Anyone familiar with the concept of hull speed?
I think I decoded the Ambrosian message…who cares!
RS,
Based on your calculations … I can go about 70mph on my 6’2" twin. With all that drag on your log…and I do mean log…my little bar of soap would slide by ya no problem. So I say 7075 mph…nah…and thats on gulf shorebreak…(tongue planted firmly in cheek)…peace and waves…
Sean W.
Oceans23,
Three weeks ago a rode my fish on what might be my smallest wave ever that still might be consided hollow. Difficult to say because I was looking at its top jamming down the beach and laughing my head off. Based on the tangent of the cosine of the suns angle to the moon with Gemini passing through Libra. My calculated speed was 76.3604 miles per hour! Sorry to crush your bubble, brother. Mike
Rooster,
I knew it…that template was flawed(probably on purpose…lol) so you could get that extra mph or so…damn fins slowing me down…LMAO…looking for a new bubble…peace and waves…
sabs pointed out the important fact that speed through/over the water (TTW) can be different from speed over the bottom (OTB). For hydrodynamic calculations, it is the former that is relevant; for “making” the wave, it is the latter that is relevant. It’s not too difficult to think of some (transient) situations in which the difference between the two speeds could be on the order of the speed of progression of the wave toward shore, and perhaps in a few situations the difference might even approach twice that speed.
Bug_Power outlined a method for estimating speeds using a video recordings and suggested that the camera should be pointing directly at the surfer, and that fixed markings on the board (or the board itself) could be used as a reference length. Just to make sure that there’s no ambiguity here, it should be pointed out that “directly at the surfer” should be interpreted to mean that the line of sight from the video camera to the surfer should be perpendicular to the surfer’s path OTB, not perpendicular to the wave front.
From studies using overhead imagery, it has been determined that the angle between the alignment of the wave front/crest and the OTB path of a surfer racing across the face of a wave ranges from about 30 degrees (closer to 33) to 45 degrees (the latter probably being associated with large waves). That means that the maximum speed of the surfer OTB will be roughly 1.8 (33 deg) to 2.0 (30 deg) times that of the rate of progression of the wave toward shore.
The speed of progression of a shallowwater wave OTB is related to the water depth and the height of the wave. Van Dorn ("Oceanography and Seamanship. Dodd, Mead & Co. NY. 1st ed., 1974) gives the approximate speed/depth/height relationship for a sloping bottom (not necessarily applicable to areas where the depth changes extremely rapidly) as:
C(ft/sec) ~ squareroot(32.2 x (0.75H + h))
where: H = wave height (ft) (trough to crest), h = water depth. A typical breaker height (H) to depth of the water (h) ratio for a sloping bottom ranges from about 0.8 to 1.2. Hence for a 4 ft breaker, and assuming a ratio of 1.0, the speed of progression toward shore would be about 15 ft/sec, or slightly over 10 mph. Twice that would yield a speed of the surfer OTB of about 30 ft/sec, or about 20.5 mph–in the same ballpark as the other numbers being reported in this thread.
An 8’ wave would yield an estimate of almost 29 mph for a path angle of 30 degrees. But the path angle of the surfer would probably be somewhere closer to 45 degrees, so the actual speed OTB would be somewhat less than this. For example, a numerical simulation model of a surfboard on an 8 ft wave predicts that the maximum speed will be about 22.7 mph when the board is trimmed for maximum speed (predicted by the model to be where the wave face slope angle is about 47 degrees, and the board has an angleofattack of about 11 degrees) This results in a path angle of about 50 degrees – an estimate that is a bit on the high side compared with observation, but at least in the same ballpark as the range of measured path angles.
For the steadystate condition where a surfer is in the pocket of the wave, trimmed for maximum speed, and progressing across the face of the wave at exactly the same speed as the progression of the lip along the crest, it is difficult to achieve any significant speed improvements over a decently designed board by an increase in hydrodynamic efficiency. As discussed above, the surfer’s path over the bottom is a diagonal one, and to maintain his position on the wave, the component of his velocity (OTB) towards shore must match that of the wave. Hence any speed increase will be in the component of his velocity that parallels the wave face/crest, resulting in a reduction in the surfer’s path angle OTB.
