Experimental and numerical hydrodynamic analysis of a stepped planing hull

Hydrodynamic assessment of planing hulls using overset grids

Numerical investigation of a stepped planing hull in calm water

In this Master Thesis a method to perform resistance predictions on planing hulls with transverse steps has been developed. For hulls without steps there are several methods available to predict their performances. One of the methods is called Savitsky’s method and was published in 1964 and is one of the more famous. Where needed, this method has been modified and used together with other theories to become applicable for stepped hulls. The stepped hull is viewed as two regular hulls following each other closely in the water. The first hull follows the same theory as a normal planing hull since this one meets a calm level water surface. The second hull does however not, as it travels in the wake behind the first hull. Because of this, the shape of the wake has been studied for different conditions like speeds and hull shapes. There are no practical ways to give the shape of the wake as input to Savitsky’s method, but it is possible to interpret the afterbody hull shape relative to the wake surface instead of relative to the level water surface as is usually done, and by doing so view the water as level. Another issue is that it initially is unknown how the weight is distributed between the two hulls, since the two centre of pressures have different positions dependent on speed and positioning of the boat, while centre of gravity of course remains the same. As a solution the author decided to solve the weight distribution by iteration, where suitable start guess that 50-70% of the weight is carried by the forebody is made for most of the conventional hulls with transverse steps. As platform to solve the problem above, MATLAB has been used. A program has been written where the dimensions, weight and speed of the craft are used as input and the new method predicts drag, required power, trim and draft of the stepped hull. The program is tested on a boat with detailed dimensions available. The required power predicted with the program corresponds very well with the available propeller effect at that speed after the air resistance has been added.

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Performance Prediction of Hulls with Transverse Steps

Hydrodynamic study of heeled double-stepped planing hulls using CFD and 2D+T method

Results of an extensive series of model tests that define the longitudinal surface wake profiles aft of prismatic hulls having deadrise angles of 10 o, 20 o and 30 o are presented. Empirical equations are developed that quantitatively define these profiles and are in a form that can be easily applied by designers of stepped planing hulls. These equations are applicable for an expected range of variations in trim angle, speed coefficient, and loading coefficient typical for these hulls. A brief introduction to the concept and to the hydrodynamic advantages of stepped planing hulls is presented to orient the reader as to the importance of wake data in their design. Examples are presented that illustrate the application of these wake data for stepped planing hulls with wetted forebody chine to achieve maximum hydrodynamic lift/drag ratios. Finally experimental results are presented that illustrate the potential resistance penalty associated with the operation of chines dry forebodies where the stagnation line crosses the step.

/pdf/surface-wave-contours-associated-with-the-forebody-wake-of-3ygisp39gl.pdf

Daniel Savistky

Papers

Surface wave contours associated with the forebody wake of stepped planing hulls