Comment by pmontra

The blue cones are probably the wind coming to the boat but there is a wall of cones a little further away, visible by zooming out. Those cones don't have the same directions of the ones close to the boat. It's probably apparent wind (close to the boat) and real wind (further away.) It would help to start with a zoom level with both winds visible.

The biggest problem that is puzzling everybody is that speed never changes. I eventually decided that this is because the app calculates the setup of the mainsail to get the desired boat heading and speed given the wind. If you keep the heading constant and change the boat speed you see that the sail rotates around the mast.

It's the opposite of what we do when sailing: we set the sail to a shape and direction (let me use these terms) to go somewhere. In this simulator we do it backwards and adjust the wind to get the sail into a shape and direction.