Stern tube sealing device

A stern tube sealing device which seals an outer periphery of a propeller shaft in a marine vessel, said stern tube sealing device comprising:

• a seal housing through which said propeller shaft is inserted;
• a first seal ring that is arranged in a first seal ring chamber formed in said seal housing, and has a sealing surface which slides with respect to a wall surface of said first seal ring chamber, or an outer peripheral surface of said propeller shaft;
• and
• a second seal ring that is arranged in a second seal ring chamber formed in said seal housing at an inboard side of said first seal ring chamber, and has a sealing surface which slides with respect to a wall surface of said second seal ring chamber, or the outer peripheral surface of said propeller shaft;
• wherein said first seal ring chamber is in communication with an outside of the marine vessel, and
• said first seal ring chamber and said second seal ring chamber are in communication with each other through sliding portions between the wall surface of said first seal ring chamber or the outer peripheral surface of said propeller shaft and the sealing surface of said first seal ring;
• wherein outboard water is filled into said first seal ring chamber;
• clear water from an on-board water tank is filled into said second seal ring chamber so that clear water being received in the second sealing chamber is sealed by the first seal ring and the second seal ring, wherein the pressure of the clear water in said second seal ring chamber is lower than the pressure of the outboard water in said first seal ring chamber;
• and
• a drain pipe connected directly to an inside of the second seal ring chamber that receives clear water and including a drain valve in the drain pipe
• wherein each sealing ring has a lip portion, the lip portion of one of the sealing rings directly contacts an inboard side wall surface of one of the respective first and second seal ring chambers and slides with respect to the inboard wall surface.