The surfer’s speed is determined not only by the hydrodynamic efficiency (lift/drag ratio) of his craft, but also by the magnitude of the propulsive force. The latter varies with steepness of the slope of the face of the wave. There are four angles that play a role in determining his speed: (1) the slope of the wave face at the position of the board on the face of the wave, theta_w, (2) the slope of the wave face along the path of the surfer, theta_L, (3) the slope of the wave face in a plane perpendicular to his path, theta_t, and the path angle of the surfer OTB (theta_p, discussed above).
It is the magnitude of the slope angle along the path of the surfer that propels the surfer. Its magnitude is related to the slope of the waveface at the location of the board, and to the path angle of the surfer, by the equation:
tan(theta_L) = tan(theta_w) x sin(theta_p)
The faster the surfer goes, the smaller theta_p becomes, resulting in a reduction in the slope along the path of the surfer, and a reduction in the propelling force. Thus an increase in hydrodynamic efficiency is offset, to a considerable degree, by an accompanying decrease in the propelling force. The situation is analogous to a skier on a ski slope. If he heads straight down the slope, the slope along his path is steep and he gets maximum speed; if he heads diagonally across the slope, the slope along his path is reduced, and he goes slower. In he case of a surfer, the difference is that unless he goes on the diagonal path, he soon runs out of “hill” (wave).
In principle, one can increase his speed by positioning his board higher on the face of the wave, where the wave face slope is greater. Apart from geometric considerations (a head buried in the lip overhead creates considerable drag), doing so tends to decrease the hydrodoynamic efficiency of the board–primarily by making the wetted area of the bottom narrower, reducing the aspect ratio of the hull, thereby reducing the lift coefficient (per unit angle of attack), and increasing the induced drag. Hence when positioning the board higher on the face of the wave, the initial effect is a gain in propelling force with only a small reduction in hydrodynamic efficiency. However, if continued, at some point, moving any higher results in a reduction in hydrodynamic efficiency that more than offsets any gain in propelling force. Observations of pictures of surfers in trim on critical waves suggests that the optimum position is where the wave face slope is about 45 degrees (and in the model simulations mentioned above, the predicted optimal position was at a wave face slope angle about 47 degrees).
Assuming that the surfer on a typical state of the art board can travel twice as fast as the rate of progression of the wave toward shore (path angle = 30 degrees), a surfer traveling three times that fast would have a path angle of about 9.6 degrees. The driving force for the surfer on the typical board with a path angle of 30 degrees is about onehalf the driving force compared with if he went straight off. For a surfer and board going three times faster, the driving force would be reduced to about onesixth the force if he were going straight off, or about onehalf that of the surfer on our “typical” board with a path angle of 30 degrees.
Simulations (with a simpler model than mentioned above) suggest that about 60 percent of the drag of surfer on a typical board on a 4 ft wave is induced drag, with the remainder associated with skin friction drag, form drag, and finassociated drag. As speed increases, one would expect the induced drag to remain approximately the same in magnitude (although less as a percentage of the total), while the remaining sources of drag would increase roughly as the square of the speed. Hence if the typical board were to travel three times faster than normal, the total drag would increase by approximately a factor of 4.2. Combined with the reduction in propelling force accompanying this increase in speed, this means that the hydrodynamic efficiency (lift/drag ratio) of the typical board would have to be increased by a factor of 8 to 9 to achieve a factor of 3 increase in speed. This would be a truly remarkable achievement.
MTB,
What are you so angry about? There was no call for that. Take deep breaths. Relax. Count to ten. Feel any better?
That was great. I understood every bit of it, too. Mike
I’m not an expert in this stuff, it’s not my field, I’ve never studied it formally, and I’m just a hobbyist board builder. I don’t have access to models, film footage or any of that either. But I am interested in learning.
