about low rocker - I once built myself a low rockered thruster (deliberately took some planer cuts out of the centre of the blank to flatten it out) - conventional shortboard thruster otherwise - board was terrible - it wouldn't pump properly - just seemed reluctant to react quickly to attempts to pump it. Twin fins on the other hand like lower rocker - this is because its best to keep the nose down and more even pressure on each foot during the bottom turn. The idea is to skate through the bottom turn with the board travelling flat using momentum from the drop rather than drive.
Aloha,
Just adding a bit to Durbs post.
“Surfing is in essance a continuous transfer of energy from kinetic to
potential and vice versa. The surboard (fins included) allows a surfer
to utilize this energy interchange to surf the wave. Different surfers
and/or waves require different tools to effectively manage and transfer
energy while surfing a wave.”
Yes, I completely agree. A diff. level of surfer needs a diif type of board. Rail speed/drive is normaly created by an advanced surfer. A begginer trims most of the time and has a harder time redirecting the energy of the wave.
Every wave has a diff. arc/face curve and speed. Getting a board to travel that on rail is what I try to achive.
MW
Aloha KC,
“Design is about providing the
surfer with right tools to ‘not fit-in’”.
I would disagree with the “not fit in theory”. When I make a board for steep hollow waves it normaly has more rocker not less. Therefore fitting into the curve of the wave. The opp. for a flat faced, slow wave. Effectively redirecting energy from a surfer and the wave with board design equals speed.
Maybe words are getting in the way! Haha
Mike Woo
They can, can't they.
It's one the reasons why I really enjoyed LeeV's Drive Defined thread and his current Release Defined thread.
Maybe it is just one's departure point. For me, you must get in the way first, then you can start backing off, or adjusting by how much. As I've mentioned above, since we're dealing with a viscous medium, motion [in surfing] is about force, and getting in the way of one [a force] is the only way you're going to get it to work for you.
So given you've got to get in the way first, if fitting-in means adjusting design to best take advantage of the conditions, then fitting-in makes sense. (You seemed to suggest as much in a prior post regarding hydrodynamic efficiency - that is, there's only so much that can be achieved. At least that was my interpretation.) It's just that I'm inclined to believe that the 'getting in the way first', which is the critical part of the argument, is too often forgotten.
In your reply to durbs, you wrote “Every wave has a diff. arc/face curve and speed. Getting a board to travel that on rail is what I try to achieve.” You also wrote something similar in another post suggesting that every board has an arc that it wants to follow (I'm paraphrasing, please correct me if I've misinterpreted.) Both have a lot of truth in them. Though I would modify the latter with 'for a given surfer and conditions', which I suspect you might have hoped would be obvious. Nevertheless, to me the words suggest a kinematic departure point, not a mechanical one. (Whether or not you intended as much.)
Consider, for centuries the trajectories of objects hurled by hand or by some gizmo were actually well understood, yet why they followed those trajectories was not understood until the mechanics or the forces involved were understood (which. in terms of human history was only recently.) Understanding the kinematics, can only take you so far.
Gee, waxing philosophical at 7:00 AM. You've got to love the Internet.
kc
[quote="$1"] What I was wondering is what attributes help increase the amount of drive in a surfboard (ie flatter rocker, fins further back?) [/quote]
in order of highest drive I rank the following three fin configurations:
1. thruster
2. single fin
3. twin fin (second generation MR style twin fin as opposed to traditional keeled fish)
I didn't mention quads because i have only borrowed a couple in 80s and they were drivy but had problems - they must have improved since then.
despite waxing lyrical about twin fin speed in my post on the [url=http://www2.swaylocks.com/forums/fish-fin-arrangements-please-explain]fish-fin-arrangements-please-explain thread[/url] they really are very poor at accelerating off the bottom and the speed I was talking about was specifically descending the wave in a straight line (and not too far down the line either - I call this the "fall line").
regardless of the configuration type I think there is an optimum position for drive rather than the further back the better. If fins are moved forward of their usual position then the board will feel squirrely if the original foot position is maintained. Although the rear foot usually moves up the board to compensate, the closer to the middle of the board the rear foot the harder it is to get the board banking on edge and the right amount of tail sink for thruster type surfing - I think the contributors on the [url=http://www2.swaylocks.com/forums/trade-offs-modern-toedcanted-multiple-fin-systems?page=1] modern toed/canted multifin thread[/url] are saying that a bit of tail sink on thruster is a good thing because it makes good use of how the water flow aligns itself with toed side fins. Anyway thats theory and I've moved fins (entire cluster and just rear fin) of the thruster back from their usual position and this seems to make the board reluctant to pump which loses drive opportunity.
PS when I was talking about bottom turning twin fins in my previous post on this thread I was talking specifically about the second generation twin and not the keeled fish
Interesting thread. I think of drive in a more simplistic way, how it feels to me: Drive is that feeling of forward thrust that occurs when you push the board's tail laterally against the water. That feeling of acceleration when, as you push the board against the wave, the wave pushes back and the board accelerates.
Lay a thruster or quad on the water and just push the tail to the side. The board will jump forward. That's my understanding of drive.
Glad you qualified that statement about twins and fish… I’ve found fish to have the most drive of all designs. What makes that so is the question posed in this thread. I believe the elements that increase drive necessarily decrease sensitivity and increase a board’s hydrodynamic form (reduce drag). Larger fin area, particularly fins base, flatter rocker, wider in the entry rocker area (puts more rail in the water allowing the bottom to capture more flow), down rails with little bottom radius (increases effective bottom, also capturing more flow when banked), straight rail line in the tail with clean release edges (ditto), little fin toe-in… all help reduce drag and increase drive. Traditional twin keeled fish have all of these attributes. They’re not so popular becasue they don’t do much else very good. They lack the sensitivity and release off the top that thrusters are designed for. But they drive like bat out of hell.
And in terms of fitting into the barrel… Fish work fantastic in the barrel. They’re flat, but short, which makes up for their lack of bottom curve. With that big ol’ inside fin, and inside pin tail, burried deep in the face they hold and drive through the barrel very, very well. Never used to think so, before I started pushing what I thought was their limits, but I know that for a fact, now. Making that drop can be sketchy, though!