A mooring chain is guided for movement through the frame of a chain stopper along a pair of upright rails, with vertical links of the chain received between the rails and horizontal links of the chain riding on top of the rails. A pawl is swingably mounted on the frame above the rails with inner legs of the pawl engaging a horizontal link of the chain at opposite sides of an adjacent vertical link. The pawl has outer legs which extend downward to a release pin. The release pin has grooves positioned to receive the bottom ends of the outer legs and prevent the pawl from moving in a direction which will allow loosening of the chain, unless the release pin is freed for rotation through an angle of about 90.degree.. The release pin is connected to a trigger assembly including a spinner block which is normally held against rotation by a trigger finger. Movement of the trigger finger frees the spinner block and thereby allows the release pin to move from a pawl-engaging to a pawl-released position. The force of the chain on the inner legs of the pawl swings the pawl automatically as the chain loosens by sliding along the rails. The spinner block rotates freely, with no mechanism restraining it or the release pin.