Aloha!! I didn't think there would be any more responses to our spirited discussions on "Surfer Speed...etc". It seemed to have played out. Conclusion: it remains to be determined just how fast surfers CAN and DO actually go on surfable waves.
But more answers will be forthcoming as more 'speed' events are staged around the world, with GPS devices such as the "SBOX" doing the actual measurements of instantaneous speeds over the bottom. Unfortunately, those devices can be fooled by wild body gyrations if the measuring unit is mounted ON THE SURFER. And they can report anomylously high momentary speeds when they are mounted on the front of the board. Think bottom turns, or banging off the lip.
I suggested that the device would best be mounted on a surfer's lower leg, or implanted IN the surfboard, between the surfer's foot positions (which don't shift much on a short board). That's impractical, so I think the leg-mount idea is best.
But...if you want to measure the surfer's speed ACROSS THE WATER, you would need to ALSO know the speed of the wave itself over the bottom (at the point on the wave face where the surfer is riding at any given moment in time, which would need to be synchronized with the GPS speed recorded at the SAME TIME). I suppose that could be done with computers, but it sure is complicated!
The surfer's speed over the bottom is a combination of wave motion AND his motion over the moving wave form. His GPS speed is the vector sum of those two motions. If you want to know how fast he's moving over the surface of the water, you need to separate those two motions.
I think the most reliable and simplest way to determine the ACTUAL SPEED of the surfboard OVER THE WATER is to just use something like a boat speedometer, or even better, a pressure-measuring "pitot tube" on the bottom of the board somewhere below the position of the surfer. It wouldn't be able to give accurate readings when the board was tail-sliding, but would be fine when the board is trimmed for high speed across the fast-peeling wall of water.
You were interested in the likely maximum speed of the surfer on the wave in the video, which you called 'a 10-meter wave'. You can easily measure a small wave directly...just take a measuring stick out and actually measure it! But, when the waves get over 10-15 feet, it gets much more difficult...not to mention dangerous!
All you need to do in those situations, is to position yourself on the beach so that the the top of the wave just "touches" the horizon. Then, find a landmark up or down the beach that is the SAME DISTANCE from you as the breaking waves. Where the horizon intersects the landmark, THAT part of the landmark is at the SAME HEIGHT ABOVE SEA LEVEL as the wave crest, above sea level. This technique is called "The Line-of-Sight Method" of wave-height measurement. It can be accurate down to the nearest inch!
Note that this method can NOT tell you how low the water is, below sea level, in the TROUGH at the bottom of the entire wave. But that TOTAL HEIGHT, including the trough, is the TRUE WAVE HEIGHT. To actually measure the trough, you need somebody in the water just outside the impact zone (so he doesn't get slammed by the breaking wave) holding a long pole pointed straight up toward the sky. Then, with binoculars or, even better, a movie camera on the beach, you can observe (or record) how far the pole moves up and down with the passing wave forms.
The steeper the Slope of the bottom where the wave rises and breaks, the harder a wave can break, and the deeper the trough relative to the total wave height. For easy-breaking waves (think Waikiki), the trough might only be 14-17% of the total height of the breaking wave. For hard-breaking waves (think Pipeline), the trough might be 17-20% of the entire wave. For insanely hollow waves (think Teahupo'o, or "Chopo", in Tahiti). I don't know how deep the fearful 'Pit' is at that scary place, but it must be pretty impressive!
You need to know how big the total or TRUE wave height is, if you want to calculate how fast the wave is moving past the bottom. Then, if you can determine the Peel Angle, you can find the speed of the peeling curl relative to the bottom, or relative to the wave form's crest line. That was the main thrust of the essay on "Surfer Speed...etc."
My formula, rounded off to give an easily-remembered form, was:
Max surfer speed, MPH (or GPS Curl Speed, relative to the reef bottom) = 7 x SQUAREROOT(True Height, ft)
So, for a 4 ft wave, Max Speed = 14 MPH
and, for a 25 ft wave, Vmax = 35 MPH
Then for a true 10-meter wave (32.81 ft), Max Speed = 40.1 MPH
Remember, that wave may only look like about 8 meters to you, (or 26+ ft) without the trough.
