In response to Pablo's recent comment on the subject of harmonic nodes in surfboards ( in blue )
This is a fascinating subject. Would you be willing to elaborate further on the relationship between harmonic nodes and board performance? Would you mind showing the location of the main nodes on the Olo of the Sun? Are you able to calculate with a fair amount of accuracy where they'd be located, prior to building the board?
Hello Pablo.
There is a primary node approximately in the centre of the board. This is convenient as it is also the designed position of the sweet spot not only in harmonic terms but also in hydrodynamic and control terms. The position of the node depends upon the position of the rider, it moves fore and aft with the rider, but only up to a point. If the rider moves too far from the sweet spot, the rider and the node of rotation part company. This happens also with swords. If Mr Pearce moves his grip from behind the guard down the grip towards the pommel the node on the blade will move further towards the tip. Also the 'sweetness of the sweet spot ' depends upon the width of the grip or in the case of the surfer the fore and aft width of the stance. A wide grip or stance means that there is a dampening effect. This happens because with a wide grip the pressure is inevitably spread into an area ahead of and behind the node of rotation where movement occurs. Thus with swords, one finds that a grip with both hands placed closer together gives a sweeter strike than one with the hands spaced far apart ( as one can do with some very long gripped swords ). Likewise with the surfboard, a narrow stance makes the board immeasurably more lively and responsive, and enables greater subtlety of communication between wave, surfboard, and rider to occur, and less dampening
Wider grips and stances allow greater leverage to be exerted, and this is useful at times, it's a coarser control setting, to be used when required. For the best response the stance and grip wil be made narrower when possible.
I'm of the opinion that useful harmonic nodes and frequencies are an inevitable result of the harmony in all aspects of board design which occurs when successfully pursuing functional design aims. Specifically, a riding position near the centre of the board ( which has general handling benefits ) a low thicknes to length ratio ( for low centre of gravity and flex) , and other aspects of board design e.g. rocker and planshape curve, when matched coherently, all have simple hydrodynamic and ergonomic advantages, as well as excellent harmonic properties. Without calculating the position of the node mathematically, it seems that the happy harmonic characteristics come hand in hand with matched foils and perfect geometrically generated curves.
It seems to me that the existence of nodes of rotation which will not move as energy transfered onto the board results in a harmonic vibration has tremendous implications, both whether the energy comes from the effort of the rider or the wave itself. A board thus finetuned would, for example, be magical in terms of absorbing energy from water irregularities--especially in big waves--without decreased performance , provided the rider stands at or near the node, right?--just as shock waves going through a sword upon striking would not affect the hand holding it at the blade's lower node of rotation.
Yes, that's quite right, and the feeling and results do indeed feel magical. Propelling the surfboard forwards via a weighting and unweighting motion transferred through the tail of the board into a dolphion tail motion is a well known phenomenon, but there is a vast realm of subtleties in the wave/board/rider interaction which can also occur. As the surfboard meets irregularities in the surface and the rider responds to the harmonic vibration which these interactions set up, there are gains in speed and control. This is the case even with the tiniest most imperceptible high frequency rider movements and the smallest of wave surface textures. The results include at times appearing to do little, but going far.
Regarding wave size, it is speed rather than wave height which has the most influence. Wave height and surfboard speed are somewhat related, but it is the speed which counts. As speed increases the harmonic response becomes crisper, more distinct, and more powerful.
The results are so remarkable that I've been wondering if by constantly communicating with the water in this way one can reduce friction by feeling water pressure on the board and adjusting it to keep it flowing smoothly, in much the same way that the fingers behave when paddling, but possibly with an added harmonic relationship between the frequency of vibration of the water molecules and that of the surfboard and rider.
Remarkable! This adds true depth of meaning to the expression "sweet spot". What a way to feel the wave!
PS.: I assume it would be nearly impossible for a harmonic resonance to ever develop.
Regards,
Pablo
All the best Pablo, it's great to hear from you, and I hope that you are enjoying your big wave season !
We'll see if we can get some video footage of the harmonics on the 19 foot Olo of the Sun
Roy
See also:
http://olosurfer-woodensurfboardsatpipeline.blogspot.com/2010/11/flex-frequency-and-harmonics-in.html
http://olosurfer-woodensurfboardsatpipeline.blogspot.com/2010/02/resonance-in-wooden-surfboards-balsa-vs.html
