Physics of Sailing :: physics sail boat sailing boating

A boat floating can be greatly appreciated, especially if you are in the boat at the time. But what keeps a boat from sinking? Physics can explain these concepts. There are many forces that act on a sailing ship to put it in motion, but the buoyant force is what is required to keep the boat from sinking. A buoyant force is the normal force that pushes up on the boat supporting its weight in a fluid. The buoyant force "equals the weight of the fluid displaced by the object."(pg.427, Serway and Jewett) This concept is Archimede's Principle. The pressure on an object in a fluid varies with the depth of that part of the object in the fluid. B=(P b – P t)A = (Ï  fluidgh)A = Ï  fluidgV B=Buoyant force P b=pressure at bottom P t=pressure at top A=area of bottom face Ï  fluid=fluid density g=gravity h= height V=volume of fluid displaced by object (formula from pg. 428, Serway and Jewett) "The fraction of the volume of a floating object that is below the fluid surface is equal to the ratio of the density of the object to that of the fluid."(p.429, Serway and Jewett) V fluid/Vobj = Ï  obj/Ï  fluid Vobj=volume of the object Ï  obj=density of the object Buoyancy of the craft is created by the shape of the hull, but also with buoyant materials in specific places. Air tanks, buoyancy bags, and polystyrene blocks are all used to add buoyancy to a boat. The figure below shows how the buoyant material should be distributed and the effects if it is not. figure from The Handbook of Sailing The distrubution of buoyancy is key to having the boat float properly. Bernoulli's principle is that the air moving past a foil, an object that has one curved side and one flat side, will take longer to move past the curved side than the flat side of the foil. This will cause the flat side to have higher air pressure and to exert a force on the object. The force cause a planes wing to lift and a sail to push a boat. "With the wind pushing on one side of the sails and the water pushing on the other side of the centerboard, the boat moves forward." (p. 35, Dellenbaugh) The angle at which sailing is important. A 45 degree angle to the wind is the most effective angle. Wind is what propels a sailing ship so weather has a large impact on the craft. Certain weather conditions are not suitable for sailing or specific crafts.