GZ Curves
Sail Skills - Stability Free guide to ship and small vessel stability.  Aimed at small vessel users but suitable for professional mariners.  Diagrams, text and animations explaining stability: from righting lever to movement of liquid in tanks – the free surface effect.  Demonstrates adding weights to a vessel, heel and list.  Especially recommended for RYA examination candidates. Righting moment and lever A small sailing vessel heeled by the wind Diagram:  relating topweight in a sailing vessel to levers and moments Levers & moments Diagram:  a vessel heeled showing righting lever (GZ) A vessel recovering from inversion Inverted Stability Heel & angle of heel Diagram:  a vessel kept afloat by her buoyancy Buoyancy Diagram:  centre ofbuoyancy (CB) of a vessel heeling Centre of buoyancy (CB) Diagram:  a vessel at the angle of vanishing stability (AVS) Angle of vanishing stability (AVS) GZ Curve for a stiff and tender vessel - showing initial steepness of curves GZ Curves Centre of gravity (CG) Diagram: centre of gravity (CG) of a vessel heeling
Every penny helps … Stability Home>Stability Explained>GZ Curves GZ Curves  The sections on:  righting moment (RM) and lever (GZ) and angle of vanishing stability (AVS)  show that the GZ of a vessel varies with angle of heel.  The variation can be shown in a graph, simplified in this animation: back to top The variation of GZ with angle of heel can be shown in a graph GZ curve for a vessel shows very important information GZ Curve for a vessel that may swamp GZ curve has no significance beyond angle at which a vessel may swamp Few vessels have a positive GZ approaching 180° of heel.  It is achieved in RNLI lifeboats by fitting a large, water-tight superstructure: GZ curve for a RNLI lifeboat GZ curve for a RNLI lifeboat The ratio between the areas under the curve gives an important indication of stability:  Positive Area : Negative Area GZ Curve showing areas under the curve:  Positive Area:Negative Area GZ Curve showing areas under the curve:   Positive Area :  Negative Area GZ Curve for a stiff and tender vessel - showing initial steepness of curves
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GZ Curve for a stiff and tender vessel - showing initial steepness of curve