A control system (100, 200) for a marine vessel including a battery and an engine, the control system comprising: a portable device (1, 201) including a battery switch operator (14, 14a, 14b) and that is configured to transmit an authentication signal, which is a wireless signal for authentication; and a receiving device (2, 202) configured to be disposed on the marine vessel and that is configured to receive the authentication signal from the portable device (1, 201); and an engine controller that controls operation of the engine; wherein the battery switch operator (14, 14a, 14b) is configured to receive an input operation of opening or closing a current path (3, 115, 115a, 115b, 203) between the engine controller and the battery; the portable device (1, 201) is configured to transmit a switch control signal, which is a wireless signal to open or close the current path (3, 115, 115a, 115b, 203), to the receiving device (2, 202) based on the input operation on the battery switch operator (14, 14a, 14b); and the control system (100, 200) is configured to perform authentication control processing related to control of the marine vessel based on the authentication signal from the portable device (1, 201), and control opening or closing of the current path (3, 115, 115a, 115b, 203) based on the switch control signal from the portable device (1, 201), characterized in that the battery switch operator (14, 14a, 14b) is configured to transmit the switch control signal to the receiving device (2, 202) when receiving one of a long press operation in which a period during which the input operation is performed on the battery switch operator (14, 14a, 14b) is a first period and a short press operation in which a period during which the input operation is performed on the battery switch operator (14, 14a, 14b) is a second period shorter than the first period, and transmit the authentication signal to the receiving device (2, 202) when receiving the other of the long press operation and the short press operation. a portable device (1, 201) including a battery switch operator (14, 14a, 14b) and that is configured to transmit an authentication signal, which is a wireless signal for authentication; and a receiving device (2, 202) configured to be disposed on the marine vessel and that is configured to receive the authentication signal from the portable device (1, 201); and an engine controller that controls operation of the engine; wherein the battery switch operator (14, 14a, 14b) is configured to receive an input operation of opening or closing a current path (3, 115, 115a, 115b, 203) between the engine controller and the battery; the portable device (1, 201) is configured to transmit a switch control signal, which is a wireless signal to open or close the current path (3, 115, 115a, 115b, 203), to the receiving device (2, 202) based on the input operation on the battery switch operator (14, 14a, 14b); and the control system (100, 200) is configured to perform authentication control processing related to control of the marine vessel based on the authentication signal from the portable device (1, 201), and control opening or closing of the current path (3, 115, 115a, 115b, 203) based on the switch control signal from the portable device (1, 201), characterized in that the battery switch operator (14, 14a, 14b) is configured to transmit the switch control signal to the receiving device (2, 202) when receiving one of a long press operation in which a period during which the input operation is performed on the battery switch operator (14, 14a, 14b) is a first period and a short press operation in which a period during which the input operation is performed on the battery switch operator (14, 14a, 14b) is a second period shorter than the first period, and transmit the authentication signal to the receiving device (2, 202) when receiving the other of the long press operation and the short press operation.