In this study, a high-speed planing trimaran hull form is designed, and the effects of different displacements and gravity longitudinal layouts on the performance of the trimaran planing hull in calm water are experimentally investigated in the towing tank of the China Special Vehicle Research Institute. Based on previous work, an innovative inner tunnel appendage hydroflap is mounted in the inner aft tunnel, located 1/8 L from the transom in the longitudinal direction with attack angles of 0° and 4°, respectively. Furthermore, a regular stern flap is mounted on the transom close to the chine. The towing test results show that, as the gravity center moves forward, the high-speed region resistance of the planing trimaran increases and the longitudinal stability is also strengthened. Further, the total resistance of the planing trimaran with a heavier displacement is larger while the average mass resistance declines; i.e., the resistance efficiency is improved. The results also indicate that the inner tunnel hydroflap and stern flap enhance the aft hull hydrodynamic lift and tunnel aerodynamic lift. As a result, mounting aft hull lift enhancement appendages can affect the bottom and inner tunnel pressure distribution and then cause a slight resistance decrease in the low-speed region. The value relationship of resistance between groups of appendages for the attached hull and bare hull is reversed at a speed of about Froude number 3.0. Although the aft hull lift enhancement appendages result in a higher resistance cost in the high-speed region, the longitudinal stability is effectively promoted and the occurrence speed of porpoising results in a delay of 1 to 2 m/s.

When the planing hull is sailing at high speed, the proportion of air resistance to the total resistance increases significantly. Therefore, by studying the aerodynamic characteristics of the planing hull shape, we can analyze the influence of the hull shape on the aerodynamic performance of the planing hull, and find a method to reduce the proportion of air resistance. The research took the planing trimaran as the research object, completed the wind tunnel test, and established the numerical simulation method by solving the RANS equation and combining the k-ε turbulence model. Combined with the wind tunnel test data, the calculation accuracy of the computational fluid dynamics (CFD) method was judged. Then, four superstructure shapes and two tail shapes were simulated by the CFD method, and the characteristics of the air resistance and airflow field of several drag reduction schemes with a volume Froude number between 7.00–17.51 were analyzed. The research focuses on the aerodynamic force of the planing hull. The results show that the circular arc stern has a more obvious drag reduction effect than the square stern, and the streamlined mid-arched superstructure has certain advantages in the drag reduction effect.

Porpoising is defined as unstable coupled heave and pitch motions. In this study, seven test conditions with various longitudinal locations of the center of gravity and the moment of inertia were designed to study the porpoising phenomenon of a tunnel-type planing trimaran. After comparing the lower speed limit for porpoising, this study revealed that moving the center of gravity forward could increase the lower speed limit of porpoising, but it could also increase the amplitude of heave and pitch. Furthermore, the reduction of the moment of inertia of the planing hulls could effectively reduce the oscillation amplitude of planing trimaran porpoising and improve the longitudinal stability of planing trimarans. In this test, condition A5 had a 15% reduction in the inertia moment compared to A3, but the amplitude of the pitch oscillation in porpoising decreased by 60%. Unlike conventional trimaran towing tests, this experiment studied the effect of speed on porpoising after exceeding the lower speed limit for porpoising and found that with an increase in speed, the amplitude of porpoising first increased, then decreased, and then increased again. This study defines the speed at which the amplitude of porpoising increases for the second time as the second critical speed of porpoising. The porpoising generated by a planing trimaran after reaching the second critical speed is defined as the second porpoising. Finally, the limitations of the conventional longitudinal stability limit curve method to predict the porpoising of a planing trimaran are discussed.

No abstract