I just posted another custom where the customer notices the lift , instant speed = 0 drag
No concaves and at very low end - Florida mush
Contradicts all he has read
Yes of course Greg, all surfboards generate lift whether they be flat, V bottom, concave, inverted V whatever. If they didn't generate lift then our surfboards would become submarines.
So no doesn't contradict all what I read and more importantly experienced. I will have another go at trying to get across how I think things work and I will try and do it without referring to any "high school physics".
Planing hulls have been shown to have different lift distributions using empirical measurement - not science prediction. The underneath of boats whether they be dead flat, shallow V, deep V, concaved V have a mixture of high pressure, low pressure and even suction, however overall balancing out the pressure and suction the lift is winning because the boats when going fast enough rise to the plane instead of head towards the bottom.
What the different bottom shapes do is influence where the low pressure and high pressure areas are. Naval architect Lindsay Lord towed model hulls of varying sizes, some of them loaded with instrumentation. The excerpt of the book I have read didn't say what the pressure instruments were although a look around on a boat forum thought they were diaphragm sensors. He determined that there were different distributions for different hull shapes. This was quite a long time ago, but his work was largely validated at a later date by another naval architect called Daniel Savitzky. For boats of simple shapes - panel V with chines Savitzky's work is still used today when designing them.
So what I am saying is that concave surfboard will have a different pressure (lift) distribution to a flat bottom or a V bottom and experience from riding all three has told me something. During that transition period when concaves were starting to be put into thrusters I used to get confused when riding them and trying to determine what the concave was doing, partly because different surfboards are never that all other things equal perfect comparison.
However things became clear after riding a concave when I borrowed a McCoy nugget deep rolled V to deep panel V. The roll is something like 1cm. Despite its super wide tail the nugget would tip from side to side with ease with heel toe pressure this can only mean that there was less water pressure (lift) at the rails than a concave. As to whether it had more overall lift or less overall lift than a concave I get confused thinking about that because if two board are both supporting the same weight rider then they must be generating the same lift!
Anyway after the Nugget experience I knew what to look for when comparing a flat bottom thruster with a light concave - the rail of the light concave wants to pop to the surface a bit more quickly - we could say that the there is more lift at the inside rail of a light concave or more pressure if you like or if you want to call it something else altogether - you have used the "clawing" effect - I have always said I am happy with that as long as there is some common understanding. I call it lift you call it the clawing effect. I have since come up with explanations as to why boards behave like that, but I won't go into that