Model testing and computational analysis of a high speed planing hull with cambered planing surface and surface piercing hydrofoils

Abstract

As part of a 2014 thesis, the MIT Innovative Ship Laboratory (iShip) designed a high-speed planing hull form that was based on the Model Variant 5631 developed at the US Navy's David Taylor Model Basin [7] [3] [5]. This model was a variant of the parent hull 5628. The 5631 variant was a model of the 47 foot Motor Lifeboat of the US Coast Guard, which was a hard chine, deep-vee vessel. Model 5631 had no step, with a 20 degree dead rise angle. The Clement method [4] was used in order to design a cambered planing surface that would generate dynamic lift and support most of the weight of the vessel. A second cambered step was designed using an in-house lifting surface program. The step was designed such that, at top speed, the entire hull aft of the step would be ventilated. To accommodate this effect, the aft underbody design departed from the conventional dead-rise. Directional stability of the model in the pre-planing regime was increased by incorporating three vertices at the design dead-rise angle. A set of super-cavitating, surface-piercing hydrofoils were designed to be attached aft of the vessel transom in order to provide support and prevent re-wetting of the afterbody. The constructed hydrofoils were positioned in a vee configuration, differing from the anhedral design in the Faison thesis. A support manual control system for the hydrofoils was designed as part of this thesis. Known as Model 5631D, this dynaplane model underwent a series of tests at the 380 foot towing tank at the United States Naval Academy in Annapolis, Maryland, over the course of several days. Several parameters were varied during the tests: the cambered step (via the wedge insert), the carriage speed, and the model longitudinal center of gravity (LCG). In this thesis, data from the series of tests of Model 5631D will be compared to that of the tests of Model 5631 by combining methods from Savitsky [15] and Faltinsen [8] for data scaling of planing vessels. Both models were scaled to the same static waterline length in order to determine the efficacy of the new design changes of Model 5631D in reducing total drag. Additionally, comparisons of the test data were made to computational fluid dynamics models conducted under the same conditions in the virtual environment. An introduction and motivation for the thesis is presented in Chapter 1. Half and full factorial statistical analysis was performed on the testing data and presented in Chapter 2, along with the results of data scaling and comparison of Hull 5631D's performance to the parent hull. Results of the CFD simulations along with calculation of model stability is presented in Chapter 3. Conclusions and opportunities for future work are given in Chapter 4. A full catalogue of the testing data is given in Appendix A.