Experimental measurements of hull pressures on fast displacement catamarans during motions in long-crested head-seas

Piezoresistive pressure transducers have been used to measure the pressure variations at six points on a catamaran hull moving in regular, long-crested, head-seas. Preliminary results demonstrate the feasibility of this experimental approach although a more refined experimental procedure may be required to obtain greater accuracy in the pressure measurements.The pressure measurements were carried out for one demihull spacing at two speeds in calm water and also in regular waves of differing wave periods. The mean pressures from both calm water and regular wave tests are presented along with the RMS variation from the mean during the tests in regular waves

Experimental measurements of the seakeeping characteristics of fast displacement catamarans in long-crested head-seas

The report describes an experimental investigation into the seakeeping properties of catamarans. Three geometrically similar hull forms were tested covering a range of Length:Displacement ratio from 7.4 to 9.5. The hulls are of round bilge transom stern form and are based on the NPL round bilge series. A number of hull configurations, including monohull and two catamaran demihull spacings, were tested at three Froude numbers (F subscript n = 0.2, 0.53, 0.8) and over a range of wavelengths. Long-crested head-seas were used for all experiments. Measurements of heave, pitch, vertical acceleration at two stations and added resistance in waves were made. Response functions have been calculated from both regular and irregular wave experiments

Theoretical prediction of the seakeeping characteristics of fast displacement catamarans

The increase in the number of high speed craft of all types operating throughout the world that has been seen over the last decade is continuing. With this likely to remain so for the foreseeable future, there is considerable interest in being able to predict the motions of such vessels in a seaway with accuracy.This report employs both two-dimensional and three-dimensional potential flow analyses to evaluate the hydrodynamic coefficients and responses of high speed displacement catamaran forms. The hullform is based on the NPL round-bilge series, and is considered in three configurations; as a monohull and two catamaran demihull spacings. These hull configurations were investigated in regular head waves at three different forward speeds, corresponding to Froude numbers of 0.2, 0.53 and 0.8.Hydrodynamic coefficients and heave and pitch responses are presented for all of the configurations examined. Comparisons with experimental data are included and discussed. For one of the catamaran configurations comparisons of pressure measurements at points around the hull are also presented.The limitations of the theoretical models used are discussed with reference to: a) their treatment of forward speed effects,b) viscous damping effects around the resonant responses,c) the effects of changes in hull attitude with forward speed,d) the modelling of a transom stern, particularly at higher speeds

Theoretical prediction of the seakeeping characteristics of two fast displacement catamarans in oblique seas

This report employs two different three-dimensional potential flow analyses to evaluate the hydrodynamic coefficients and responses of two high speed displacement catamaran forms. The hullforms are based on the NPL round-bilge series and the Series 64 form. For each hullform two catamaran demihull spacings are considered. These configurations are investigated in regular deep water waves at three different heading angles; namely head seas (? = 180°), ? = 150° and ? = 120°, and for a forward speed corresponding to a Froude number of 0.65.A selection of hydrodynamic coefficients are presented, together with heave, pitch and roll responses for all of the configurations examined. Comparisons with experimental measurements are included and discussed. Differences between the two three-dimensional methods are discussed and the limitations of the current theoretical methods highlighted. Possible ways to improve the theoretical models are outlined with particular reference to: a) the treatment of forward speed effects,b) viscous damping effects around the resonant frequencies,c) the effects of changes in hull attitude with forward speed,d) the modelling of a transom stern, particularly at high forward speeds