Numerical Analysis of the RAP Characteristics of a Catamaran Vessel for Niger Delta Pliability

摘要

A proper characterization of catamarans performance in relation to demi-hull separation ratio (Sc/L) is imperative for optimal design and applications. Resistance, propulsion and good sea-keeping characteristics for various demi-hull separation ratios at different operating conditions are prime considerations. This work evaluates the Resistance and Propulsion (RAP) characteristics of a 72 m long catamaran for various values of Sc/L (0.3, 0.4 and 0.5). Both physical models and numerical methods are implemented for the analysis. The analysis shows that the frictional resistance (R _( F ) ) of catamaran is parabolic and slightly higher than those of monohulls. However, catamarans have superior sea-keeping performance. The R_( F ) of catamaran dominates the total resistance (R_( T )) at low speeds; however, at high Froude number (Fn > 0.25), wave-making resistance (Rw) becomes dominant, especially during humps. Consequently, the R _(T) -curve and the effective power P _(E) -curve oscillate in rhythm with the Rw-curve as the velocity increases. Again, the effect of residuary resistance interference due to demi-hulls separation ratio is marginal, except during humps. Also, four speed-regimes are identified such as: 1) Low-speed (Fn < 0.23); 2) 1 ~( st ) hump (0.23 < Fn < 0.45); 3) Hollow-wave (0.45 < Fn < 0.60) and 4) 2~( nd ) hump, high-speed (Fn > 0.60). The catamaran P _() _(E) for Fn > 0.6 is very high and uneconomical. Therefore, for optimal performance, catamarans should have service speed limits not exceeding Fn = 0.6.