A sailboat harnesses the energy of wind to propel it through water. The sailboat’s keel prevents it from slipping sideways in the water and changing course. Sailboats today are much more refined than those of the Arabs thousands of years ago. The improvement has less to do with the sail than with the hull design.
When a sailboat moves slowly through the water, it generates bow waves with wavelengths that extend out from its length. As the boat speeds up, its bow waves get shorter in wavelength and it generates fewer wave crests and troughs. At a speed called hull speed, its bow waves have a length equal to its water line, and it has just one well-formed wave down its side (see Figure 4).
At this point the boat is ready for final assembly. Depending on the size of the boat, it may be fitted with cabins, sitting areas, toilets (called heads on boats) and sleeping areas. Electrical lines are hooked up and hoses needed for plumbing (again, on larger boats) are fastened to the boat’s stringers—structural parts that run along the hull.
Catamarans are a popular boat choice for sailors who want to explore shallow bays and other coastal waters. They have two hulls of nearly the same length, which means they can move more quickly than monohulls and also provide a smooth ride in rough seas since their large, flat bottoms minimize the drag of the hull.
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