Author Topic: Speed of a Board on a Wave  (Read 12931 times)

Beasho

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Re: Speed of a Board on a Wave
« Reply #15 on: May 22, 2017, 05:33:49 PM »
Here was the perspective on Matt Rott, the guy who fell.  I wonder how fast he was going  ::)   ::)   ::)

Looks like he might have added another 45 degree angle DOWNWARD.  So he took the 20 mph forward vector and added a 20 mph vertical vector giving him a a straight line 28 mph into the pit.  Sweet!

https://www.youtube.com/watch?v=CiEJpv0ALjk
« Last Edit: May 22, 2017, 06:02:34 PM by Beasho »

Subber

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Re: Speed of a Board on a Wave
« Reply #16 on: May 22, 2017, 05:58:14 PM »
Average speed 18.2mph (29.3kph).  Waaay faster average than skis on open ocean swells.  Surfboards zoom across the face of waves.  But we go for miles... :)

Apparently Faster than Robbie Too!  He only average 18.1 MPH and for a paltry 7/10's of a mile.  Kudos to you for actually bringing some NUMBERS to the discussion.

On that wave Robbie did quite a few bottom turns, cut backs and stalls that lowered his overall average speed.
It would be interesting to know what his top speed was in the sections where he had to step on the gas.
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headmount

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Re: Speed of a Board on a Wave
« Reply #17 on: May 23, 2017, 12:19:42 AM »
Downwind paddle surfers on either SUPs, canoes or skis can attain peak speeds of around 18mph so not as fast as Mavs but faster than most surf spots.   LaPerouse Bay keeps good records of his ski runs and I'm sure he's hit the red line a few times... but I guess that isn't a board.  But I've had an 18 mph spike before.  The rudder couldn't handle the speed and I crashed hard.

If you have the cajones to charge the Alenuihaha Channel between Maui and the Big Island, you might find all the speed you ever would want... but as Jack Nickleson said, you can't handle the truth.  Some of the worlds best went out there and haven't gone back for round two.

supthecreek

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Re: Speed of a Board on a Wave
« Reply #18 on: May 23, 2017, 05:14:32 AM »
Pono said:
"If you got your speed from going "down the hill" you wouldn't go very far or very fast. You can do the math, I've done it here before and explained the mechanics of the energy transfer. You could just look it up. We get energy from the face of the wave. It's nothing like skiing unless you're fond of skiing five-foot hills. Ever notice that as you cut harder across the face of a hill while skiing that you go much faster? Me either.
I got all the arguments about cutting up and down the face to go faster, which basically means those folks were sound asleep in high school physics class.
"

If there was Physics in 8th grade, then I slept through it.
But I have not slept through the following 50 years of surfing.

The belief is alive and well in us , that "pumping down the line" is the most effective way to gain speed (on the waves we ride... mega waves excluded)

Drop[/i]
coil your legs up as drop in, then "explode" the power of your coiled legs into a carving bottom turn that projects you back up towards the lip
then you drop again
Repeat the process

it is "climbing and dropping".... but you add speed by coiling and uncoiling your legs with an explosive carve back to the top.
If you have not felt this, then you have never done it correctly.

100's of video's about this technique, so apparently we are all being duped?
Does anyone believe we should just "hold the line" to go faster? (on regular surfing waves)

http://www.youtube.com/watch?v=5-6oXDMQ2ao

or....
you can simply slide sorta sideways across a wave.

Me and my insufficient physics? Why, I'm gonna pump down the line, blissful in my ignorance. :)



digger71

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Re: Speed of a Board on a Wave
« Reply #19 on: May 23, 2017, 01:19:25 PM »
Yes the "pumping" up and down the face builds speed, but not because of your leg strength.  As PB says, we get our energy from the face of the wave.  My simple understanding - when we put the board on rail it interrupts the flow of water moving up the face and propels us upward.

Without that assist from the wave it doesn't work.  Try dropping into a halfpipe (snowboard, skateboard, whatever), coil your legs, bottom turn, explode off the bottom, and climb back up the same face you just dropped into.  Let me know how far back up the face you get ;)

supthecreek

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Re: Speed of a Board on a Wave
« Reply #20 on: May 23, 2017, 03:23:08 PM »
The wave does provide the energy, which is why we surf,
but if I simply dug my rail to climb up, then drop again, it would be a lazy affair with moderate results.
If pumping did nothing, we would all surf stiff legged.


Half pipes aren't my thing, but I can certainly stand on a skateboard, in a flat parking lot and go from a dead stop to zipping right along, by just pumping my legs.

Tom

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Re: Speed of a Board on a Wave
« Reply #21 on: May 23, 2017, 03:36:35 PM »
You need to pump sideways, ie left right left on and on, just like on a skateboard. The wiggle transfers power to the fins and they act like a fish getting power from its tail. On a  thruster, you are pivoting on the side fin and getting thrust from the tail fin. That's why thrusters have  drive.

