Last time I tried to post Larry's speed document it got all jumbled. This time I am just posting links to Part 1 and Part 2.

http://www.rodndtube.com/surf/info/SurferSpd/SurferSpeed_vs_WaveSpd_Pt1.pdf

http://www.rodndtube.com/surf/info/SurferSpd/SurferSpeed_vs_WaveSpd_Pt2.pdf

For those like me whose brain hurts when I see formula, you'll need to take precuations.

Bob

so if Vmax for a 25 foot wave, crest to trough, is 35 mph, this rather puts the kibosh on a certain ranter who, with his GPS-enabled buddies, were posting egregious speeds here a year or so ago. The ranter was banned... the GPS posters maybe oughta been to. If you believe LG

Here is Larry's conclusions.

"Let’s try some examples:

For a 2-meter (true height) breaking wave, how fast could a surfer go on a fast section?

Vsurfer,km/hr = 20.40513366* SQUAREROOT (2) = 28.85721676 Km/hr

For a 3-meter wave, Vsurfer, km/hr = 20.40513366*SQRT(3) = 35.34272823

For a 4-meter wave, Vsurfer, km/hr = 20.40513366*SQRT(4) = 40.81026732"

The links in the first post (above) contains the calculations used to generate these examples..

Bob

wheres roy?cheers huie

now retired

Here are some numbers for the superbank here in australia.

Distance from the take off at Snapper rocks to the end of the rocky groyne at Kirra is 1.2 kilometres, in 2004 surfers were getting rides this long.

Average of the peel angle about 40 degrees.

The time it takes for a line of swell to get from Snapper to the Kirra groyne is 2 minutes.

Speed is distance times time which works out that the wave peeled at a speed of 36 kilometres per hour or 10 metres per second.

Doing a bit of geometry you can work out that the swell was travelling at 24 kilometres per hour, which means that a surfer trimming ahead of the curl is travelling at a speed of 12 kilometres per hour on a swell travelling at 24 kilometres per hour.

Question 1: How do you define the swell line? Is it a line paralleling the alignment of the crest of the wave (which seems to be the case)? Or is it a line perpendicular to to the alignment of the crest of the wave (i.e. the direction of movement of the wave fronts toward shore)?

Question 2: Your comment about a decreasing peel angle being associated with a increasing speed, and vice-versa, is contrary to Larry's discussion that says an increasing peel angle results in increasing speed, and vice-versa. Which claim is correct? Or (as I suspect) is your 'peel angle' the complement of Larry's 'peel angle' and we have a conflict of definitions of 'peel angle'?

Question 3: You wrote:

I agree that the wave 'peeled' at a speed of 10 m/sec, assuming that by 'peeled' as used here means the motion of the point at which the curl breaks moves at a speed of 10 m/sec, or 36 km/hr (in a fixed coordinate system). But I don't understand how you obtained the values of 12 and 24 km/hr for the wave and curl speeds. Also I can't figure out how you can satisfy the Pythagorean Theorem with these numbers:

(12)^2 + (24)^2 = 144 + 576 = 720

sq_root (720) = 26.8 kilometers/hour, not 36 km/hr

Could you please provide a little more detail on how you obtained the values you presented?

FWIW, the speeds that I obtained are:

Speed of the surfer and of the motion of the break point of the curl (since they move together) = 10.0 m/sec

Speed of the advance of the wave crests towards shore: 7.66 m/sec

Speed of the motion of the breaking point along the wave crest: 6.43 m/sec

Note 1. These values could change a bit pending on the correct definition of 'peel angle'.

Note 2. The Pythagorean Theorem is satisfied for the speeds I obtained.

Thanks.

mtb

In the early to mid 1960's, Bob Shepard was riding a pintail balsa gun, on the North Shore, that he had made. The board was fitted with a boat speedometer that used a pitot tube pickup, at the base leading edge of the fin. Many of us thought we were going close to 45 mph, on 15 foot Sunset, and 20 foot Waimea. But Bob was reporting 24/25 mph on the drop at Sunset, and 27/28 mph on the drop at Waimea. We sure thought we were going faster. Just shows that you can't always trust your senses. The boards in use at that time were typically 10 to 11 feet long, and in my case 10' 5'' x 38 1/2 pounds. Those big paddle in guns would really move, when driven by a significant wave. Point is, we are going slower than we think we are.