I was just wondering if, as with boats, the length of the waterline wouldn’t affect maximum speed. (would a 20 foot surfboard have a theoretically higher maximum speed than a 10 foot board?)
when you say “For example, a numerical simulation model of a surfboard on an 8 ft wave predicts that the maximum speed will be about 22.7 mph when the board is trimmed for maximum speed” – what would that model predict if the surfboard was 25 feet long?
DAMN! I’m only 186,00 miles per second. You barely edged me ambrose damn you
Aloha
Bryan
as I read the various inclusions in this thread I reflected on my oppertunity to measure my speed on a particular wave… my study on my home made electro encephlograph reading of my photographic memory…and came up with the figure of 187,000 miles per second . which is at the threshold of the speed of light and that my friends settles the question of who may be the fastest human in the history of mankind…I would like to thank Kevin Breedlove for Inspiring me in that weekly reader article and thanks to the sun for going down to remind me of the difference between day and night… ambrose…cool crescent moon,what a planet we live on aint it great and exactly the oldest un answered un measureable topic in our adolescent sub culture…no I wasn’t riding my mat and I think I saw a mat pass me up…dont look into the laser when you go past the inside time gate Dora is aiming it at everybody’s eyes
Regarding the use of GPS in surfing, I was given permission to post the following:
GPS test pilot, James Sowell:

Former pro bodyboarder/competitor in the 1984 Morey Pipe Championships

Regarded as one of the fastest bodyboarders

Contributing editor to ROT Magazine

Recent surf mat convert
The setup you are looking to use is a Geko GPS made by Garmin. Combine this with an Aaquapak and you have a truly waterproof GPS. There is also a watchsized water proof GPS.
I first started using the GPS on a boogie, in winter swells, some up to double overhead, normal beachbreak waves also, used in medium wedge 815 foot faces. Haven’t used more then a dozen times to get a feel for it. 1213 mph is on plane, 1518 mph is a typical tube speed. I made a really nice tube, and only peaked at 14 mph.
Most waves are sub20 mph. You can boost it up a little bit by pumping down the line and suddenly dropping to the flats, I hit 21+ mph using the drop technique. These same waves, without the drop, would be 18 mph. Wedge (the Newport, CA Wedge) yielded some of the highest speeds at 23 mph. Again large drops at 18 mph got me a good full body air after a sidewave wedge through main peak to launching ramp.
On my surf mat, the highest Wedge speeds were also matched on small mushy reforms of only 13 foot at Huntington Beach, that had little foam balls occasionally breaking on mostly clean unbreaking walls. As I finally connected into the shorebreak, I set up a backdoor on a small foam spot, maybe 2030 yards ahead of me… the mat was hustling pretty good at that point, at 23 mph.
Depending on if you are with, or against the grain of the swell, the speeds against the water (hull speed/air speed) seem to add or subtract to the effect of perceived speed, but under most situations, the actual speed was not
observed to change that much.
I will need to experiment more with this. I got a pretty good perception of what was what, and eventually could call
it within 2 mph after the wave, i.e. how fast I was going before I looked at my GPS.
I feel that 27 mph is pretty darn fast, but I won’t say its impossible. It
s very hard to beat the speed of a surf mat or a Wedge wave, especially when the sidewave connects you, getting a lot more push than normal.
None of the waves I rode were were really fast waves (except for Wedge) that I have tested on. When I hook up a good day at a racetrack type of wave with a lot of juice, I will
get a better idea of the upper limits on speed.
I have hit higher speeds, maybe by only a little bit on a surf mat, at good point and reefbreaks, but did not have the GPS on at the time.
Soul (James Sowell)
Couple of years ago I had an 11footer made for me. The thing felt like it was going 100mph but alas it was all in my mind after watching a vid of the waves. Could it be the difference in the way one board has a smooth glide effortly trimming on a wave covering flat sections with the minimal effort and another shorter board you pump like a bugger to get it down the line past closeout sections. Different boards, different waves. Both feel as fast to me but as long as I’m in the pocket I couldn’t care how fast I go. Last weekend i went so fast on me bonzer I start to go back in time and even dropped in on myself from the set before. which was nice.
