Roy,
Interesting interpretation. I’m actually not sure what your diagram shows. Perhaps you meant what I’ve diagrammed in figure 1 (copied from the reference indicated). When you are trying to get a sense of what’s happening, it helps if you remember to start in the trough, and try to visualize the wave as coming towards you.
Kevin
Kevin,
Be careful with your frame of reference. From your figure 1 it appears you are considering the velocity of a water particle to be relative to the earth, not the wave. However, your analysis of the flow against the surfboard can only be done relative to the wave itself. What I mean to say is the whole system, which includes the surfboard, rider, and wave, is moving toward the beach at the same rate. The surfboard has velocity relative to the wave. The flow across the board is relative to the wave. The entire analysis must use the same frame of reference to be valid.
I’m still interested to know how you came by the Savitsky paper. It’s been out of print for some time.
Paul
Paul,
I am considering the velocity of the particle relative to the Earth, and the surfboard relative to the same. None of the equations are relative with respect to the wave. The vector diagram that shows the propulsive force is a snapshot (see above posts), I’ve put nothing to motion.
I disagree about your point requiring the analysis be done relative to the wave, at least at this point and given what I have tried to address. The only reference I’ve made which involves another point of view is when I have referred to the generated motion that the propulsive flow produces. If you want to take it a step further and put the whole thing in motion, excellent. But I don’t see the requirement at this point; the forces will exist in any inertial frame.
Figure 1 is appropriate; if you start in the trough, say between points 2 and 3 in the diagram and let the wave come towards you. Of course this is a model of a particle in a deep-water wave. Its profile distorts as the wave shoals, however the general trend is the same. But let’s consider a point a little above point 3. Here the particle is moving forward (direction of propagation) and up. I indicate roughly where such a particle might be in Figure 2. I’ve also drawn in the up and forward velocity components of the particle.
I came by the Savitsky paper quite some time ago. (I believe I mentioned this is a response to a post in the ‘Dynamics – Surfing the Force’ thread.) I discovered Savitsky after having read a section of an Australian fellow’s PhD thesis on Surfing - which he had made available on the Net. At the time, it wasn’t my impression that he had used Savitsky’s treatment to explain propulsion in surfing, but rather as just another high speed planing treatment (say, during a big drop.) I no longer have Savitsky’s work, nor the PhD thesis.
Thanks for the interest,
Kevin
Thank you Mr Kotzebue.
I concede this:
that there is a flow toward the wave in the trough which can pretty definitely be pushed against during a bottom turn,
that there is flow up the wave (given enough height of the crest and speed of the wave, giving face curvature and flow acceleration) which since it is accelerating oncoming flow toward the surfer and he is having his tail lifted and gaining forward momentum, can be used to get up and planing when dropping in, (longboarder, at bottom of wave, etc)
or stay up after an radical face gouge/braking maneuver,
also that the throwing lip can be deflected off.
But when you start out and end up saying that the whole shot is due to a “propulsive” flow force, show energy and particles moving in ways that suggest they transmit energy ahead/outside of the waveform, and thus that surfing is totally different than any other downhill board sport you’re …
Sorry janks,
I most definately do not agree with you there.
I think the “propulsive force” KC is talking about is the sum of all the forces involved (not just the upward motion of the wave). I believe that the main part of this total force is harnessed from the wave via gravity (the whole potential energy thing).
I reckon that the upward force in the wave can lift the board up higher, where it can, again, harness wave energy via gravity (i.e. potential energy). Another mechanism for this might be rider input in conjunction with momentum. To be certain there are differences between the two, but there are certain similarities - potential energy!
At it’s most basic wave riding is different to downhill boarding because of the energy sources. With downhill all the potential energy comes from however you get to “the top of the mountain”. With wave riding a good deal of it definately comes from the wave.
I didn’t see where he said energy is outside the waveform? If you remember exactly where that is, please let me know.
Anyway all, still folloing this one closely. Interesting stuff (as I keep saying).
