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Introducing

Tuna Drive

Is this the next breakthrough in
pod propulsion or a fishy story?

By Chuck and Lawrence Husick

Hydraulic rams powering the segmented “tail” sections allow the prototype Tuna Drive to deliver theoretical speeds of 35 knots.

Pod drives have revolutionized the technology of powerboat propulsion. The combination of horizontal propshaft angle, contra-rotating propellers and vectored thrust yield higher speed, greater maneuverability and significantly improved fuel economy, along with a significant reduction in noise and exhaust. The benefits of these drive systems, however, will soon be eclipsed by the new Propulsione di Tonno Coda (PTC) drive system being introduced by Scioccodiaprile, AG of Modena, Italy.
The new PTC drive resembles the IPS, Zeus and POD systems in its use of a controllable azimuth drive pod below the hull of the boat. However, the PTC drive has NO PROPELLERS. It relys instead on a thrust generation mechanism that mimics the propulsion of the fastest and most energy efficient fish in the ocean, members of the family Scombridae, (which includes the genus Thunnus), the giant bluefin tuna, which is known to achieve speeds of up to 36 knots over fantastically long distances, with minimal expenditure of energy. Working with faculty and students from an American college of engineering, Scioccodiaprile has truly crafted a “fish story” of great importance to the marine industry.
The remarkable performance achieved by the PTC propulsion system results from the hydrodynamic advantages of the shape and contours of the drive’s pod and the propulsion element, which combine to closely mimic a tuna’s swimming motions. The active part of the thrust system uses a vertically oriented articulated hydrofoil that bio-mimics the tail. The combination of the laminar water flow along the surfaces of this motori de mare and the wave-like, side-to-side motion of the “tail” deliver a continuous stream of rapidly moving water propelling the boat forward at speeds that range from barely perceptible to the maximum allowed by the available power and displacement.
Directional control for maneuvering is achieved by altering the pod’s azimuth angle, or in this case by pointing the “tuna” in the direction you want him to swim. The drive’s thrust can also be directed ±12° from the centerline of the drive pod through asymmetric actuation of just the “tail” itself. This is especially useful in precision maneuvering and during high speed turns by significantly reducing the need to alter the azimuth of the drive pod. Reverse maneuvering is achieved by turning the tuna through whatever angle is needed to accomplish the maneuver. In near-zero speed maneuvers, the pods in a twin installation may be set in opposition. The relative position of the pods is controlled by the system’s computer.
The energy needed to power the “tail” and to control the azimuth position of the drive pods comes from the vessel’s engine(s) via an hydraulic power system. The use of hydraulic propulsion in the marine environment is already well proven by its application in fishing fleets and in yachts of all sizes.
Eliminating the need for a direct mechanical connection between engine and drive system makes it possible to locate the engine(s) and their hydraulic pumps in the most beneficial position. The use of hydraulic power distribution makes it possible to power a PTC dual pod system from a single engine or from a combination of engine units of identical or differing horsepower. For example, modest speeds can be obtained through a small engine that simultaneously provides AC electricity, using a constant speed, pressure-flow compensated hydraulic motor-driven alternator.  Power for higher speeds can be provided from a second, more powerful engine, permitting efficient loading of the engines, minimizing fuel consumption and decreasing maintenance cycles.
Although the details of the motive system for the tuna “tail” are still under wraps pending patent applications, we were able, during a weekend visit with our good friend Ing. Paulo Sciocco, president of Scioccodiaprile, AG, to obtain a general understanding of the system. Paulo explained that the “tail” of the PTC is comprised of a series of vertical segments, called in Italian, “pezzo di coda,” joined to the aft end of the tuna shaped pod. Each segment contains a double-acting hydraulic cylinder to deflect that segment to one side or the other. A computer controls the distribution of pressure to cylinders in each of the tail segments creating the undulating motion that varies from a slow, gentle wave-like motion of the tail to the aggressive, powerful undulations needed to propel the boat in excess of 35 knots.
We were delighted to be invited for dinner and were joined by Paulo’s lovely wife, Aprile. Our dinner discussion over plates of calimari included the safety aspect of propulsion that operates without a propeller. As it turned out, Paulo’s daughter is an accomplished scuba diver and tested the PTC by swimming in close proximity to the pod and tail when the boat was moving at low speed, disbursing dye to visualize the flow. (Paolo referred to this maneuver as “chasing tail.”)
For details and schematics, visit the developer’s Web site at scioccodiaprile.com.