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>Righting Moment & Lever The relative movement of centre of buoyancy (CB) and centre of gravity (CG) results in buoyancy and weight acting to restore vessel to upright (at smaller angles of heel) The vertical separation between the lines of force of: buoyancy and weight is known as the righting lever - the GZ. It is shown as such on diagrams. It varies with angle of heel: Righting lever (GZ) Effect of adding weight on righting lever (GZ) Adding weight to a vessel: high up reduces the GZ and hence stability low down increases the GZ and stability The effect on GZ is increased by adding larger weights: higher - such as gear at the top of a mast or lower - such as keels and engines back to top
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