Sorry, the diagram has arrows that point out from the surface–may be just his diagrammar is bad, but it looks like and sounds like when he speaks of propulsive energy imparted to the board he’s saying that somewhere, the board is being made to go faster, as a matter of course, as a matter of plane impact, extra to the wave’s other combined energy, the combination of forward and gravity like you said.
There is flow toward the wave as hydrological suction occurs and it must be there when you bottom turn
The board sports connection is just the gravity pull and how we direct laterally across it and push against it–a huge component of surfing’s energy, like I say, and, the forward motion is a good deal of it and renews the grade which we ride down…
better?
(Anyway, was the fact that a wave moves forward supposed to justify flat bottoms somehow?) (Concave bottom if carried to the rail allows more penetration and lift and focuses lift toward the rider’s heels or toes, a good thing if you want to exploit it)
in the last twenty five years ive surfed
ive seen no conclusive evidence that channels or concaves make a board faster or better
and that every shaper will tell you they do something different .
and 99 percent of the flock will agree with them!
and wouldnt have a clue on even the basics of the thoery except whats fed to them by
magazines
what the pros are riding
what the shaper tells them.
oh they are 100 kg and riding 6 2 and 18 1\2 wide
but they got concaves so they are gunna rip
NOT
still
th more suckers riding the wrong equipment
the more waves for me
so bring on the concaves and every other misleading design element.
most people just need a thicker/wider board
so bring on the concaves and every other misleading design element.
ouch
ive seen no conclusive evidence that channels or concaves make a board faster or better
BREAKING NEWS!
PARADIGM SHIFT! First Black Monday, now this: "Shock waves were expected to again begin rocking the surfing world today as a guy named “silly” on the internet today informed the Swaylocks.com community of backyard surfboard shapers and anyone else who would listen that they’ve been riding the WRONG EQUIPMENT and that CONCAVES AREN’T PROVEN TO WORK.
Prominent shapers could not be reached for comment. None of the pros on the WCT or surfers in any other competitive series worldwide had any comment.
Likely they are simply shell-shocked by the important announcement and its ramifications.
“silly” says that he actually expected this, that his announcement would appear to fall on deaf ears, “not because it’s not absolutely verifiably true, but because the surfing world community is a bunch of bloody sheep and the pros and shapers are in a massive worldwide conspiracy. You’ll see.”
Approximately 100% of the advanced dynamic surfers in the world use boards with bottom concaves, but that could be all about to change. Stay tuned.
: )
I like concaves, especially on boards with more rocker… . .they go well with tunnels too.
spent half the night thinking about flow in the wave, now too tired to type, almost !
.
This is just a more elaborate diagram of the velocity profiles of the particles in a deep-water wave. It’s important to remember that each particle will travel in its own path. Here the paths are simple circles, which is not exactly the case even in deep water, nevertheless they are approximately so in deep water. As the wave shoals (enters shallow-water) the profiles will change, or distort.
i thought it was 99 percent
but a guy called “janklow” just verified it was 100
have you been sitting on encyclopedias
or do you just wipe your ass with the pages 
Of all the aspects of board design that ive seen make a “difference” to the “Average Surfer”,
Concaves arent one of them
doesnt seem to make them surf faster.
or better
or catch more waves
or get more barrels
or paddle better
etc etc
etc etc
etc
so they must be really really important.
far more important then…
let me think,
im just a backyarder mind you so this is just a guess!
how about this one.
correct volume for weight and abillity?
hmm, windsurfers seem to have figured this one out years ago.
oh well i can get this toxic, 18 inch wide two inch thick
fall apart piece of shit that will last me 1 year if im lucky
with plastic fins
but im gunna rip the shit out of it.
cuz its got concaves!
yeah bring em on
concaves
im ripping now!
maybe someone with your outstanding surfing ability
would notice such subtleties in modern surfboard design,
And would notice the extra burst of speed(and extra wave count) you get from single to double with a V.
no one “proved” to me they work
and i cant really notice the difference.
and seen as this is a public “design forum”
it is my prerogative
as is Kcasey
to state my opinion,
whether true or misguided.
didnt you call someone a kook before?
so how do you manage to fit in being a physicist, pro surfer,literary genius
and still manage to have time to post here and build boards?
bro
ps
craftee
its is most likely im wrong!
but for me personaly
i not 100 % convinced about concaves!
flat is fast
stiff fins
nice and wide
pretty thick
I dont see any pros riding what i ride
but who cares?
ill never even get close to that ability
and i think that people need to ask themselves
as they fudge takeoff after takeoff and get caught behind section after section.
and spend three hours getting out the back
and only get a couple of waves when its crowded.
