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forces similar to those reported by Blount and Codega (1992) originating in the curved bow sections
forward. Based on this, the authors are convinced that the preferred hull form is in fact essentially a
“three point catamaran” comprising two slender hulls forward and the foil aft between the extension of
the centerline of the hulls. The other point should have been obvious upon retrospection, but became
evident when some models either failed to lift or lifted only with great difficulty (their announcement
of takeoff was accompanied by a radical change in the engine sound which was the clue): The
propeller is very heavily loaded at the low takeoff speed as it is operating at much lower advance ratio
than the propulsion system is optimized for. This can prevent the engine from achieving full power
when it is most needed.

Figure 3 Stepped Hull Hybrid Hydrofoil Catamaran Ferry Concept
Any practical hybrid will have to have a propulsion system that will not overload the engine in the
takeoff condition. This can be achieved by two speed gearboxes (which have recently become
available), surface piercing drives forcibly ventilated by propulsion machinery exhaust or by use of jet
drives, which have other advantages as well.

9 HYBRID HYDROFOIL FERRIES
A high speed ferry is one obvious applications for the hybrid hydrofoil stepped hull concept. A ferry is
a single speed vehicle, and the hybrid concept is well suited for this. Most practical new ferry routes
in require a speed on the order of thirty to forty knots to compete with automobiles provided the speed
can be achieved at an acceptable level of cost and reliability. This appears to be the optimum range for
this concept, so a stepped hybrid may be able to achieve a lower cost and better reliability at these
speeds than hydrofoils, SES‘s, or planing boats. The stepped hybrid concept is much less dependent on
size for speed and seakeeping than a conventional planing hull, so smaller, less expensive femes are
feasible. This allows either more ferries on a given run or use of ferries for runs with much less traffic.
A number of high speed ferries are limited by wake damage to the shore. As a result, they can only