RE: Cutouts - fact or fashion
Hi Steve C,
I guess it's more experimental than scientific; otherwise, probably there would be some scientific explanations readily available. Nevertheless, I think there are no big mysteries in board designs and shapes usually speak for themselves.
As for the cutout configuration issue, I think that probably "thin" cutouts provide for a more gradual transition from "subplaning" to "full planing"; while deeper ones should generate a sharper acceleration when the central part of the hull gets free form the water flow, enabling for a quicker adaptation of wetted surface to the higher speeds. Probably, thin cutouts provide for more even performance spectrum while deeper ones provide for more "powerful/extreme" performances in a narrower speed range.
Last Spring tests from PlancheMag seem to confirm this idea, with regard to the F2 SX S (strong acceleration and good control in high winds, but less low end) and the JP Slalom 94 II (strong acceleration and high low end performances, less control at high end); both with deep cutouts. Other boards with no cutouts, such as the Sonic 85/95, were praised for their wide performance spectrum.
Of course, this can not be 100% valid as many other elements contribute to the performance spectrum, rocker line in first.
As for turning, any vertical surface in the water flow would tend to impair it, but cutouts surfaces are comparatively small with regards to fin and rails surfaces; so their influence should not be that much.
As for high wind / bump and jump boards, I guess that the drawn out outer outline provides good tracking for high speed jibes and the stepped bottom provides a short, wide planing surface with a sharp release for acceleration and speed. The step/cutout shape with small longitudinal vertical surface should not impair turning abilities.
I really like this discussion and I would really love to see some contributions from board designers.