In general, motor yachts are built on the same kind of all-purpose modified-V hull forms used in the construction of many
sportfishing boats. A modified-V hull — with its moderate transom deadrise and hard chines — provides a combination of performance, comfort and stability not available with any other configuration. It's a compromise, but a good one.

The difference between a modified-V hull and a semi-displacement hull is oftentimes difficult to distinguish. In general, the semi-displacement design places less emphasis on performance in favor of economical, lower-speed operation. The chines are sometimes softer and a true semi-displacement hull is often narrower of beam than a modified-V design. These hull forms offer little fuss in the transition from displacement speeds to planing speeds, and they can operate efficiently at the transition speeds of a conventional modified-V model. Other semi-displacement designs are trawler-types capable of speeds above hull (displacement) speed but not necessarily in an efficient manner.

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Semi-displacement hulls are most often seen on trawler-style boats (Grand Banks, Albin, Marine Trader, etc.) as well as many of the Downeast designs from New England builders. Seldom capable of 20+ knots top, they provide an economical and comfortable ride at less than motor yacht cruising speeds.

Full displacement hulls are seen only in true trawler designs. A displacent hull is characterized by rounded bilges and deep, full-length keels. Note that a true displacement hull cannot exceed its so-called hull speed which is calculated by multiplying the square root of the hull length by 1.13. The Krogen 42 and Nordhavn 46 are examples of true displacement boats.

Beam is important to us since we want as much interior volume as possible in a boat. Some models we've been aboard recently seem cavernous inside, and their beams were unusually wide. The question is, how much is too much beam?

Although modern production boats clearly have more beam than their predecessors, many yacht designers still consider one foot of beam for each three feet of length close to the ideal length-to-beam ratio for yachts under fifty-five feet. Having said that, the fact is that most modern production boats have beams that exceed that 3:1 ratio. It's not unusual, for example, to see a 36-footer with a 13-foot beam or, say, a 45-footer with a 16-foot beam.