An aerodynamic trim modeling tool designed to maximize yacht velocity made good (VMG) across varying apparent wind angles and wind speeds.
Sail trim is not merely about pulling ropes until wrinkles disappear; it is a fluid dynamics challenge involving boundary layer airflow, lift-to-drag ratios, and foil depth placement. When a yacht sails upwind, the mainsail and headsail act as a dual-element asymmetric hydrofoil system.
The interaction between the leech of the jib and the entry of the mainsail creates the "slot effect." An improperly tensioned backstay causes fore-stay sag, which dramatically increases headsail entry draft, generating excess drag, rounded steering feel, and excessive heel without proportional forward vector thrust.
Draft Location Index (DLI) = (Distance to Max Draft Depth / Total Chord Length) × 100.
Optimal upwind performance requires DLI maintained between 42% and 48% back from the luff.
As wind velocity increases, aerodynamic drag increases with the square of wind velocity ($v^2$). To prevent rounding up and maximize Velocity Made Good (VMG), the rig must be flattened through four primary control controls:
For further empirical modeling data on hydrodynamic rigging loads and sail canvas structural dynamics, consult official offshore rating and technical authorities: