WE KNOW THAT:-
MOMENT OF STATICAL STABILITY= W*GZ TONNES METRES
WHERE W = DISPLACEMENT OF SHIP IN TONNES
GZ= RIGHTING LEVER
AND GZ = GM*SIN(ANGLE OF HEEL)
HENCE MOMENT OF STATICAL STABILITY DEPENDS ON GM
NOW IF THE SHIP IS HAVING HIGHER GM THEN MOMENT OF STATICAL STABILITY IS ALSO GREATER AND HENCE IT TAKES LARGER MOMENT TO INCLINE THE SHIP AND WHEN INCLINED IT WILL COME BACK TO INITIAL POSITION QUICKLY AS MOMENT OF STABILITY STABILITY TENDS TO STABILIZE THE SHIP. HENCE THE TIME PERIOD OF SHIP WILL BE LESS. HENCE SHIP TRY TO ROLL MORE QUICKLY AND VIOLENTLY. THIS CONDITION IS KNOWN AS STIFF SHIP.
TIME PERIOD OF A SHIP IS THE TIME TAKEN BY THE SHIP TO ROLL FROM ONE SIDE TO THE OTHER AND BACK AGAIN TO THE INITIAL POSITION.
NOW IF GM IS COMPARATIVELY SMALL THEN MOMENT OF STATICAL STABILITY IS LESS AND HENCE SHIP WHEN INCLINED WILL BE INCLINED MORE EASILY AND WILL NOT TEND TO RETURN QUICKLY TO ITS INITIAL POSITION. HENCE TIME PERIOD IS MORE. THIS CONDITION IS CALLED TENDER SHIP.