holden wrote:@davesails7: i disagree with your conclusions. with kitesurfing it is almost allways about dynamic lift. volume only creates static buoyancy. you only need static buoyancy when standing on board with virtually no speed at all. for example when you do a tack and fail to loop the kite on time volume prevents you from sinking.
True, dynamic lift starts to support you as soon as you start moving, but it doesn't become all dynamic lift right away. At slow speeds your weight is supported by a combination of both. As you speed up a larger portion of your weight is supported by dynamic lift (proportional to area as you said) and less by the buoyant force of the submerged volume.
I haven't ridden a foil board yet (so this might all be total BS ), but on my raceboard the volume really helps to get going in the ultra light wind. When it is really light I can only get going if I start with the back foot in the center of the board and use the buoyancy of the board while I sine the kite up and down. Between dives of the kite the board can come to almost a complete stop, but the buoyancy from the volume keeps me afloat and in the correct position until I can get up enough speed (or get a gust) to start planing, put my back foot in the strap, and load up the fins.
I'm guessing you could do the same on a foilboard with extra volume in very light winds. It seems like by the time you have enough speed/power to get the board to plane and provide enough dynamic lift, you would have had enough speed/power to get lift from the foil. The foil provides dynamic lift, but is more efficient than your board is. A little more than 1 square foot of foil can support you in <10 knots where if you assume half of a light-wind twin tip is planing surface you're at over 3 square feet of planing area.
Also when racing you need the volume in your foilboard to slow yourself down at the start line, but still be ready to take off at the gun. Another thread had a discussion about a race that included raceboards and foil boards on the same course. The raceboards were able to slow to an almost stop on the line waiting for the gun, but the foilboards had to come in with speed, so the foilboards couldn't get as good of a start. They were always starting behind the raceboards.
Again, I've never even ridden a foil yet, so I could be totally wrong. From my raceboard experience though the extra volume to get up to speed in underpowered conditions and maneuver before a race makes a lot of sense to me. I've very interested to see how this all works out once the Foil races start in a few months