A cathedral hull is a hull shape used in modern boats, usually power-driven. It can be thought of as a kind of vestigial trimaran in which the center hull has two smaller side hulls which are so close to the main hull that there is no longer any open space. In fact a cathedral hull is a vee-bottomed boat with side skirts which extend almost as far forward as the main hull. The airspace between the hulls may be very small or nonexistent--a good example would be the classic "Boston Whaler 13" which is nearly a flat-bottomed scow at the stern.
Depending on the proportions of the side skirts and the depth of the main hull, the cathedral hull can approach the handling characteristics of either the Hickman sea sled, or the deep-vee hull. (Worth noting is that the naval architect first credited with the successful use of the deep-vee hullform, C. Raymond Hunt, also invented the Boston Whaler).
The term "cathedral hull" refers to the resemblance of a section through an inverted boat to that of a medieval cathedral.
The cathedral hull configuration tends to result in a very broad bow; many such boats are completely rectangular. This provides the maximum cargo or working space for a given length and beam. The hull shape is also very stable compared to a conventional v-shaped bottom, and in either light chop conditions or above 40 knots or so is faster than a flat bottom, for the same weight, length and beam.
Cathedral hulls became popular in the 1960s and 1970s, when the use of fiberglass made economical production of this hull-form possible. The undesirable aspects of the cathedral hull are greater weight and cost, pounding in rough water, and a boxy appearance. Their advantages include high waterplane area at rest (good initial stability) a dry ride in light chop, and reasonable fuel economy at planing speeds. In exposed waters this hullform has been almost totally replaced by the modified-vee and dee-vee hull-forms. After a period of reduced popularity, they live on in modified form as "deck boats" which are very popular in the inland lakes and rivers, especially in the south and midwest.