Experimental study of the effect of velocity on dynamic trim, as a measure of the occurrence of longitudinal instability in a planing boat example using sea trial tests.

One of the undesirable phenomena in the achievement of planing vessels at high speeds is the phenomenon of longitudinal instability. This phenomenon, which is in fact an unstable coupling between heave and pitch, causes damage to the vessel, equipment and crew. In order to evaluate and accurately calculate the speed of occurrence of this phenomenon in the design stages, it is necessary to perform numerical analysis or model testing. Therefore, the existence of a valid data set to validate these analyzes, especially numerical analysis is essential.In this paper, by setting the dynamic trim as a criterion for the occurrence of porpoising in a planing boat, the amount of this trim at different speeds is measured on a sample of a cougar boat without steps in the sea. These results show that the dynamic trim has an increasing trend with increasing speed and after the float is in planing mode, it gradually decreases and tends to an almost constant value at high speeds.