Experimental Analysis of the Effects of Ventilating behind Transverse Step of High-speed Planning Boats on Reducing of their Resistance Hump

Utilizing transverse steps for high-speed planning hulls is one of the methods for reducing of their resistance and thereafter increasing of their speed. Similar to regular planning hulls, the stepped hulls also have a hump in their resistance-speed curves during the transition from displacement to planning stage. Overcome to the hump usually follows with a heavy load on propulsion systems. In this paper, hydrodynamic characteristics of two planning boat model, a regular V-bottom hull and a hull with one transverse step, are investigated experimentally using towing tank tests. After that the tests for the stepped hull are repeated while a ventilation system is also added behind the transverse step. The results show in preplanning stage, resistance of the stepped hull increased about 30 to 40 percent whereas at the planning stage their resistance reduced about 5 percent respect to the regular planning hull. Using a natural ventilated system for stepped planning hulls reduced both the hump resistance (about 21 percent) and preplanning resistance respect to non-ventilated stepped hull. So, it can be used as a low cost system for practical issues.