A ship propulsion apparatus comprising: a power device ; a gear pump , wherein the gear pump comprises a drive gear , a driven gear engaged with the drive gear , a first end cover , and a second end cover defining a receiving groove , wherein the drive gear and the driven gear are received in the receiving groove between the first end cover and the second end cover , the first end cover being stacked on the second end cover ; a coolant supply providing a fluid as a coolant; a supporting rod defining a coolant passage that communicates with the gear pump in series, wherein the supporting rod and its coolant passage are to be partly immersed in water when the ship propulsion apparatus is working; wherein the ship propulsion apparatus defines a closed fluid circuit, the closed fluid circuit circulating the fluid provided by the coolant supply through rotation of the drive gear and the driven gear of the gear pump , so that the fluid flows through the gear pump , the coolant supply and the coolant passage of the supporting rod ; and wherein the gear pump forms two independent passageways, both independent passageways entirely contained in the gear pump , the two independent passageways each communicate with the coolant passage in the supporting rod , one of the two independent passageways to pass the fluid into the supporting rod and the other one of the two independent passageways to receive the fluid from the supporting rod , and one of the two independent passageways is formed through the drive gear and the driven gear and is at least in part formed by the receiving groove of the second end cover . a power device ; a gear pump , wherein the gear pump comprises a drive gear , a driven gear engaged with the drive gear , a first end cover , and a second end cover defining a receiving groove , wherein the drive gear and the driven gear are received in the receiving groove between the first end cover and the second end cover , the first end cover being stacked on the second end cover ; a coolant supply providing a fluid as a coolant; a supporting rod defining a coolant passage that communicates with the gear pump in series, wherein the supporting rod and its coolant passage are to be partly immersed in water when the ship propulsion apparatus is working; wherein the ship propulsion apparatus defines a closed fluid circuit, the closed fluid circuit circulating the fluid provided by the coolant supply through rotation of the drive gear and the driven gear of the gear pump , so that the fluid flows through the gear pump , the coolant supply and the coolant passage of the supporting rod ; and wherein the gear pump forms two independent passageways, both independent passageways entirely contained in the gear pump , the two independent passageways each communicate with the coolant passage in the supporting rod , one of the two independent passageways to pass the fluid into the supporting rod and the other one of the two independent passageways to receive the fluid from the supporting rod , and one of the two independent passageways is formed through the drive gear and the driven gear and is at least in part formed by the receiving groove of the second end cover . <EOS>