Thanks to the game's automatic sail management, we don't have to worry about changing sails by hand.
The criteria for change are multiple :
Boat options ( Foils / polish).
Wind speed ( TWS ) and its variations.
Wind angle ( TWA ) and its variations.
A coefficient called "overspeed" is applied to the speed of the sail to avoid untimely sail changes.
In fact, in "automatic sail" mode, in order for the game engine to change sails, the speed obtained with the new sail must be 1.4% higher than the speed of the current sail.
There are therefore areas of overlapping sails.
ITYC.fr offers you this spreadsheet to allow you to analyze more easily the sail changes