Wave Height and Planing Hull Wave Slams in Regular Waves

Abstract

High-speed planing boats are subject to repeated slamming impacts. These impacts can cause structural damage and discomfort, or even injury, to passengers. The motivation for this research is to determine a relationship between wave height and vertical accelerations of planing crafts. A series of towed-scale model experiments was conducted in regular waves to capture a sequence of individual impact events. The experiments were conducted in a 380-foot long, 26-foot wide, and 16-foot deep tow tank at the US Naval Academy. Two model scales of the same geometry were tested at different Froude numbers and over regular waves with different wave heights. Wave height was varied using two methods. The first method was to keep the wavelength constant and increase the wave height. This produced waves with a larger wave slope, as well as the larger wave height. The second method was to keep the wave slope constant, thus increasing the wavelength along with the wave height. Vertical accelerations were measured at three locations (the LCG, the bow near the FP, and a point between the bow and LCG). Each wave encounter was treated as an individual slam event. The acceleration time histories were separated into individual impacts. All impacts show a general shape. There is strong agreement in the overall shape of the impact event. The peak vertical accelerations depend on the ratio of wave height to boat length squared, the square-root of the wave slope, and the boat speed squared. This paper will explain the methodology for separating impacts in regular waves as well as the scaling relationships for peak acceleration magnitudes and full acceleration impact time histories.