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>Centre of Gravity Diagram: centre of gravity (CG) of a disc and a sheet of metal Diagram: centre of gravity (CG) of simple solid objects Diagram: centre of gravity (CG) of simple tube and a shape made of wire Centre of gravity (CG) of a disc and a sheet of metal or simple solid objects: Even an hollow shape has a CG. For example: a simple tube’s CG is on its centre-line, while even a completely open shape made of wire has a CG: Centre of gravity (CG) of simple solid objects Centre of gravity (CG) of simple tube and a shape made of wire Remember, the CG is an imaginary point, through which the weight of an object is considered to act: CG is an imaginary point through which an object's - here a vessel’s - weight is considered to act Adding weight to a vessel effects the position of her CG. Note that as weight is added to this vessel, her CG moves towards the CG of the added weight: Diagram: point of action of a suspended object Point of action of a suspended object Effect on a vessel’s CG of lifting and moving an heavy object Some fishing vessels trawl with their nets suspended from booms. This can make them very vulnerable should their nets get caught on an obstruction on one side. This vessel would lower her booms to fish: A fishing vessel with booms A fishing vessel with booms The animation of the merchant vessel reminds that adding weight to one side of a vessel's centre-line also has an effect on the position of her CG As the imaginary CG of an object results from its components, it could even be completely outside a body: Diagram: CG of complex shapes can be outside the object CG of complex shapes can be outside the object back to top Effect on vessel’s CG of adding weights Effect on CG (and trim) of adding weight towards the end of a vessel
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