Some of the biggest waves that Tow-In surfers have successfully ridden probably were closer to 20 METERS high (or 65.6 ft...looked like 50+ ft! Ask Ken Bradshaw: he rode of those Monsters on January 28th, 1998, on the North Shore of Oahu, Hawaii. It was the biggest swell since December 4th, 1969, when the North shore was closed out at 55 ft (Waimea Bay), and 60-70 ft off Kaena Point.
A 20-meter wave would break in about 84 feet of water (14 fathoms!), and would be moving at about 52 ft/sec, or 35.4 MPH. That's about 5 times as fast as you can paddle a surfboard. So, after the Yamaha WaveRunner tows you onto the wave, you make your drawn-out turn,... then...how fast do you need to go to make the wave?
If the peel angle is 45 degrees, you will need to go 1.414 times as fast as the wave propagation speed, or 50.1 MPH!
If the peel angle is 50 degrees, you will need to go 1.556 times as fast...that's freeway speed...55.1 MPH
My formula says you might be able to go as fast as 56.7 MPH. That's my Surfer Speed Limit. Probably not attainable in really big surf like that. We'll find out some day in the not-too-distant future. Who knows what the distant future holds for big-wave surfers? Rocket-powered boards that can FLY? Hmmm...
You may want to study the Winter Olympics Speed Skaters and their fastest body positions. Or practice standing on the top of a surf van going 55 on the freeway. I think you might get blown off by the wind...HA!
Thanks for your interest, Robert. Maybe "mtb" will weigh in, as well. That would be cool...
With the interest in the sport it seems odd that we haven't been able to do a direct measurement yet.
Thank you for the detailed answer; I knew that more rigorous minds than mine had been working on this question and it seems like I came to the right place!
Has anyone tried putting a radar reflector on a surfer? Maybe research-grade gps or laser range finding? I know there are some geologists on the islands with at least some of the right gear for it. I'm sure I sound naive asking, but one would think that there would have to be a way to do it.
The Laser Range-Finder devices would be too dangerous for the surfer, because of the possibility of blinding light hitting his eyes. Not worth the risk.
The Radar speed-measuring devices only would be able to measure the motion of the surfer TOWARD the device, (using Doppler). That would be useful information only if the device was set up way down the beach, positioned carefully, so that the surfer trimming in a straight line across the fastest part of the wave was heading DIRECTLY TOWARD the radar unit. That could work, I guess. Couldn't be THAT hard to do! I haven't heard of anybody trying it.
Just remember, tho', that the radar instrument would only be measuring the speed of the surfer relative to the fixed ground-based position of the radar unit. That is the same as the GPS measurements that the "SBOX" provides. So, both the radar unit and the SBOX can only measure the instantaneous speed of the surfer over the BOTTOM, not across the water.
The device needed to measure 'over the water' speed therefore needs to be mounted ON the surfboard, itself. But anything that you stick on the bottom of the board is going to cause at least a little extra drag. The pitot tube is less disruptive of water flow than a boat speedometer, but no matter what kind of hardware device you use, it will still need to be calibrated. Yikes! No wonder so few attempts have been made to date. We need new ideas! Anybody listening?
Thanks again for your interest, Robert! Maybe your questions will get some inventive minds focused on this interesting problem: If we want to know "How fast CAN a surfer go on a wave?", we need to figure out a way to determine: "How fast IS a surfer going across a wave?"
When I get back home, I think the Jeffreys Bay cntest is on. It might be worth contacting them as they tested the gps last year. I'll try to look into this. With the growing number of unversities offering surfing 'degrees' there must be someone interested in researching this. There are a couple in Oz.,
You may get some photos from a guy called Warren who just returned from the US and had a board made based on one of your designs. I asked him to include you in, when he sent photos.
I think I commented on this before, but I saw the Red Bull Mentawai show and they measured Mick Fanning at 42kph, by radar.
Then a few days ago I saw Storm Surfers on tv, with Tom Carroll and Ross Clark Jones. I think at fastest they measured was 60 plus kph, using a sensor that had GPS, accelerometer, etc.
You're right Larry about the position of the sensor. Imagine if you put it on the tip of the nose... there would be flashes of high speed. In the board between the feet would definitely be best.
these can be used with good results but they have to stay"line of sight" in other words if you put them in a back pack a run a dirtbike through the desert you'll get some insane,unbelievable numbers lol.
i have a very similar model that is not waterproof. aftermarket handlebar mounts are available the could be rigged to work in a leashplug or something if anyone is into it enough to try it. it's do-able. i've dabbled in waterski racing and boat racing and i'm also of the belief that we are not going nearly as fast as most would believe.
