Flex Measurement

General Discussion
61

KC, that’s not OT at all. Thanks for quantifying those forces. Some of us are

almost on speaking terms with math but need guys like you to come in and clean

up every now and then.

My riders that fall out of the sky regularly tell me about the different kind of landings

that they look for and what you describe(landing flat) fits into the ‘‘stupid’’ category.

(actual conversation—me: ‘‘what kind of landing did you do when you buckled this board?’’

pro: ''Oh, it was STUPID!!") Usually they look for soft spots but sometimes they’ve got to

try something different and those big air-drop floaters that you want to land tail-first

don’t always go as planned,etc.

The forces and dynamics involved make breaking some boards inevitable.

Mike

62

How about ‘slight digression’ rather than OT, sort of like this little ditty, which starts off with that ‘Huh, what the hell is this about?’ kind’a feeling, but brings in home in the end.

How fast was the surfer going when he/she left the wave to rise one meter above it?

Given the conservative nature of a gravitation field, again neglecting air resistance, this result can be quickly estimated, in fact for a surfer and surfboard – they would have to be traveling at about 16.0 km/hr or 9.91 mi/hr. Not exactly ‘ripping’ speeds, huh? I guess skill counts.

The curious thing here is that the weight of the surfer/surfboard drops out of this calculation. That is, if a 230 lb person on a 10 foot 25 lb SUP can get that kind of speed they too could travel the same vertical distance – assuming air resistance could be neglected, and for relatively small distances it often can. This sort of begs the question then, that is, why you don’t see all that many ‘airs’, even if they’re not a full meter high, by surfers riding 10 footers?

Here’s my shot at an answer.

Longboarders could achieve such speeds, but on waves in the head-high or less category, you can’t really get the required acceleration on longboards to get you to that velocity in sufficient time – remember, it all has to be oriented in the correct direction. You may be able to pull it off, if the face was long enough so you could ‘ramp’ up your speed. In fact, that happens a lot –i.e. it’s not uncommon for longboarders to be traveling fast enough to achieve a little take off as they come off and over the shoulder. But to pull off that kind of acceleration in a sufficiently tight space requires another kind of beast –e.g. a shortboard.

I don’t think it’s appropriate here to discuss it, but again I’m taken back to the notion that it’s not really all about speed, but more about acceleration, in surfboard design. This is particularly true in shortboard design, which, to a very high degree, tends to be about improving acceleration, which is often what is being referred to when terms like ‘responsive’ are used.

But back on topic, where there’s acceleration, there’s force, or stress if you like, and where there is stress, there is deformation – so, where back on ‘flex.’

kc

Note: The cartoon is completely OT.

63

Hi Kevin,

Yes, weight is often negligible. You can see that clearly by the weighting in the equations when small distances come into play. A two meter drop has a variance in typical human weight and surfboard weights that allows for a maximum speed variance of about 20% tops. And that’s really pushing it (difference between a big guy on a big heavy board and a small guys on a small light board). Momentum and drag seem to have a funny relationship :slight_smile:

I reckon the ramp factor is a major part, but skill level and board design are probably big factors too.

Have you watched a surf flick called LOG? You need to :wink:

64

Never saw LOG but I just read some reviews and a description of it.

Forgive me, I don’t watch a whole lot of video, none actually, other than the free stuff on the Net, and not that much of that either. Also, I’m no longer plugged into the local surf ‘Culture’, so I generally miss a lot of this kind of stuff. (Apparently, I don’t play well with others?)

As for LOG, wow, I stand corrected, obviously somebody figured it out. But I still do stand by my comments that it’s more about acceleration than speed, and modern longboard design has moved in that direction.

Looks like a nice video.

kc

65

No worries Kevin.

I guess you’ll appreciate that progressive longboard designs are oriented around being light, maneuverable and fast :smiley:

I’ll try to dig up a LOG clip for you.