In this appendix the results of the slender body resistance prediction method have been compared against model test data for the following hull forms:
Results for the simple Wigley hull form are given below. Here results are compared with two theoretical methods Insel (1990) and Michlet as well as experimental results from Insel (1990). Hullspeed can be seen to be in close agreement with the other two analytical methods. Although there is a reasonable amount of scatter in the experimental results, it appears that the theoretical methods tend to over-predict the wave resistance. In the case of the experiments, the model was held fixed in trim and sinkage, i.e. the model was kept at the datum waterline.
Wigley parabolic hull parameters:
L/B 10.0
B/T 1.6
CB 0.44
CP 0.44
CM 0.44
WSA/L2 0.1488
Monohull:
Wigley hull bodyplan
Comparison of results for Wigley hull
Catamaran: centreline separation / length = 0.2
Comparison of results for Wigley catamaran
Trimaran: ama half main hull dimensions
Comparison of results for Wigley trimaran
The following graph shows a comparison between results from Hullspeed, other theoretical methods and experimental results for a transom-sterned hullform. The model is a stretched NPL round-bilge form. For transom-sterned hulls, Hullspeed adds a “virtual appendage” which models the air-gap behind the transom when the water releases cleanly from the transom edge (high-speed condition) and the turbulent viscous wake behind the transom at slow speed (low speed condition) – this method is described in detail in Couser et al (1996). For these experimental results the model was free to sink and trim; the theoretical results of Couser et al (1996) included the actual running trim and sinkage as measured during the experiments and hence the very close agreement with the experimental results. The results for Hullspeed use a fixed waterline, since, in general, the trim and sinkage condition at each speed is not known. The results from Michlet use a different method for dealing with the transom. The results from Hullspeed show good agreement with the experimental results, particularly when the transom is clearly in the high or low speed condition; in the transition condition, around Froude number = 0.5, Hullspeed under-predicts the resistance.
NPL round bilge, mode 4a (Couser et al 1996 notation) hull parameters
L/B 10.4
B/T 1.5
CB 0.397
CP 0.693
CM 0.565
WSA/L2 0.1359
NPL (model 4a) hull bodyplan
Monohull:
Comparison of results for NPL (model 4a) hull - monohull
Catamaran: centreline separation / length = 0.2
Comparison of results for NPL (model 4a) - catamaran S/L = 0.2