Cheers Joe
For what it’s worth, I haven’t seen Roy’s boards or seen him surf. I am however willing to at least consider that the speeds he has estimated to have attained may very well be for real. Keep in mind that the length and design of his boards (and the fins on them) are far from anything most of us have seen or ridden. Those late model GPS devices are indeed impressive but fairly expensive. I find the potential speed attainable with a huge board to be intriguing.
Roy/john/all,
I’m also willing to consider claims. I’m just a skeptic of anyone’s claims that are illogical or counter intuitive to me. This includes the claims of many who are much more knowledgabe and skillful than me including Blakestah, Burt,Loehr, and others. I’ll believe it when I see good data by my own criteria. So far the photos I’ve seen of Roy’s show a great big beautiful longboard with unusual fin setup in small, average, fun lookin surf. My sarcasm isn’t to discredit. I’m no expert. I’m into having fun. This is all for fun. Isn’t it? Mike
I could care less what the number is… it’s just a number. But if you’re really going 3X the speed of a normal surfer, then lets see it… we don’t need another surfer for reference, we’ve all seen plenty of surf flics, if you’re going that much faster it’ll be obvious.
You can’t blame people for being sceptical when someone makes a substantial claim without proof… especially when done in a bragging maner.
…I’m still trying to figure out what a ‘mushy fast wave’ is too… seems a bit of an oxymoron.
Although I have no direct experience with Ray’s boards  Ive seen VERY similiar (at least from what I gather of his posts) boards and fins. The numbers dont seem to add up to me  unless Roy is doing something vastly different from everyone else and is so far ahead of the rest of the surfing world that I wouldnt be able to understand. Having shaped for awhile now, with an engineering degree, and having surfed all of my life  I am failing to understand his claims or how they can be possible.
I’m not disputing them, I’m just saying what rooster is saying pretty much.
Aloha
Bryan
John,
A Garmin ‘Gecko’ Gps sells for under US$200, and is actually the entry level unit. They are getting smaller and cheaper.
Roy
Hello Rooster,
The 3x the speed of a normal surfer claim wasn’t made by me, and I can’t claim it to be true. What happens around here a lot though, is that we get some very marginal waves which regular boards don’t have much success on. On a lot of these days shortboards and mals don’t even make it down the line far enough to make the first section, because the waves won’t allow it. I have designed my boards to take advantage of these sub par waves.
On a day when the mals and shortboards are getting buried in the first 20 feet, I could quite possibly be going 2 or more times as fast simply by sneaking around the corner into the next section, and then pulling in on the inside closeout section that is the only fast part of the wave and no one else is riding it.
Regards, Roy
Hi Bryan,
I think that 27mph is actually quite slow. It was mentioned on this thread that sprinters can run that fast, and if a mat has been recorded at 23, I don’t see why a specialized speed board can’t do 27.
Roy
Howzit MT,
There two speed producing factors which are not in your calculations, one is that muscular effort from the rider can propel the board, and the other is that lift can be gained from air rushing up the face of the wave, using the nose of the board. I am still wading through your analysis!
Regards, Roy
I think that 27mph is actually quite slow. It was mentioned on this thread that sprinters can run that fast, and if a mat has been recorded at 23, I don’t see why a specialized speed board can’t do 27.
Seems pretty fast to me, but in all honesty I don’t have a frame of reference on a surfboard… for a surfboard is one of the few vehicles that I ride that I haven’t gotten a speeding ticket on. I know it’s fairly fast for a wakeboard, a pretty slow for water skiis.
Sprinters, however, do not run that fast (not yet at least), and there’s but a handful of them in the world that can sustain over 20 for any measurable amount of time. I think the world records are comming in at 2223 mph… the scary thing is, the mile runners aren’t far behind in terms of speed, but they’re running 15 times the distance.