Bill ThrailkillSHAPER SINCE 1958Thanks for the info on the speeds Bob Shepard measured when riding large waves. In the early 70's, the Omni board (Surfer Mag,V11,#6) used the same method (or an equivalent approach) to measure speeds obtained on smaller waves. I don't remember the details of the speeds obtained, but my recollection is that they were in the teens to low 20's.

These methods measure the speed of the board "through the water". Some other methods (e.g. gps) measure the peak speed "over the bottom". The speeds obtained with the two approaches are not always the same (for example when dropping into a wave, the speeds measured with the pitot set-up include the vertical component of speed, while the GPS measurements do not).

Over time, I've made over 70 measurements of peak speeds attained during a ride at several locations (primarily Swamis) with a GPS and riding waves ranging from a few feet to double overhead+. The median speed of the set of results was a speed of 19.7 mph and a mean speed of 20.4 mph. The standard deviation was 3.3 mph. The four fastest speeds recorded were 27.6, 27.9, 28.0, and 31.0 mph (by a kneeboarder, bodyboarder, surfer on a short gun, and a bodyboarder, respectively). Two of these speeds were recorded at the Wedge (bodyboarder, 15+ ft peak, 1.5X overhead), the other two at Swamis. The three slowest speeds were by a bodyboarder, a board surfer, and a kneeboarder at 14.5, 15.2, and 16.1 mph, respectively.

I decided to move this up, as it relates to several recent posts. I'm sure there is more sensitive instrumentation available today. Perhaps a digital speedo' with memory. Waterproof of course, would be in order.

Bill ThrailkillSHAPER SINCE 1958I'm with Bill T on this one just based on personal experience, not based on ever trying to measure anything. But, when I was younger I used to waterski, sometimes at a decent clip (35+ mph). Having surfed a fair number of waves, I have never felt that water-hardening-underfoot sensation on a surfboard that you get when going that speed on a waterski. Maybe that's just the thinness of the ski versus the surfboard? But also having fallen behind a boat at that speed, the sensation is not much like I've ever had falling off a surfboard (even on bigger waves). Off a surfboard you tend to skip once? Skiing you skip across the water a lot more. Check out this video -- a number of guys bounce 3, 4 times before they penetrate, and that's on a slalom course (not speed skiiing).

http://www.youtube.com/watch?v=YVA5W7mdGSc&feature=related

It just seems to me if anyone was ever doing 50+ mph on a surfboard, when they fell they would skip more like 8 or 9 times?

As for how fast CAN you go on a surfboard? Well, on a tow-in board, as fast as the craft pulling you, and then some if you crack the whip. On lots of jetskis thats at least 65 mph, and from what I read there is at least one that has hit 90+ mph. If you were so inclined, you could get pulled into a wave at somewhere around 100 mph, I'd reckon.

Who wants to go first? maybe before the 100 foot wave, we'll see the 100 mph tow-in? You would need one HECK of a glassy day!

Here's a video of a guy waterskiing 156 mph, if you think getting pulled that fast over water is impossible?

http://www.youtube.com/watch?v=R-el1H3PUG0

And a woman BAREFOOT water skiiing 100 mph (neck brace seems to be a good idea!)

http://www.youtube.com/watch?v=fn0aiYi8al4&NR=1

Howzit Keith, Back in my youg days when I waterskied I was in to speed sking and topped out at 95 MPH since my brother and his brother in law built speed monster inboards that would go over 100MPH. I fell more than once and I remember sliding along the top of the water and just dreading when I would slow down and catch a part of my body or any other part and then start tumbling till I would finally stop but I usually went about 100-200 ft before that would happen. But in the end that didn't even come near to the great feeling of surfing. Aloha,Kokua

Aloha, Kokua

## Pages