The most widely known systems of independent propulsion use a jet of fluid loaded with kinetic energy, or else a motor-driven propeller.

For water jet propulsion use is made of the impulse obtained by variation of the quantity of motion determined on a certain quantity of water.

The water is drawn in through a feed pipe, accelerated by a pump and discharged from a nozzle at the stern.

This system is advantageous for speeds greater than 70 knots but is complex and leads to structural and cost problems.

Propulsion by an underwater propeller creates problems of cavitation with interruption of the nappe that forms when a certain number of revolutions is exceeded.

Air jet propulsion, subject of an earlier patent by the same inventor, with a propeller inside the boat worked by an internal combustion engine, considerably improves efficiency and gives rise to an appreciable increase in thrust partly because it creates a cushion of air between the boat and the water.

The above patent application greatly improves the positive effects of air-jet propulsion as will now be explained.

Subject of the invention is a system of propulsion for boats obtained by using exoreactors, comprising one or more scroll conveyors and impellers worked by an endothermic motor, to accelerate the quantity of air drawn in and discharged through nozzles facing the stern inside a longitudinal, horizontal, semi-oval, rectilinear channel extending, aiong the keel, for its full length below the boat.

At the position of the channel extending for about one third of the boat, starting from the stern end there is a counter-channel that gives rise to an oval manifold inside which the nozzles operate.

The impellers of the exoreactors are fixed to a central shaft communicating, by means of a suitable transmission, with the shaft of an endothermic motor.

There are two exoreactors, placed side by side, that draw in air from intakes on the roof of the engine compartment of the boat, one on either side of the boat's transversal axis.

The exoreactors and the endothermic motor lie parallel across the boat in such a way that they occupy almost the whole volume of the hull corresponding to one third of its length starting from the stern.

A suitable power take-off on the endothermic motor operates a hydraulic pump connected to a hydraulic drive unit to which all the essential services of the boat are connected.

The ends of the scroll conveyors are slightly curved one towards the other to permit formation of nozzles parallel to the longitudinal axis of the channel thus producing a synergic effect between the jets from the two nozzles.

To make the boat move backwards, there is an arched screen, at the position of the nozzles and parallel to them, its concave side facing the bows, turning on articulations substantially at its geometrical axis, to permit its partial or total extraction from a hole under the hull thus compelling the jet of air, directed towards the

stern, to change direction downwards and towards the bows, this in order to slow down the boat or put it into reverse as required.

The nozzles are situated at the top of the manifold.

The endothermic motor discharges into the air while the petrol is catalysed.

The invention offers evident advantages.

Using a high-efficiency land-based engine of suitable ecological design, by means of the exoreactors a degree of thrust can be obtained such as will generate high-efficiency air-jet propulsion.

The ingenious placing of the exoreactors that, making very short strokes with consequent slight losses,. generate a flow of com- pressed air inside'the lower rear axial manifold, together with similar placing of said manifold, of an oval cross section, in relation to the lower side of the hull, permit propulsion of far greater efficiency than has hitherto been obtained in this field.

The jet of air is made much stronger not only by the synergy created between the two exoreactors, placed side by side, and by the position of their nozzles on top of the manifold below the hull close to the stern, but also, due to the effect of the channel running continuously below and in the centre of the hull, there is a kind of suction of water under the hull, mainly filling the channel and causing an exceptional reduction of the resistance that water is known to set up against any moving object.

Characteristics and purposes of the invention will be made still clearer by the following example of its execution illustrated by diagrammatically drawn figures.

Fig. 1 Side view of the boat, with exoreactor propulsion, cut through at a lower manifold.

Fig. 2 Plan view of the boat.

Fig. 3 Plan view of the boat cut through at the engine compartment.

Fig. 4 Longitudinal section of the boat at one exoreactor.

Fig. 5 Cross section of the boat at. the exoreactors.

Fig. 6 A rear view of the boat.

The boat 10 presents a hull 11 of a substantially semi-oval cross section, the bows 12 and the stern 13.

Under the boat and for its entire length stretches a longitudinal, reactilinear axial channel 30 of a semi-oval cross section, facing downwards and orientated substantially parallel to the plane of spontaneous immersion.

