Abstract: A stern tube sealing assembly and a seal ring thereof has a key part having an inverted V-shape, a front step part on the front side, and a back step part on the back side thereof. The seal ring width in a propulsion-shaft axis direction becomes thinner in the transition area from the key part toward a heel part. The inner diameter of the key part at the back step part is greater than that of the key part at the front step part. The ring has a lip part having a V-shaped lip tip protruding inwardly in the radial direction and a spring groove having a semicircular cross-section. The center of the spring groove is nearer to the inboard side than the lip tip, by an offset in the axis direction, the offset being within approximately 10% of the orthogonal projection length of the width of the lip back.

Abstract: (Means) A seal ring in which an apex part of the key part is formed so that the cross-section profile regarding the apex part forms a reversed V-shape toward the outside in the radial direction; the summit T of the reversed V-shape is formed as the middle center T of the apex part; a step part on the front surface side of the key part and a step part on the back surface side of the key part are formed so that the width of the seal ring in the axis direction of the ship propulsion shaft becomes thinner in the transition area from the key part toward the heel part; the inner diameter of the key part at the step part on the back surface side of the key part is greater than the inner diameter of the key part at the step part on the front surface side of the key part; a lip tip of the lip part forms a V-shape protruding inward in the radial direction and a spring groove having a semicircular cross-section in which a ringed spring is formed in the lip part; the center regarding the spring groove is arranged so as t