Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014


Figure 15. Sternpost angle definition


Table 4: Effect of variation in sternpost angle on change in trim of stepped hull Step Height


Sternpost Angle


0.7 1.4 2.2 2.9


Change in Trim (Degrees)


% Beam Degrees CV = 1.5


0 0 - 1.42 2.85 4.29 5.71


0.3 0.6 1.0 1.3


CV = 2.9


-


0.2 0.4 1.5 2.8


CV = 4.6


-


0.1 1.0 1.4 2.2


this study (no step in the hull, or a step so large that the afterbody is not wetted). Between these two extremes, when there is afterbody


wetting, large bow-down


pitching moments can be created and the standard Savitsky method will not apply. The paper by Savitsky and Morabito (2010) addresses this in detail.


Figure 17: Effect of trim angle on resistance-to-weight ratio of stepped hull


Figure 16: Effect of variation in sternpost angle on change in trim of stepped hull


Lawrence Doctors also inquired about the applicability of the Savitsky method to the data in this paper. Savitsky method will only be valid at the endpoints of


B-122 The


It is interesting to compare the general trends of stepped hull resistance with that of unstepped hulls. Figure 17 was created by cross-plotting the data in the paper, to compare with Figure 16 of Savitsky’s 1964 paper. The results of these model tests are in agreement with the trends of unstepped planing hulls, where at low trim angles there is a large component of viscous drag. At high trim angles the dominant component is pressure drag.


©2014: The Royal Institution of Naval Architects


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88