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run at speed for a small portion of the route. A hybrid should produce substantially less wake than a
planing monohull or even an SES because the foils generate substantially smaller waves. Our concept
of a passenger ferry for a typical San Francisco Bay Area route as described in Bany and Duffty ( 1999)
is shown in figure 3 above.

10 CONCLUSIONS

The stepped hull hybrid hydrofoil has merits in reduced resistance compared to planing hulls at lower
complexity than pure hydrofoils. It also has merits in seakeeping and other operation areas. Its current
status may be due to being eclipsed by the pure hydrofoil or by problems in takeoff stall, roll
instability or propulsion matching. But it should not be viewed as a partial step to the hydrofoil, and
there are solutions to these other problems. It is a valid concept with its own special characteristics
and capabilities and merits consideration. Hybrid hydrofoils especially merit consideration for high
speed ferry service for partially sheltered runs where seakeeping is a consideration but not an
overriding one, there are factors limiting size on a given run. such as traffk dispersion and moderately
high speeds are required.

Acknowledgments
The authors would like to acknowledge FMC Corporation, the FMC Human Powered Vehicle project.
George Thomas. Bruce Wade, the Cal Sailing Club, Paul Kamen. Kenneth Foster, Michelle Barry and
Ramon S. Villareal for their support in many aspects of this project.

References
Barry C. and Duffty B. (1999). The Stepped Hull Hybrid Hydrofoil. Fast '99. Society of Naval
Architects and Marine Engineers
Blount D. and Codega L. (1992). Dynamic Stability of Planing Boats. Murine Technology. Society of
Naval Architects and Marine Engineers
DuCane. CDR P. M.(1974). High Sped Crafr, David and Charles Ltd.. Devon
Hoemer S. F. (1958). Fluid Dynamic Drag. (Published by the Author)
Karafiath G. ( 1974). An Investigation Into The Performance of NSRDC Model 5 184 Configured as a
Partial Hydrofoil Supported Planing Craft and a Comparison with a Powering Prediction Technique.
Report SPD-585-01. NSRDC
McGhee R. J. and Beasley W. D. (1973). Low-Speed Aerodynamic Characteristics of a 17-Percent-
Thick Airfoil Section Designed for General Aviation Applications. TN 0-7428. NASA.
Martin, M. (1978). Theoretical Determination of Popising Instability of High-speed Planing Boats.
.Journal ofship Researc. Society of Naval Architects and Marine Engineers
Martin M. (1 978). Theoretical Prediction of Motions of High-speed Planing Boats in Waves. Journal of
Ship Research. Society of Naval Architects and Marine Engineers
The views and opinions expressed are those ojthe authors and are not to he construed as official
policy or reflecting the views of the US Coast Guard or the Department of Transportation.