What is a GZ curve?
The curve of statical stability, or GZ curve as it is most commonly referred to, is a graphical representation of the ship’s transverse statical stability.
How is GZ calculated?
GZ=GM sin φ and is called the righting lever. GM is known as the metacentric height. For a given position of G, as M can be taken as fixed for small inclinations, GM will be constant for any particular waterline.
What is GZ righting lever?
Righting lever (GZ) is defined as the horizontal distance, measured in metres, between the centre of gravity (G) and the vertical line of action of the buoyancy force (Bf) acting through the centre of buoyancy (B1) when the ship is heeled.
What is KN curve?
Cross Curves of Stability / KN Curves: The vertical position of centre of gravity (G) of the ship is not always fixed. It changes with every voyage, depending on the loading conditions and the amount of ballast. The CG of the ship also changes when the ship is in transit.
How do you get gm from GZ curve?
The following data can be extracted from a GZ curve; The metacentric height (GM) is found by drawing a perpendicular line at 57.2° (1 radian) where this line intersects the GZ Curve a right angle is drawn and where this intersects the GZ axis of the graph the GM can be found in this case it is 1.0 metres.
What are GZ and KN curves?
THESE CURVE ARE SAME AS GZ CURVE WITH ONLY A DIFFERENCE THAT IT IS PLOTTED FOR AN ASSUMED KG= 0 MTRS. KN BEING THE RIGHTING LEVER MEASURED FROM THE KEEL. TO OBTAIN RIGHTING LEVER FOR A PARTICULAR DISPLACEMENT AND KG THE VALUE OF KN ARE FIRST OBTAINED FROM THE CURVE AT THE DISPLACEMENT CONCERNED.
What is the minimum allowable value for GM?
For a typical ship of those which were reported to experience loss of deck loads in heavy weather, the minimum GM according to the Timber Code could be as low as 0.1 m, but in order to comply with all the requirements of the ordinary intact stability criteria according to the IMO Intact Code a minimum GM of about 0.8 m …
How do you find the initial GM of a GZ curve?
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.
What is the GZ curve on a 35 foot boat?
Righting arm (GZ) stability curve for a typical 35-foot cruising boat. The angle of maximum stability (AMS) in this case is 55 degrees with a maximum GZ of 2.6 feet; the angle of vanishing stability (AVS) is 120 degrees; the minimum GZ is -0.8 feet.
Calculating the value of GZ, at specified angles of heel for a ship’s particular condition of loading, will allow a curve of statical stability, or GZ curve, to be produced. The greater the values of GZ, the greater will be the area under the curve.
How to draw the curve of statical stability using GZ?
> To draw the curve of statical stability (discussed above), we need GZ values for various angles of heel. For this we use the GZ cross curves of stability. > The graph where the righting lever (GZ) is plotted against the displacement. > These curves are plotted for an assumed KG, tabulating GZ values for various displacements and angles of list.
What is the GZ correction for kg?
> This correction is positive if the actual KG is less than the assumed KG and vice-versa. > After obtaining the GZ values at various angles, the curve of statical stability is prepared. Same as the GZ cross curves and also used to get the GZ values for making the curve of statical stability.