This is getting pretty interesting, once again! Anybody remember the famous "Cannonball Wipeout" at Waimea Bay, (back in the '60s, I think)? I can't remember the well-known big-wave surfer's name, but we all remember how he skipped down the face of a big one at the Bay, and got clobbered at the bottom of the wave, right in the impact zone.
Yeah, I guess the water skiers experience just how unyielding water can be when you hit it at high speed. Something few of us non-tow-in mere mortals ever get to experience first hand.
I still don't know how fast those guys on those 50 ft + waves are going when trimmed up high racing across the wall of water. It's gotta be pretty close to 50-55 MPH. If one of those giant waves dumps on you, you could find yourself suddenly immersed under 30-40 ft of turbulent water, maybe more, doing a 'deep dive' without having had time to equalize the pressure on your ears. Goodbye eardrums! Cold water in your inner ear could be very disorientating, not to mention extremely painful. Not good!
I wish we could SEE pictures of those surfers AND the wave they're riding, taken at the same moment their top speed was recorded. The speed by itself is interesting to know, but if we could get a reliable MEASURE of the wave height and the Peel Angle, we could then build a database of many such rides, from which we could determine the Maximum Makeable Peel Angle of waves of various sizes.
If a surfer's peak speed is measured by a radar gun or a GPS unit, that only gives what an airplane pilot calls "Ground Speed". It doesn't tell us how fast he's going across the water.
A pilot can refer to his Air Speed Indicator to see what his "Indicated Air Speed" is, which varies with altitude and outside air temperature...i.e., the air density at his altitude. Then, the instrument can adjust that IAS and display his True Air Speed. He needs to know his actual airspeed to maintain safe flight speeds (too slow, you might stall; too fast, you might rip the wings off).
Does anybody here in the forums, with experience in the boating world, have any suggestions for a tiny speed-measuring device that wouldn't add much Parasitic Drag to a surfboard hull? It would preferably be electronic, a digital device that could record or transmit the readings to a receiver on the beach. That's the ONLY way we are ever going to get reliable measurements of "True Water Speed" (TWS), like the TAS of an airplane.
By the way, if that "60 kilometers per hour" peak speed reading was measured by radar or GPS, then it was his "Ground Speed", i.e., speed over the bottom, and we can calculate the following equivalent Surfer Speed values:
Vm/s = Vkm/hr x 1000/3600 = 16 2/3 meters/sec
Vf/s = Vm/s / 0.3048 = 54.68066492 ft/sec
Vmph = Vf/s x 15/22 = 37.28227153 MPH
If we knew the true speed of his surfboard 'over the water', that is, True Water Speed, or "TWS", that is the same as the Curl Speed, "Vcurl", then we could easily calculate the Peel Angle of the Curl moving across the breaking wave crest.
So, if the peel angle is measured in degrees AWAY from the crest of the wave, then...
The Peel Angle, P = the Angle whose Tangent is the Square Root of the ratio: Vwave / Vcurl
Or, Peel Angle, P = the Angle whose Sine is the Square Root of the ratio: Vwave / Vsurfer
Note that: "Vcurl" is the true surfboard 'hull speed' over the Water, or True Water Speed.
and "Vsurfer" is the GPS or radar-measured 'ground speed' of the board over the Bottom.
In EITHER case, we need to KNOW the Wave Propagation Speed, "Vwave". But, in order to determine the wave speed, we need to measure either the True Breaking Wave Height, Hb, OR actually go out with a long pole and measure the depth of the water in the breaker zone.
All this was covered in my long-winded essay on "Surfer Speed Vs. Wave Height". My resulting formulas for Minimum Makeable Peel Angle suggested that the smallest angle was about 38.67 degrees away from the crest line.
Then, conversely, the Maximum Makeable Ride Angle, which I'll call the "Break Angle", i.e., measured in degrees away from 'going straight off', is about (90 degrees - 38.67 degrees) or, about 51.33 degrees. If it breaks across the crest any faster than that, he won't make it.