Starting from the stern and for substantially one third of the length of the boat, said channe ! 30 matches with a counter-channel 31 of substantially the same size and shape as the channel 30.

The structures of channel 30 and of counter-channel 31, both with thin walls, are such that their continuous matching for the whole length of said counter-channel 31 gives rise to an oval duct 32.

As may be clearly seen in Figure 6, the counter-channel 31 is joined to the hull 11 by fitting its longitudinal edges 34 into clefts 36 in the ribbing 35 on the hull at the two ends of the channel 30.

Propulsion is obtained by a pair of substantially discoid exoreactors 40 and 41 placed side by side, and comprising: -sharply curved tubular ducts 42 for suction of air; -scroll conveyors 50 with impellers 60 and blades 61; - a shaft 70 common to said impellers through the tubular ducts.

The tubular ducts 42 present air-entry grills 43 on the substantially horizontal roof 16 of the engine compartment 15, held stable by flanges 45.

At their exit said ducts present flanges 46 mounted centrally, in relation to the shaft of the impellers, on the outer walls of the scroll conveyors.

The internal walls 51 and 52 of the scroll conveyors are parallel and lie close together presenting, at the shaft 70 of the impellers 60, a structural connection for a central support 71 for said shaft, the thickness of which substantially fills the space between said walls and is based on the bottom of the hull by the supporting plate 75

The terminal nozzles 53 and 54 of said scroll conveyors 50 emerge from the opening 28 in the bottom of the hull, facing towards the stern 13, substantially alongside and parallel to the channel 30 and therefore to the walls of the duct 32.

The structure of the impellers 60 with blades 61 is subsantially that of a drum; they are fixed to the shaft 70 which, in addition to the central support 71, also has lateral supports 72 and 73.

To make possible the lesser distance of said supports 72 and 73, and to avoid vibrations from the impellers, in the ducts 42 are recesses 47 and a tubular housing 48 for the shaft 70, of a slightly greater diameter so that, at the recesses 47, vertical supports 72 and 73 can be placed for the shaft 70, these being joined to the base of the hull 11 by supporting plates 76 and 77.

At one end of the shaft 70, immediately beyond the support 72, a pulley 91 is fitted; this, by means of its continuous belt, permits a kinematic connection, by means of a second pulley 92, with the shaft 81 of the endothermic motor 80 above which is a head 85.

At the rear end of said motor is a socket 100 for a hydraulic pump 104 to be used for the fluid controls of the various services, said pump being connected by the manifold 102 to the hydraulic drive unit 101 placed substantially at one wall of the hull 11.

A device for stopping and reversing the boat is placed between the pair of exoreactors 40 and 41 and the endothermic motor 80, this comprises a sort of semicylindrical screen 120 whose geometrical axis, substantially orthogonal to the axes of the nozzles, is articulated 128 by arms 121 to a support 122 on the bottom of the hull At the top said screen 120 is connected by an articulation 127 to a bridge 125 and, by a second articulation 126 to the piston 124 of a hydraulic cylinder 123 fixed to the bottom of the hull.

In its idle position said arched screen 120 remains inside a housing 28 in the hull and has no effect on the jets emerging from the nozzles of the scroll conveyors.

If it is desired to put the boat into reverse it is sufficient to use the relative command that brings said arched screen onto the manifold 32, thus causing reversal of the jets 135.

Placed respectively on the two sides of the engine compartment are the water tank 109, the petrol tank 106 and the batteries 107.

It will be clear that the impellers on the exoreactors, worked by the endothermic motor, accelerate the quantity of air drawn in by the impellers, this being then discharged, with increased motion, through the nozzles placed inside the manifold under the hull.

Using suitable systems of regulation 22,24,25, as envisaged in a previous patent by the same inventor, hydraulic controls can determine the power levels and direction of movement, orientate the boat as desired and reverse the direction of the jets of air inside the manifold, causing the boat to move forward, backward, to the right and to the left, as required.

Further devices, not shown for the sake of simplicity, enable the boat to be moved within a restricted space, such as in a port, and to turn it round itself in both directions.