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On the Physics of Balance in Rowing

To understand the remedy presented here for the noted deficiency in the current state of rowing exercise machines, it is helpful to understand the physics of balance in rowing. Boats float because the downward force of gravity exactly matches the upward force of buoyancy.

Gravity acts as if the total mass of the floating body and included rower(s) were concentrated at a single point, known as the center of gravity. Buoyancy forces also act as if applied at a single point, in an upward direction known as the center of buoyancy.

Additionally, the metacenter of a floating body is the intersection of buoyancy forces, represented by vertical lines, through the center of buoyancy at various roll positions. It represents the location of the longitudinal roll axis about which the floating body will rotate. If the shape of the floating body is semicircular in cross-section, the metacenter is simply at the center of curvature, roughly equivalent to the center point of the described circle. The hulls of rowing shells approach being semicircular in cross-section, therefore their metacenters lie approximately at the waterline, in the vicinity of the seat of the rower. Depending on the size and type of rowing shell, the metacenter of a given shell can be located inches below the seat (for narrow, small diameter single sculls) to inches above the seat (for shallower, large diameter recreational or training shells). Whether a body floats stably or unstably on the water depends on the relative positions of the metacenter of the boat, and the combined center of gravity of the boat and rowers. If the center of gravity is below the metacenter of a boat, as in the case of a hull with a wide shallow curvature, the boat will tend toward stability. If the center of gravity is above the metacenter of the boat, it will be unstable in direct proportion to that distance between the two points.

"Experience has shown us that, by first introducing young people to the land based rowing machine results in a faster adaptation to the water. However, rowers must still "learn the game" which means, amongst other things, mastering the skills required to row a boat. The skill needed to row a racing shell stems from the fact that the shell design has negative stability. All other boats or ships designed by a naval architect have positive stability, which means when the boat lists to one side, the forces that occur make the boat right itself. In a racing shell, once the boat lists then the forces occurring tend to make the boat capsize. A racing shell is most stable when it is upside down and the only reason it remains upright is due to the skill of the rower using the oars for stability."

"Improving Your Coaching Skills, Part 3"

“Boats float because the downward force due to gravity is exactly matched by the upward force due to buoyancy. Gravity acts as if the total mass were concentrated at single point, known as the center of mass, or center of gravity (CG). Buoyancy forces also act at as if applied at a single point, known as the center of buoyancy (CB). The CB coincides with the CG of the displaced fluid, which is not the same point as the CG of the floating body itself.”

“Basic Physics of Rowing” posted at

http://www.atm.ox.ac.uk/rowing/physics/basics.html
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