4.1.1 Wave resistance

Figure 4.1 shows the numerically calculated relative importance of resistance components of a 70 m long catamaran in deep water. The main particulars are presented in Table 4.1. The ship speed U is 40 knots in calm water. The effect of head sea waves with different significant wave heights H _{1 / 3} is also shown. The added resistance due to the incident waves and wind are accounted for by selecting a representative wind velocity and mean wave period for each H _{1 / 3}. Corresponding data for a 70 m long surface effect ship (SES) are shown in Figure 4.2, with the main particulars given in Table 4.2. The ship power is kept constant in the calculations, which means increasing speed loss with increasing H _{1 / 3}. Voluntary speed reduction, for instance, as a result of excessive vertical accelerations, is not accounted for. The speed loss is most pronounced for the SES, as shown in Figure 4.2. The SES speed has dropped from 50 knots in calm water to about 35 knots in H _{1 / 3} = 5m. The speed loss for the catamaran is not shown. However, because viscous frictional resistance is mainly proportional to U ², the...