Abstract: A system to control a watercraft including an engine includes a first temperature sensor and a controller. The first temperature sensor is operable to detect a temperature of the engine. The controller is configured or programmed to obtain the temperature of the engine either upon an activation of the controller or a start of the engine. The controller is configured or programmed to estimate an environmental temperature of the watercraft based on the temperature of the engine obtained either upon the activation of the controller or the start of the engine.

Abstract: A marine cooling system performs a temperature adjustment of an object to be cooled such as an internal combustion engine of a marine vessel. The marine cooling system includes a water supply flow passage to supply cooling water to the object, a water drain flow passage to drain the cooling water from the object to reduce an amount of the cooling water that contacts the object, and a flow passage controller to shut off the water to the drain flow passage.

Abstract: A marine cooling system performs a temperature adjustment of an object to be cooled such as an internal combustion engine of a marine vessel. The marine cooling system includes a water supply flow passage to supply cooling water to the object, a water drain flow passage to drain the cooling water from the object to reduce an amount of the cooling water that contacts the object, and a flow passage controller to shut off the water to the drain flow passage.