A control apparatus for a hull with a four-cycle engine installed thereon can perform engine stop processing by quickly detecting a turnover state of the hull while suppressing a turnover determination delay due to noise superposition. The apparatus includes a turnover determination part that determines, based on a detection signal from a turnover detection switch, whether the hull is in a turnover state, and an engine stop part that stops the engine upon determination of a final hull turnover state. The turnover determination part increments a detection ratio counter each time a detection signal indicative of a hull turnover state is input thereto, counts up a continuous turnover counter each time the detection ratio counter value indicates a predetermined determination ratio value or above. When the continuous turnover counter value reaches the predetermined determination value or above, the turnover determination part determines that the hull is in the final turnover state.