Lift, Drag, and Everything in Between
Each sail in the plan — main, jib, genoa, spinnaker, code zero — gets its own
force decomposition. Lift and drag coefficients are computed from the sail’s geometry
and the apparent wind angle. Those coefficients produce a drive force (forward) and a
side force (heeling) for every sail independently.
Sails don’t operate in isolation. When a headsail sits in the main’s wind shadow
at tight angles, the model accounts for blanketing — the reduction in effective
wind that the downstream sail actually sees. The shape of each foil matters too:
aspect ratio, overlap, roach. Different sail shapes produce different force profiles
at the same wind angle.
At the professional tier, loft-specific sail shapes feed directly into these
coefficients. The generic geometry is replaced with measured cut-sheet data.