Dart 38 (11 m), a recipe for “flying” at 76 knots in the early 1970s

Genoa, 1972. Anyone who was at the Boat Show that year might remember an iconic hull, not quite a Classic Boat, but certainly a classic of Italian boating: the Dart 38, Renato “Sonny” Levi‘s 76-knot, 1,000-horsepower offshore boat. In essence, the fastest boat of its time.

Dart 38, a 76-knot bolide

It all stemmed from a meeting with Eng. Carlo Chiti -reports in a ’72 article by Levi himself- world-famous designer both for his racing cars for Ferrari, then for Alfa Romeo. It was during Chiti’s tenure at Autodelta that the idea was born, when he informed Levi of an engine so successful that it would also be ideal for an offshore. In a nutshell, it is a pair of Alfa Romeo engines derived from the 33 Stradale of the same name, transformed from the original 2 liters to 4 liters, from 250 horsepower to 500… It will be one of the most powerful engines and, on Levi’s Dart 38, will equate to a total of 16 cylinders to fly at 76 knots.

Dart 38 – Hull and design

Looking at pure technique, the hull is a deep V with an aft dihedral of about 25° and extremely narrow beam, for a beam-to-overall length ratio of just 1/8. The hull is, in short, a kind of splinter, a dart in fact (dart, dart in English), 11.25 meters long and just 2.75 meters wide. A subspecies of missile capable of running over 140 km/h on water–an achievement as impressive as it is complex to achieve.

In fact, the starting point, once in possession of the engines, was hydrodynamic reduction, which was essential in order to bring out the maximum horsepower offered by the engines. Keeping in mind that propellers and the axles themselves are a huge source of hydrodynamic resistance, Levi was able to solve here with a stroke of genius: surface propellers. That is, moving from a traditional shaft-line system with submerged propellers to a surface system simultaneously reduces both the friction produced by the axles (they have less inclination and therefore less resistance) and that given by the blades themselves, which, here, instead of creating drag in their non-thrust phase, are out of the water, cancelling the resistance. At the same time, the serious problem of cavitation* is avoided.

To further improve strength and trim, the two Alfa Romeo engines were installed offset in height and one in front of the other, thus reducing the beam and better distributing the weights, while decreasing the transverse distance between the two axle lines. Further aft on the deck was then located the wheelhouse station. In terms of gliding surfaces, however, two skids helped to distribute the lift of the areas.

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The meeting of hydrodynamics and aerodynamics

Speaking of a hull capable of this performance, the aerodynamic aspect also becomes crucial, a priority so that the efforts aimed at the design of the living work are not wasted, as well as so that the stability of the hull itself is not affected. Notable in this case are two side fins, positive dihedral half-wings designed by Levi to simultaneously improve lateral aerodynamic and hydrodynamic stability, thus arresting the roll that might occur at high speeds.

A useful quality even in the event of a capsize (it happens to offshoreers, sinking into the waves or literally flying through the air), since the shape of them was designed to straighten the hull as well, returning it, if nothing else, to a normal position.

Operational Life

Impressive as it was, as well as actually fast and functional, the Dart 38 had a short and unfortunate life. If in the first trials he proved to be monstrously efficient and fast, perhaps the fastest of his time, once they reached the race courses luck and music changed.

In 1973 he had to retire already in his first race, instead going seriously damaged in the second. Here, due to an accident that prevented the co-pilot’s participation, he raced with the driver alone, but paid the price of a significant weight difference from the design. Detail that, if with the wave in the bow caused no difference, saw him instead sinking into a wave in passing it running in his own direction. Needless to say, water entered the air intakes and backgrounded everything, marking the abandonment of the project and the subsequent demolition of the hull. An experience that, while seemingly unsuccessful, would instead mark the future of boating, which today sees so many of the ingenious solutions introduced here by Levi introduced.

Dart 38 – Data Sheet

*Cavitation (for short): the creation, in the vacuum face of the blades, of a vacuum, that is, a depression capable of causing water to pass from the liquid to the gaseous state with rarefied vapor bubbles. The risk, in addition to reduced propeller efficiency, is propeller idling, as well as the potential implosion of bubbles, capable of damaging the blades.

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Questa piccola meraviglia è il Rio Espera (6.9 m), il primo Rio di sempre – Classic Boats