What is Newtons 2nd Law?
Force is equal to mass times acceleration. As force on an object increases, acceleration will increase. As mass increases without a change in force, acceleration will decrease. As you are windsurfing, the wind is the force acting on the sail. Assuming your mass is constant an increase in wind will increase the acceleration of the board and impress the onlookers on the beach. If your mass increases, like a shark attaching itself to your leading edge, and the wind doesn’t increase, your acceleration will decrease (slow down) allowing you to desperately dive and try to swim for shore. If the shark adds five times to your mass, then the force will be one fifth of what it was. So, swim like crazy and hope the shark goes for a ride.