In a graph of acceleration versus net force, the slope of the graph represents the inverse of the mass of the boat. This is derived from Newton's second law of motion, \( F = ma \), which can be rearranged to \( a = \frac{F}{m} \). The slope (which is the change in acceleration divided by the change in force) indicates that for a given force, acceleration increases inversely with mass. Therefore, the correct response is:
the inverse of the mass of the boat.