Cuts & construction
Radial cut
Panels fanning out from the loaded corners, following the lines the load actually takes.
DutchRadiaalsnitour Dutch loft →
SpanishCorte radialour Spanish loft →
Load in a sail does not spread evenly. It runs in lines from the corners — look at the fans on any diagram on this site. A radial cut builds the sail from wedge-shaped panels that fan out of those corners, so the cloth's strong axis lies along the load rather than across it.
When all three corners get their own fan it is called tri-radial. It costs more: more panels, far more seams, more cloth wasted on the roll, more hours on the floor. What you buy is a sail that holds its designed shape under load and keeps holding it as it ages — the draft stays put.
It is the normal construction for spinnakers, where every panel is a gore fanning from the head, and it earns its keep on bigger or harder-driven upwind sails.