Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014
At the start of the test, there were a series of questions that the authors aimed to answer. The following answers pertain to the hull tested. Further research is necessary to extend these findings for generalized hulls.
What is the effect of an aft step on resistance and trim at high speeds?
25% reduction at Cv = 4
How does step height influence resistance and trim?
The largest step height tested increased trim at hump speed by nearly 50%.
The effects What is the resistance penalty at low speeds?
10% increase at Cv = 2
How do steps affect the porpoising stability of planing craft?
Observations seem to agree with monohull porpoising stability limits; however more tests need to be conducted in the unstable regime. The step height has a critical effect on porpoising stability because too large a step will result in a high trim angle that causes porpoising.
As
speeds increase, the lift coefficient decreases and the porpoising trim angle is reduced. When the critical trim angle is less than the optimum trim angle of 4-degrees, it is not possible to achieve minimum resistance, and a compromise must be made between longitudinal stability and resistance.
The present study indicates that this configuration of stepped hull may be an attractive design choice, and should be considered as a potential alternative in early design stages of future special operations craft.
5. ACKNOWLEDGEMENTS
The authors would like to thank Dr. Gregory White at United States Hydromechanics Laboratory for the use of the towing facilities and Evan Lee of the Naval Surface Warfare Combatant Craft Division for the use of the stepped hull model.
6. REFERENCES
1. CLEMENT, E.P. and POPE, J.D., Stepless and Stepped Planing Hulls – Graphs for Performance Prediction and Design, David Taylor Model Basin – Hydromechanics Laboratory Research and Development Report No. 1490. January, 1961.
©2014: The Royal Institution of Naval Architects B-95 diminished with
diminishing step height. Step heights from 2.85 – 5.71% b had similar resistance at the high speeds
3. WHITE, G.,
2. SAVITSKY, D., and MORABITO, M., Surface Wave Contours Associated With the Forebody Wake of Stepped Planing Hulls, Marine Technology, Volume 47, 2010. and
BEAVER, W., An
Experimental Analysis of the Effects of Steps on a High Speed Planing Boat, Chesapeake Power Boat Symposium, Annapolis, Maryland, USA, 2012
4. MATVEEV, K., Hydrodynamics of Tandem Planing Surfaces, Transactions, Society of Naval Architects and Marine Engineers, 2013.
5. LEE, E., and PAVKOV, M., The Systematic Variation of
Step Configuration and
Displacement for a Double Step Planing Craft, Journal of Ship Production and Design, Vol. 30 No. 2. May, 2014.
6. SAVITSKY, D., Hydrodynamic Design of Planing Hulls, Marine Technology, Volume 1, No. 1, 1964.
7. LEWANDOWSKI, E.M., The Dynamics of Marine Craft: Maneuvering and Seakeeping, World Scientific Advanced Series on Ocean Engineering – Volume 22. 2004, 2008.
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