Haavard,
Without knowing the precise details of the construction, it’s difficult to make any remark on…oh wait! they said it’s patented, so the details should be on Google Patents. When I have time, I will look at it.
Funny, my students just took their midterm on pressure vessels. Here’s the midterm solution:
http://maecourses.ucsd.edu/mae131b/Midterm1_2.JPG
Here’s a crash course simplification for a surfboard application:
- slice the board longitudinally, to get a stringer-like cross-section
2)take the greatest thickness of board: d=2.5"
3)take the thickness of the laminate(only the glass and resin, ignore high density foam): t=.03"
4)take the pressure: P=6psi
5)longitudinal stress at thickest point of stringer=Pd/(2t)=62.5/.06=250psi (this is an upper bound)
So lets assume the pump adds 250psi stress to the laminate. That’s kinda impressive considering 6psi is only about 40% more than atmospheric pressure(1atm=14psi (6/14=.4)…you couldn’t drive a car or ride a bike with tires that have only 6psi in them. Laminates break at around about 50,000psi. While you are riding the board, laminates are probably regularly experiencing 10,000psi in stress. I’m spittin this out, so if there is a mistake somewhere, please let me know.
The 250 psi is tensile…when you tighten a guitar string, what happens? The pitch gets higher…higher natural frequency. You can actually see this with a rubber band. The more tension, the faster it vibrates. So adding tension will make the board recoil faster. Will it also bend less? No! The rocker deflection should be the same at any pressure level. Can’t think of an at home demonstration for that one. This a dynamic stability problem–the calcs are heavy.
This whole rant is a drastic simplification, but assuming the entire surfboard is a pressure vessel and that pressure is diffused evenly in and out of foam cells, the following statements should somewhat accurately describe the board’s behavior:
1)The board doesn’t have adjustable flex
2)The board has adustable recoil rate
3)The adjustment of recoil rate could not be changed by more than 5%…probably closer to 1%
I’m not bashing or endorsing. I have a lot of respect for anybody who is doing something new and creative.
How can I demo a board in San Diego?