Hydrodynamics Part(s) I through IV

For those of you who have not come across this, I found this link to be pretty interesting, although it is

very dated. Enjoy!


dont know why the link didnt post…


Thanks for posting that, it’s a good reference work, even though the speed analysis is WAY out of date (surfers are going much faster than Terry has calculated, although to be fair Terry does state that it is very difficult to predict speed via calculation in advance, and the best method is to measure speed using an instrument )

My last 3 speed measurements have been 36.5 mph, 38.1 mph, and 36 mph, on waves from head high to 1.5 x overhead



Ahh, once again speed measurements rear their ugly head.

Terry posts here regularly, Tom Bloke. And he has constructed multiple methods for measuring his own speed on his own boards, and found them in sync with the article.

Bill Barnfield has also constructed his own speed measuring apparati and found measurements that largely agree with Terry’s.

And at least a half dozen others have made concerted efforts at measuring speeds and found measurements all in the same ballpark.

Strangely enough, they are all roughly half as fast as yours.

Now, what am I to think? Either TomBloke is right, and all these men of science and surfing design are all off, in exactly the same way, through multiple different techniques for measuring. Or the ones who got similar answers are right, and there is something fundamentally broken in TomBloke’s measurements?

No Blakestah, all those other guys are using similar equipment

Like it or not, my UNIQUE boards are approximately twice as fast

That’s just the way it is, I have a few design breakthroughs in terms of surfing speed, get used to it !

Having a respected name isn’t the same as going fast. . . life is full of surprises. . . . my boards are faster than Bill’s or Terry’s !!


can one of you tell me how i can enlarge the pages on the link. when i open them the print is too small to read, and i want to read them! please help.

hold down “CTRL” and hit “+”

this will increase the size of the text

brandon, you are sick.

38 mph? That’s as fast as I used to need to go to barefoot behind a boat. How much of the board is left in the water, just the last 2-4 inches or so?


hi Maxmercy,

Barefoot skiing is a slightly different scenario. … . more power, more drag per square inch of wetted surface area, and lift generated from a small surface at a high angle of attack.

On my board it is a case of less power, less drag per sq inch of wetted surface area, and lift generated from underwater foil and planing bottom at a lower angle of attack . . . thus more wetted surface area, but having said that, it’s tail riding and most of the board is out of the water at that speed. … .



You can also download the Firefox 2 browser. It’s free and

includes a function for enlarging text/images:



Terry posts here regularly, Tom Bloke.

Hi Blakestah, yes I am aware that Terry posts on Swaylock’s, and I have corresponded with him from time to time over the last few years on hydrodynamics.

Naturally I have great respect for Terry’s work, and have learnt a lot about lift from Terry and yourself, I thank you both very much for sharing your knowledge.

Reading Terry’s work, he states quite clearly that theoretical prediction of actual surfing speed is very difficult, and that actual measurement in the water is the way to go.

In your post you imply that either I am wrong or Bill Barnfield and Terry Hendricks are wrong. … . . that is not true, strictly speaking, and is unnecessarily adversarial. In fact, I am sure that the measurements done by Bill, Terry, and myself have a similar level of accuracy. . . we are all just reporting our findings, thus we are not arguing over whose measurement is correct, they are no doubt ALL reasonably accurate. . … . . the point is that my boards are faster !

It’s not a case of “men of science and board design” verus Tom Boke (as you put it) . . . we are ALL men of science and board design. . . i’m just scruffier and hairier than the others that’s all !


My last 3 speed measurements have been 36.5 mph, 38.1 mph, and 36 mph, on waves from head high to 1.5 x overhead

What waves are you surfing that require you to go that fast in a straight line? That’s faster than Laird is going at Jaws. Can you ride your board at Jaws?

Kendall my bet is that Laird is going much faster than 37mph at Jaws, but we don’t know because the last time I heard he couldn’t tell us ( I sent in the question to Laird about measuring speed when Surfermag interviewed him, the question was put to him, and he replied to the effect that he isn’t planning to measure how fast he is going)

As for asking what waves I am surfing which require me to go that fast, the waves don’t require it, they allow it, big difference, but it’s a strange question. . … … haven’t you ever surfed a break where there are sections breaking down the line and you race to beat them? The waves don’t have to be big or hard breaking to break fast down the line, but you already know that so why ask ?

Can I ride my board at Jaws ? . . . . of course I can make a board which will handle Jaws, and probably ride it there, I think most surfers could ride Jaws, it’s only a big sloping piece of water . . . I don’t think that riding it is an issue. . . it’s the wipeout. . . . I doubt if I would survive a wipeout !


Whenever this speed talk comes up it only takes a little while before someone starts saying like “who do you think you are saying that you go so fast do you think that you are better than Laird (or Bill, or Kelly, or . . . … ) ?” or words to that effect. Basically it’s an irrelevant question, it’s not a social issue I’m just reporting what I do.

Anyway shouldn’t we be talking about the Terry Hendricks thesis? . . . there’s some interesting material in there, so lets not hijack the thread please


No, the main issue here is reliability.

There is a general trend developed from the wave speed measurements of many other people. Not one other person, multiple people, and not one measurement technique, but multiple different ones.

It says surfers generally go roughly half as fast as your measurements on the sorts of wave sizes you’ve done your measuring on.

You’ve posted ample video of yourself surfing. In watching it, I have become convinced that your water speed is nothing substantially different from that of other surfers. Yet you say you are measuring your speeds at twice that of others.

I would urge you to calibrate your measurements. Try running with the device on. See how fast it says you can run 100 meters and whether that is twice as fast as Carl Lewis’ best.

We have already ( long ago) established that the maximum speed on a wave is related to the the maximum speed of the wave.

e.g. you cant surf 100 mph on a 10 MPH wave.

At 100 MPH for 60 secs you would surely be in another County? Or Country?

Or wheres the fun in attaining 100 mph momentarily ?

Modern surfing is not a " LINEAR ( straight line) speed" - focused sport,(Like swimming ), unless youre on a mal andf surf like an old man. Read an article “The men who go straight.”

BUT (since the 70’s) we have needed to “cut-back” to catch up to the the wave, so the board is now faster than the wave.

So whats the big hype about speed, and in what direction and for what duration ?

I thought it was about manouverability…Or is Slater wasting his time…


Wow, at fisrt I wasn’t gonna post the link to the Hyrdrodynamic Info, because I thought most people would consider it

useless! I’m glad I did, it sure sparked some solid meat and potatos conversation.

So exactally how do you take a speed measurement on a wave? distance x time traveled between two landmarks?

And how fast are guys really goin at Jaws… or Teahpoo, Mav’s or Waimea?


Are you guys talking speed through the water or speed over the ground??


A minor correction, if you please. Surfers have been outrunning the wave, and having to cut back, since the 1940’s at least. And most likely before that. The improved maneuverability of the equipment has made it happen faster, and enabled more people to accomplish the maneuver, without disaster.

RIKDS has a good question: Are we discussing speed over the water, or speed measured over the ground under the water?

I remember a quote regarding Teahpoo saying the speed over the water is relatively fast, but if you look at the surfer from the beach, he isn’t really covering much ground. The water is sucking up really fast, kind of like one of those waverider contraptions that shoots water up a curved surface. The surfer is surfing “fast” but he isn’t going anywhere.

So what are we talking about here? MPH as a lobster sees you as he sits on the reef looking up, or MPH as a lazy anchovie sees you as he floats on the surface, watching you surf by?

I gotta know. Doug