In a graph of acceleration versus net force, the slope of the graph represents the inverse of the mass of the boat. This is based on Newton's second law of motion, which states that \( F = ma \) (force equals mass times acceleration). Rearranging this equation gives \( a = \frac{F}{m} \), indicating that acceleration is directly proportional to net force and inversely proportional to mass. Therefore, the correct response is:
the inverse of the mass of the boat.