A discussion of the design pressures appropriate to the bottom of a planing boat

• Published in: Ocean engineering 1988, Vol.15 (5), p.471-493
• Main Author: Payne, Peter R.
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Ground, air and sea transportation, marine construction; Marine; Marine construction
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/0029-8018(88)90011-X

In designing the structure of a high-speed planing boat, it is obviously desirable to know what to use as a “design pressure”. Eight papers in the literature present methods of doing this, but the “answers” they give are in wild disagreement. At 60 knots, for example, the lowest recommended design pressure is 7 lb in. −2 and the highest is just ten times that figure. In this paper, the pressures which occur on a prismatic planing hull when it impacts on a flat water surface at an arbitrary speed and trim angle have been calculated. The results have little resemblance to any of the eight empirical approaches. The actual pressures are much lower at normal trim angles and far higher at the large trim angles often experienced in the exuberant operation of pleasure boats in moderately rough conditions. But the peak pressures and forces are over so quickly that there is no possibility of “rigid boat” strains building up in the hull structure, so the concept of an “equivalent design pressure” has no meaning. It is rather a question of whether the relative kinetic energy of the boat just prior to impact can be subsequently accommodated by the structure as strain energy without failure. With this in mind, some simple strain energy calculations show that a fiberglass hull can be two orders of magnitude “stronger” than a steel hull if it is important to avoid yield deformation.