optimal rowing shell

[bugonwheels1]

Okay, so my question is, for a rowing shell (very large length/beam ratio) that will travel at speeds about 4-4.5 m/s (for racing), is it better to have a longer hull or a short hull, taking into account frictional and wave drag?

[frosh]

There is an optimum length to beam ratio which will depend on many factors. Simple calculation of the hull cross sectional area immersed when in use will indicate a measure of the wave making resistance. Surface area of the hull skin that is immersed will indicate a measure of skin friction which is also a drag force. The greater the total displacement the greater will be both drag forces. A hull designed too short will have a large wave making drag compenent, while a hull too long will have excess skin friction, even though it has a theoretical higher speed potential. It is often impossible to drive the hull up to this theoretical speed due to insufficient manpower. Best policy is to study some proven designs and use a design that fulfills a similar purpose to what you intend as a starting point for your own design. Some very general rules would be as follows: Lighter displacement is faster. Narrow beam is faster. The least immersed cross sectional surface is faster. This means semicircular underwater sections are quicker than hard chine. Use actual length of existing designs as a guide. The very quickest hull shapes are also inherently less stable. As you can see there is no simple formula.

[CDBarry]

Look first at Saunders "Hydrodynamics of Ship Design". There are a number of subsequent papers in many areas. Note that Carl Scraggs and Bruce Nelson did some interesting work that considers the effect of the accelleration and deceleration produced by rowing, which actually has a significant efect on shell desigen.