THIS CURVE OF STATICAL STABILITY FOR A SHIP IN PARTICULAR CONDITION OF LOADING IS OBTAINED BY PLOTTING THE RIGHTING LEVERS AGAINST ANGLE OF HEEL.
THE ABOVE CURVE IS FOR POSITIVE INITIAL METACENTRIC HEIGHT
THE ABOVE CURVE IS FOR NEGATIVE METACENTRIC HEIGHT
FOLLOWING INFORMATION IS PROVIDED BY THE CURVE:-
- RANGE OF STABILITY :- THE RANGE OVER WHICH THE SHIP HAS POSITIVE RIGHTING LEVER I.E 0-86 IN FIRST PIC AND 18-90 IN SECOND PIC.
- ANGLE OF VANISHING STABILITY :- IS THE ANGLE OF HEEL AT WHICH THE RIGHTING LEVER RETURNS TO ZERO, OR THE ANGLE AT WHICH THE SIGN OF THE RIGHTING LEVERS CHANGES FROM POSITIVE TO NEGATIVE I.E 86 DEGREE IN FIRST PIC.
- MAXIMUM GZ:- IS OBTAINED BY PLOTTING A TANGENT TO THE HIGHEST POINT OF THE CURVE I.E 0.63 MTRS WHICH OCCURS AT ABOUT 42 DEGREE.
- INITIAL GM:- CAN BE FOUND BY DRAWING A TANGENT TO THE CURVE THROUGH THE ORIGIN AND THEN ERECTING A PERPENDICULAR THROUGH THE ANGLE OF HEEL OF 57.3 DEGREE. THE 2 LINES ARE ALLOWED TO INTERSECT AND THE VALUE OF GZ IS NOTED WHICH IS THE INITIAL GM.
- POINT OF INFLECTION/CONTRAFLEXURE:- IT IS THE ANGLE AT WHICH THE CURVE GOES FROM CONCAVE TO CONVEX. PHYSICAL SIGNIFICANCE OF THIS POINT IS THAT IT IS THE ANGLE AT WHICH THE DECK JUST TOUCHES THE SEA.
IN THE SECOND FIGURE OF NEGATIVE METACENTRIC HEIGHT, AT AN ANGLE LESS THAN 18 DEGREE THE RIGHTING LEVERS ARE NEGETIVE AND BEYOND 18 DEGREE TO 90 DEGREE ITS POSITIVE. HENCE 18 DEGREE IS THE ANGLE OF LOLL. INITIAL GM CAN BE PLOTTED AGAINST 57.3 DEGREE.
NOW THE QUESTION ARISES IS THAT WHY WE TAKE INITAL GM AT 57.3 DEGREE. WELL THE ANSWER IS THAT 57.3 DEGREE = 180/PIE=180/3.14=57.3 DEGREE
One response to “STATICAL STABILITY CURVE”
Hey, great explaination about the importance of those graphs! Question is: is it always 57.3° the angle at which we measure the value of metacentric height at different angles? (And thus maybe prometacentric heights)