Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014
Dr Dean Schleicher has brought up concerns that were not
intentionally kept small to demonstrate the primary effects of an aft step (or a hydrodynamic
addressed in the paper, including variations in loading condition, seakeeping and stability.
directional
This particular set of tests has been transom
forward of the geometric transom) on the resistance and trim of a planing boat. The paper provides a simple procedure to determine when this concept would be expected to reduce resistance. The step location of 25% LOA forward of the transom was chosen for illustrative purpose and because of the availability of the model. We do not advocate building a full-scale boat on these lines.
Rather we hope that this paper generates some interest and more understanding of the concept.
Recent towing tests on stepped planing hulls, carried out by Dr. Gregory White and William Beaver and presented at the 2012 Chesapeake
Power Boat Symposium
demonstrated the effect of rough-water on the resistance and impact accelerations of stepped planing hulls. These studies showed that while the resistance was reduced by incorporating a step, the vertical accelerations were increased.
This increase was primarily the result of
increased running trim. We have not yet run the model discussed in this paper in a seastate, but we would expect similar results.
Over the past two years, we have been studying the directional stability of stepped planing hulls, including one of the aft-step configurations
discussed in this
paper. Some of these studies have been summarized in a paper written by us for the 2014 Chesapeake Power Boat Symposium. This model is directionally stable; however our tests with it and other models show that we are far from a predictive methodology. We have found that in general, steps have a
very small destabilizing
effect. However, differences in hull geometry such as length, beam, deadrise and bow shape seem to have a much greater influence on directional stability.
REFERENCES
8. BLOUNT, DONALD L and CODEGA, LOUIS T. “Dynamic Stability of
Planing Boats,” Marine Technology, January 1992.
9. SAVITSKY D and ROSS E, “Turbulence Stimulation in the Boundary Layer of Planing Surfaces,” Stevens Institute of Technology, Davidson Laboratory Report 444, August 1952.
10. MORABITO, M.G., PAVKOV, M., TIMMINS, C., BEAVER, W. Experiments on Directional Stability of Stepped Planing Hulls. The Chesapeake
Power 11. WHITE, G., Boat Symposium.
Annapolis, Maryland, US, May 2014 and
BEAVER, W., An Expermental Analysis of the Effects of Steps on
a High Speed Planing Boat. Chesapeake Power Boat Symposium, Annapolis, Maryland, US 2012.
©2014: The Royal Institution of Naval Architects
B-123
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