“why arent my concaves working for me?”
and i can tell them
"bro .you just dont have the right type of concaves,maybe you should try single
all the way through.Im going left by the way!"
kevin
im sorry for hijacking your thread with this bs
Don’t get in a huff, I was kidding you a bit
The idea is that, when you make a board that’s the right 3D’s, (for a given surfer and his/her abilities, break, aims) you increase mechanical advantage by putting a bit of concave in, out to the edges, by increasing rail penetration and directing water flow under your feet rather than having most of the lift happen at the rail, where there’s less leverage
but yeah, flat is fast, its just not necessarily the most advantageous in turns,
It’s all depending on what your aims are–I just thought your assertion a bit dubious
Thanks for the compliments–I’ll see you later
NURSE! Can you let me out now?
( :
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
<------------<---------/----------<-----------<
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Is the above what you’re trying to get across, Kevin? Where “/” is the trimming surfer enjoying lateral propulsion extra to the forward motion of the wave and gravity’s combined energy?
If it is, I’d think effective proof would be given by that ^^^^^^^^flow’s velocity relative to the crest’s vvvvvvvvv forward motion,
measured,
in an acceleration formula,
to prove a significant relative acceleration is effected by the curve of the face,
such that the forward motion of the overall waveform and gravity aren’t the whole ball of wax,
wouldn’t you?
(Paul, I was thinking some, and it’s illustrative that several different kinds of airfoils have extendable forward edges or fixed forward down extensions to effect an underwing concave profile, for enhanced lift during takeoff, landing, slow speed flight, being that the rail of a surfboard in trim is constantly doing the same sort of thing as the leading edge of an airplane wing landing, just that you’re riding that leading edge lengthwise as a rail. You have to understand how it works and engineer the wing right to take advantage of it though. So picture such an airplane wing being ridden with that extended/concaved leading edge as your rail. Now, without a concaved bottom, if you make that edge thick and round enough, the flow over the curve will effect higher speed flow off the apex of the rail, and thus enact a low pressure and suction/lift component on top of the apex–Tom Wegener talks about this on his website–but it is inducing drag, and at higher speeds, the flow goes turbulent and slows you down or releases and blows out–Wegener talks about this too. Now for shorter boards, if you can make that rail thinner and get just as much purchase by concaving it to the edge–you can penentrate the rail and direct a good flow volume inward where the rider can push off it by having more leverage with his feet.
I’m not a physicist, I just used to fly, and I now spend a LOT of time thinking about flow entry and release–but Kevin has got me thinking about the wave curve flow-acceleration factor–I just want it quantifed, and terms better defined)
let’s see what happens to water paricles in a wave which is breaking please.
.
I’m actually not sure what you’re point is, but that doesn’t mean its not an important one.
Also, I’ve looked at what I written so far and I’m not sure I could have been clearer without absolutely boring the crap out of people, which I’m sure some feel I already have. If I was to do it again I might restructure the presentation, but I think the points are clear enough.
I’ve read you’re comments and my sense is that you disagree with much of what I said. Excellent, design for what you know and feel, which is something, I bet we both can agree on.
Thanks,
Kevin
Roy,
I look forward to seeing what you come up with.
Kevin
thats an interesting diagragm!
im not in a huf
and relized half way through my post that you were kidding
ive got to expect that sort of response when i make statements like that
it was late
i was buggered
sorry
(i think we both sit on encyclopedias)
still, im very dubious about the average explanation i get of the function of slight concave.
yours seems reasonable enough
heres a question
what if you were to design in extreme concave into the bottom of the board(an inch deep)
does the rail and v now act as a type of fin?
does it still have the same function,yet amplified,of the shallow concave?
or is is it now working in a different way?
