The wind you feel on the sails is the wind relative to the moving boat. Changing a sail’s angle changes its lift, drag and turning effect. The keel resists sideways motion, while the rudder turns the boat as water flows past it. Different trim on the main and jib can change the boat’s balance. A boat cannot simply point straight into the wind and accelerate forward; change course and tack across it.

This is a lightweight teaching model: a smooth evolving wind field, approximate lift/stall/drag curves, lumped hull and keel resistance, rudder forces and planar rigid-body motion. It does not predict real boat performance, waves, heeling, currents or detailed fluid flow. The buoys are visual references rather than obstacles. Sail angles are measured from the boat’s aft centerline, toward port or starboard. Reset restores the original wind and boat state. Nothing is saved or sent to a server.

Reference basis: NASA lift equation · Cal Sailing Club sailing handbook.