Design of a high speed planing hull with a cambered step and surface piercing hydrofoils

Abstract

Design of a high speed planing hull is analyzed by implementing a cambered step and stem, surface piercing hydrofoils, commonly known as a Dynaplane hull. This configuration combines the drag reduction benefits of a stepped hull with a fully ventilated after body by using a stem stabilizer. The largest obstacle with this design is maintaining trim control and stability at high speeds. There has been limited research on the Dynaplane design since Eugene Clement first conducted tow tank tests in the David Taylor Model Basin (DTMB) in the 1960s. Modem experimental methods such as computational fluid dynamics (CFD) allow the designer to run multiple simulations at once while testing a variety of parametric variables. The analysis will combine theoretical, empirical, and computational methods to determine the hydrodynamic characteristics of the design and develop a new Dynaplane configuration that allows for speeds in excess of 50 knots. The design approach begins with using a reference hull named Model 5631 from a small systematic series of resistance tests at the DTMB. This modeled hull is based on the U.S. Coast Guard 47 ft Motor Lifeboat which is a hard chine, deep V planing hull. Clement's Dynaplane design process was followed with exception of the stem stabilizer recommendation. Instead, a surface piercing super cavitating (SPSC) hydrofoil designed by Dr. Stefano Brizzolara was used. These designs further improve upon the powering requirements of a conventional planing hull by effectively increasing the lift to drag ratio. A commercially available CFD software program called Star-CCM+ is used for the computational portion. The computational model is first validated using results from the Model 5631 tow tank tests. Three series of CFD tests were then conducted on the new Dynaplane design; which include developing wake geometry predictions for a swept back stepped hull, and then varying the trim angle and longitudinal center of gravity. These tests were run at an FnV=5 in a calm sea state. Results from the analysis demonstrate the benefits of a fully ventilated afterbody using the SPSC hydrofoils and predict the hydrodynamic behavior for the new design. Also, the results extend the range of application of Clement's Dynaplane design to hulls with 20 degree deadrise. This thesis gives naval architects design guidance for such a hullform and demonstrates the potential of CFD as a tool for analyzing these parametric variables.