Early HysucraftTM Design Process
Early HysucraftTM were designed by use of planing craft data and the hydrofoil formulations were derived from aeronautics similar to those by E.V. Lewis. The final craft was then optimized in systematical model tests. Several efficient HysucraftTM were built.
For further optimization more theoretical knowledge was needed to understand the hull-foil interference better and this lead to the development of the advanced mathematical model.
Without the use of the advanced mathematical model, one risks re-inventing the wheel at substantial costs and risks of failure. As can be seen below, ensuring that a vessel has the inherent stability and strength takes much more than thumb sucking and trail and error, many market participants fail to realize this key aspect.
FASTcc’s Proprietary Advanced Mathematical Models and Computer Software
In order to efficiency develop a HysucraftTM a computer program to determine the hydrodynamic characteristics of the HysucraftTM was developed with additional programs for hydrofoil strength and hull stability calculations.
The planing hull hydrodynamics are determined by use of the well-known Savitsky formulations and the E.V. Lewis, which were developed for prismatic deep-V-planing hulls and are based upon many systematical model test results. The semi-empirical methods allow the lift-drag forces and center of pressures to be determined in relation to the trim, dead-rise angle, wetted lenge and beam.
The catamaran is considered a deep-V-hull split along the center plane and set apart to form the tunnel with straight flat walls between the demi-hulls. Wetted tunnel areas are included. The hulls are first analysed in a fixed position and the planing lift-and-drag forces as well as their moments are determined. The hydrofoils are then considered wit their relative positions to the hulls and to the water level.
Hydrofoil lift, drag and their moments (to transom) are calculated corresponding to the hydrofoil theory for optimal lift distribution (elliptical) corrected for surface mode by use of an empirical correction derived in systematical towing tank tests.
Confirmed by Semi-Empirical Tests
The effective aspect ratio of the foils is determined and incorporated in the lift and drag calculations. Plan form correction from Silverstein and a sweep correction as indicated by E.V. Lewis are added.
The trim-foils in the wake of the main-foil are determined for the corresponding inclined inflow, which results in lower efficiencies. For cavitation check the cavitation index by D. Cane is determined and printed out. Additional elements as spray rails, keel-beams, stern-wedges or transom flats, air-flit of the tunnel ceiling, foil middle strut lift and drag with interference, and the air drag are determined, mainly by use of formulations derived from Hoerner. The corresponding moments over transom are calculated.
The initial demi-hull forces are then corrected for the foil-on-hull interference, which results in increased planing forces. All vertical force components are summarized and put into relation to the craft weight force vector, that has to balance the forces. First there will be no equilibrium of vertical forces and a new draft is interpolated for. Successive iterations give the draft for which vertical force equilibrium is reached. Similar iterative calculations with the force moments and trim angle variation results in the floating trim angle determination.
This also includes the propulsor thrust line. Calculations can be repeated for desired speeds, loads and LCG positions of a design proposal. The calculations are controlled by a set of input data. The HysucraftTM can reach dynamic instability when foils periodically penetrate the water’s surface and a porpoising action is observed. The iteration process is then interrupted and no equilibrium position is achievable (endless computation). A counter variable has to stop the program and the design-input data has to be verified for new computations.
All design and hydrodynamic parameters are given in a printout for design revisions. By systematical design parameter variation the minimum effective power is reached which indicates the optimum combination. However, aspects of practical construction, sea-keeping, course holding, turning characteristics and stability at all speeds are kept in mind and may limit the choice of input parameters.
The final total resistance is further corrected for speeds around the so-called hump resistance where the planing effects start to bear by a method shown as shown by Blount et al as the Savistsky formulations are known to under-predict the resistance in this speed range.
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