PonoBill

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Re: Speed of a Board on a Wave
« Reply #22 on: May 23, 2017, 04:04:18 PM »
The arguments are not whether or not moving up and down the wave increases speed, but rather what the mechanism is. You're not gaining speed because you are going to the top of the wave and sliding back down again. You exchange Kinetic energy for potential energy as you climb the face, and then exchange potential energy for kinetic energy sliding back down losing lots of energy in the process due to friction.  And it's a dinky amount of energy to begin with.

Digger, water doesn't move up the face of a wave, it's fundamentally stationary, it just looks and feels like it's moving. Wave energy is what is moving. Just like shaking a rope up and down, the energy travels down the rope, the rope just moves up and down.

The increase in speed is because you change the angle of the board across the wave. If you could maintain the greater angle you would continue to accelerate (rapidly) until you reached the speed associated with the angle. Look at the video above in terms of the angle of the board across the wave. Lights should go on.  If you could hold an angle of 89.999 degrees to the wave you'd very quickly be traveling at 1,145,900 MPH, assuming a 20 mph wave (and the acceleration would turn you into a slightly lumpy liquid). The pumping that you believe is driving all this is at best 50 watts of power--and that's a ridiculous over-estimate. The shove you feel in your legs and the subsequent unwinding is acceleration/deceleration, from energy being transferred from the wave to the board and rider.

Tom--drive from a fin is a fictional force at best.

We can't hold a very extreme angle to the wave for long, friction overcomes the amount of energy being transferred and the wave slides under you. So the rider pumps--going from an unsustainable angle and related acceleration to a sustainable one. 

Curse you Beasho. You sucked me into this thread. I give, YOU teach them math and physics.
« Last Edit: May 23, 2017, 04:12:54 PM by PonoBill »
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mrbig

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Re: Speed of a Board on a Wave
« Reply #23 on: May 23, 2017, 04:44:19 PM »
What happens when you try to sink something that would rather float? It speeds up..

Repeat at your convenience. As an ex short board contest groveler no pump no speed no moves no advance. BIGGER boards the effect is more subtle cuz it's harder to SINK the aircraft carriers we ride..

Oh yeah, when you are taking off on a short board whaddya do? Sink it hodad!! Why? Cuz it pops out! Oh, how strange..
« Last Edit: May 23, 2017, 05:00:39 PM by mrbig »
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digger71

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Re: Speed of a Board on a Wave
« Reply #24 on: May 23, 2017, 04:52:41 PM »
Digger, water doesn't move up the face of a wave, it's fundamentally stationary, it just looks and feels like it's moving. Wave energy is what is moving. Just like shaking a rope up and down, the energy travels down the rope, the rope just moves up and down.

I'll have to review my high school physics, but was always my understanding that water moved in a circular pattern as the wave passed under it.  Eventually the individual water molecules wind up back in the same place, but only after completing a fairly large circle.  Up & Forward (the part we are talking about) followed by down & back.  And that's without the wave breaking

Tom

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Re: Speed of a Board on a Wave
« Reply #25 on: May 23, 2017, 05:03:21 PM »
Bill, how is the   energy in the   wave transferred   to   the   board?  I   could   never   figure   that   out . If the wave   energy  pushed  the  board ,  the faster   board  would  be  the  one  that  had  more  area  sunk  into  the  wave, but  that  doesn't  make  sense .

ps, back  to  drive.How come a fast  Skip  Fry   board   in perfect  trim can be past  by an inefficiently  shaped  board by a pro surfer  that is pumping   down  the  line ?

LaPerouseBay

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Re: Speed of a Board on a Wave
« Reply #26 on: May 23, 2017, 05:08:13 PM »
/
I'll have to review my high school physics, but was always my understanding that water moved in a circular pattern as the wave passed under it.  Eventually the individual water molecules wind up back in the same place, but only after completing a fairly large circle.  Up & Forward (the part we are talking about) followed by down & back.  And that's without the wave breaking


zing!  particle in a wind driven wave.  My kinda particle.



Downwind paddle surfers on either SUPs, canoes or skis can attain peak speeds of around 18mph so not as fast as Mavs but faster than most surf spots.   LaPerouse Bay keeps good records of his ski runs and I'm sure he's hit the red line a few times... but I guess that isn't a board.  But I've had an 18 mph spike before.  The rudder couldn't handle the speed and I crashed hard.
/

16 is my record in a ski.  It was a big drop.  You were on your standup, we had been chatting a bit, then we "engaged" the reef.  The water changed color and I had to step on the gas.  I get spooked when the water color changes in there.. :)


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mrbig

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Re: Speed of a Board on a Wave
« Reply #27 on: May 23, 2017, 05:21:14 PM »
Amazing pic!
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Beasho

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Re: Speed of a Board on a Wave
« Reply #28 on: May 23, 2017, 05:29:14 PM »
Awesome!  It's like dancing through a bar fight.

digger71

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Re: Speed of a Board on a Wave
« Reply #29 on: May 23, 2017, 05:40:05 PM »
Awesome!  It's like dancing through a bar fight.

Classic description Beasho!  One wrong move and you're part of it

 


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