kookaburrahz said...
i allways believed deep channels didnt help grip they just made the board more dragy (more slowing then hard edgeing) spoke to some fluid dynamics guru about it one day do you look at that sort of thing when designing your boards?
Hey Kookaburrahz,
Its definitely is something I put some thought into because it’s not just channels but also the rocker and concave and how rough the surface finish is on the board plus the outline all contribute to one or more parts of the different types of drag. And the impact of drag on performance, I find, is really noticeable in light conditions and also the top speed you can get out of your board.
I think you’re right that channels will increase drag if everything else about the board and the way you ride it remains the same. When you think about it a channel is like a very elongated fin and in the same way bigger fins create more drag so so channels. The reason though that’s its so hard to say that this is categorically true for a board is that the things that a fluid dynamics guy would come up may not take into account how things like drag and lift feed back into the way you ride the board which in turn changes the values of the drag and the lift and so on back and forth. This is in part why prototyping is such a critical part of board design and why there is so much art and to board design.
I’ve found with riding channeled boards with the channels concentrated in the middle section that I can use much smaller fins – less drag - and can ride the board flatter (less edge) and ridden this way the light wind performance and speed seemed on a par with similar boards I was try ( bear in mind it’s a small sample I’m drawing on).
However, there are a few other reasons in the pro’s and cons mix that I think channels add to the story: a good weight vs stiffness trade off, softening landings and better grip when you land without being able to get the rail in as hard as you like.
The weight vs stiffness is a really interesting one and one that Lars Molle at Naish talks about a lot in his pursuit of ever lighter and stronger boards. Based on some back of the envelop calcs, if you bend a piece of core material to create the channel and make the channel as deep as the material is thick then you roughly double the stiffness of it. You basically get this for free with no weight being added. It also has the added benefit that the stiffness from the laminate increases greatly too (to see this just take a playing card and bend it down the long axis and then try and bend it on the short axis which is nearly impossible). This is the same thing that concave does to stiffness.
An interesting side note on the science of design (not the material science part, just the design part) - I was talking to a mate in NZ whose involved in making world class carbon windsurfers and he told me about a Ph.D some guy in the US did on really detailed modelling and measurement in a lab setting for windsurfers. Great data, great engineering models but it went nowhere because it was impossible to translate the science into the feel in any meaningful way – again , for me at least, reiterates the importance of the art, craftsmanship and prototyping in building boards.
Sorry for the long post but this is an area that really fascinates me.
Cheers
matt
