In a graph of acceleration versus net force, the slope represents the mass of the boat. This relationship is described by Newton's second law of motion, \( F = ma \), where \( F \) is the net force, \( m \) is the mass, and \( a \) is the acceleration. Rearranging this equation gives \( a = \frac{F}{m} \), indicating that acceleration (a) is directly proportional to net force (F) and inversely proportional to mass (m). Therefore, the slope of the graph (which is \( \frac{a}{F} \)) would be \( \frac{1}{m} \), so if we are looking at the slope in terms of acceleration versus force, it directly indicates the mass of the boat.
Hence, the correct response is: the mass of the boat