The selection of a propeller for a particular boat is typically a multistep process involving numerous trade-offs. A simple specification of prop diameter and pitch, for example, 18 by 16 inches, three blade (the first number is prop diameter, the second designates pitch) is only a starting point. A prop specification will include "hand (left or right, the rotation direction), diameter, pitch, number of blades, blade area, blade section (ogival or airfoil), blade skew and rake, "cup and the dimensions of the prop shaft on which it will be installed. Props for sailboats may allow manual adjustment of blade pitch or provide automatic pitch adjustment. Feathering props are popular, especially among sailors who race their boats. Controllable-pitch feathering props are increasingly common on large sailboats, along with non-feathering controllable pitch props installed on many motoryachts.