So, a surfer would only be able to get up to a GPS speed about 1.6 times as fast as the wave itself (or a hull speed over the water of about 1.25 times as fast as the wave) in order to attempt to make it across the faster parts of the wave. Any sections faster than that, and he won't make it very far. It will close out on him.
If that's the case, then the wave speed would be about 0.625 times his GPS speed, (or about 0.8 times his hull speed). From the wave speed, you could calculate the Water Depth, and from that, the True Wave Height.
If you use "Local Scale" for wave height estimates, you'll find that the true wave heights are about TWICE as high. In other words, a "Head High" wave is NOT "3", but actually is about 6 ft, INCLUDING THE TROUGH. Without the trough, it 'looks like' 5 feet, which is 60 inches, or about 3 "half-meters", the correct unit for Hawaiian Scale, (or "Local Scale"). Local Scale is about 3/5ths of what the wave 'looks like' without the trough, but is only 1/2 of the true Total Height.
'Nuff already! I'll clam up here...sorry, guys! I get carried away...
Thanks for all the comments and added information. Some day we'll know how fast we can go on a wave!
The key for me is the conversion of "good" speed to m/s (fps). So, if I get a 2 second tube I cover some 11m (35ft) @ 20km/h (5.5m/s or 18 fps). This fits reasonably well with my experience and also explains why that guy who was "miles away" nearly got run over.
I could be wrong, but from my grom days I remember Tommy Lee's cannonball wipeout on film. Waves at the time were cited as the biggest that could possibly be ridden. That horizion has certainly expanded
''m not sure if he is following the thread, but "Doc"knows about boats and technical stuff - I'll try to ask him.
to add to the confusion(lol), what we're not taking into account here is drag. all kinds of it. do 65 on the road and put your hand out the window. then picture your whole body experiencing this force. then there is my theory that almost all boards today ,so far are too wide to over come the drag devloped over 60mph.in the boating world guys who experiment with set up and different hulls find "walls" or speed barriers inherent to certain designs that cant by overcome easily or at all. these are all cuased by drag. then there is the human factor. take an experienced slalom skier who is used to diong between 30 and 40 mph. bump the speed up to 50. he'll freak out., hold on for a while and then notice it takes more leg power to do anything. . bump it up to 60. his eyes will pop out of his head! no amount of training at 50 will prepare you for over 60. it is not linear.that last 10 miles per hour will feel 2-3 times as fast. slalom skis have deep concave bottoms. no good at all for speed over what they were intended for. waaay to much drag. they also become uncontrolable which is why they are concave in the first place. consider the race ski. typically they are 7' long by 9" wide. if you watch a guy on a race ski his back leg is just a shock absorder and his front leg is almost locked out in front of him as for as he can keep it. why?drag. these ski have to be ridden over 50mph to over come the drag they create at lower speeds.over 50 they break free and stay on plane. from 60 to 120 they still have drag but what are yuh gonna do? they also have a 1/4"bevel from front to back on the bottom of the rails. the rear 2' of the ski has it on top as well for release. these skis are used in rough water sometimes so they are not lightweight. they are solid ,stout wood. probably 1 1/8 to 1 1/4 thick. the fins are very small compared to single fins of surf boards. they vary in size a little bit but basically 6" base by 2 3/4" tall and pretty rectangular. all the fin area that is required and no excess drag. so it is these thigns that make me wonder how wide tow boards are and if they will become narrower as great speeds are acheived....or if they will become narrower to acheive them in the first place.
fast forward to :20. these guys AVERAGE 115-125MPH. note the rooster tail coming off the back of their skis. it take 1200 horse power to do this. which brings to the limiting power when surfing but i digress,lol.
in other news it's pretty common knowledge among performance boats that pitot tubes tend to lie about speed by about 10% so the faster you go the more they lie. they tell you you are going faster than you really are which makes it depressing the first time someone gets aboard with a handheld gps. they can also go the other way due to hull conviguration and the way they disturb the water. i have seen the speed drop off on the gauge while under acceleration at around 80 coming up on 90 mph before,too.
im sure someone makes a transmitting type gps device even with a recall function but then your talking big bucks. even for the receiver units that are hardwired to a gauge in dash that aint exactly cheap. a company called gaffrig sells the industry standard and can be easily found. transmitting type? not so much.