Page 144 - Practical Design Ships and Floating Structures

Practical Design of Ships and Other Floating Structures 119
You-Sheng Wu, Wei-Cheng Cui and Guo-Jun Zhou (Eds)
8 2001 Elsevier Scicncc Ltd. All rights reserved

THE HYBRID HYDROFOIL STEPPED HULL

Bryan Duffty and Christopher D. Barry

Fast Hulls, hc., 3020 Daurine Ct, Gilroy, CA 95020 USA
USCG ELC-024.2401 Hawkins Pt. Rd. Baltimore MD 21226 USA

ABSTRACT

Planing hybrid hydrofoils or partially hydrofoil supported planing boats are hydrofoils that
intentionally operate in what would be the take off condition for normal hydrofoils. They offer a
performance and cost that would be appropriate for some femes, light cargo and recreational vessels.
The stepped hybrid hydrofoil configuration made its appearance in the high speed boat scene in the
late nineteen thirties, but never was widely used. It is a solution to the problems of instability and
inefficiency that has limited other type of hybrids. The purpose of this paper is to reintroduce this
concept to the marine community while proposing what the authors believe address the problems that
initially limited this concept.

KEYWORDS
Hydrofoil, Hybrid Hydrofoil, Partially Supported Hydrofoil, Stepped Hull

1 BACKGROUND
A hybrid hydrofoil is a vehicle combining the dynamic lift of hydrofoils with a significant amount of
lift from some other source, generally planing lift. The attraction of hybrid hydrofoils is the desire to
meld the advantages of two technologies in an attempt to gain a synthesis that is better than either one
alone. Partially hydrofoil supported hulls mix hydrofoil support and planing lift. The most obvious
version of this concept is a planing hull with a hydrofoil more or less under the center of gravity.
Karafiath (1 974) studied this concept with a conventional patrol boat model and a hydrofoil. His
studies revealed many configurations were unstable in pitch. The subject of this paper is a particular
configuration of partially hydrofoil supported planing hull that addresses the pitch instability issue.
The authors initially became involved with the hybrid concept when working on FMC’s High
Waterspeed Test Bed (HWSTB) for the US Marine Corps, which was a hybrid with an aft hydrofoil
and a forward planing surface. The HWTB project is beyond the scope of this paper, but the concept
worked. A half scale demonstrator representing a 66,000 Ib. armored vehicle made 35 knots true
speed. The authors independently developed the stepped hull concept from this system before
discovering that it was previously developed and actually in service, but for some reason, never found
a niche and has disappeared. This paper is intended to reintroduce the hybrid hydrofoil concept to the
marine industry and to provide some inspiration to others. We believe that there were critical issues