in the direction of extension when sailing the propelling force from the external propelling device 1 and the compressive force generated by the weight of the tilt damper are both applied to the tilt damper 10 as a result if the movement of piston 12 in the direction of the retraction of piston rod 15 could securely be restrained substantially the position of the external propelling device 1 can be held stable at the predetermined ideal angle if unwanted impact overload were applied to the tilt damper 10 in the direction of extension as a result of a collision with a boat or obstacle like lumber floating in water for example then the tilt damper 10 allows oil to flow out of extension side oil chamber 14 through check valve 21 this causes the piston 12 to move thus allowing piston rod 15 to provisionally extend before eventually absorbing the shock simultaneously as a result of the movement of piston 12 the retraction side oil chamber 13 expands and generates a negative pressure however if the differential pressure against the inner pressure of the gas chamber 17 does not exceed the predetermined operating pressure of the relief valve 20 the relief valve 20 remains closed as a result the tilt damper 10 extended by the impact is relieved of the load before eventually returning to its original position by virtue of stability which is generated by the negative pressure of the retraction side oil chamber 13 and applied to piston 12 in the direction of retraction when the relief valve 20 is opened due to an impact incurred by.