The bulb is an appendix to improve wave resistance. It works well in a certain range of V / √ L v – boat speed and L is the length. Works very well on ships that has constant velocity.
The bulb is to improve the formation of waves produced by the boat so that the energy lost in this formation is reduced and energy saved is used to increase speed. As the speed of sailboats is a function of wind speed, the introduction of a bulb should be studied very well to not increase the wave resistance outside the speed range in which it is really effective.
But it is an open field in search of solutions for a good performance. The introduction of this boat with bulb shows that australians are audacious, technicians, and competent, they were not the first to take the America’s Cup in the USA, exactly with the introduction of several new technologies.
Photo copied from website forum italia: