Hi pilgrim,

Ok, if you cant get lighter than 200g/sqm your original layout might be a good solution in fact. Didn't know you are limited by availability...

Cavitation depends on speed and load... most people think, that the rudders stall while sailing fast downwind, but actually going 17kts and keeping the boat on course let the boards cavitate (sometimes). If you see bubbles in the water it is cavitation. Some are from the tip vortex, you can´t avoid that, but if you see bubbles at the leading edge, than is cavitation. The cavitation triggers than the stall. A good foil will not cavitate, some designers reduce thickness to achieve that, but your rudder will be less strong or must be build heavier and it will have a lower maximum lift coefficient, hence needs to be larger.


Water has a higher viscosity than air, hence the Reynoldsnumbers are higher. That's why dedicated RC plane foils are not suited for boards and rudders. Classic airplane foils as the NACA 00xx works once you are fast enough without turbulator.

IMO boards and rudders will never have a laminar boundary layer, sinvce the surface water itself is already turbulent. Hence the foils which I designed are all turbulent foils.

Hope my answer wasn"t too nerdy...

Cheers,

Klaus