Surf science

[stoo_pid]

What's the science behind surfing (in the sea, not online)?  Obviously if you're surfing along a wave you keep going, but when the wave stops, you sink.  Scientifically speaking why does a moving body of water keep things afloat that would otherwise sink?

 

[apricot2]

Surfing, the greatest spectator sport ever.  It's the momentum that SOMETIMES carries you forward.  It's the difficulty that makes it such fun.  There is an excellent explanation in the Stormrider book

[Ralph]

Very simply, the board is moving "downhill" on the face of the wave, so the rider is using gravity on a sloping surface to get some forward momentum together, much as a car will roll down a hill. When the rider has the momentum, the board starts acting very like a powerboat, where there is hydrodynamic lift on the underside of the board which supports both it and the rider. When the board looses forward speed and so looses the hydrodynamic lift, it is reliant on hydrostatic displacement (Archimedes in the overflowing bath?). Since a surfboard only has a displacement of say 60 litres (wild guess) and you need 1 litre of displacement for every kilo of payload, more or less, the weight of the rider is going to sink the board.