Scope of the invention

This invention relates to a propulsion system for boat where the thrust is provided by the rotation of two rotors arranged in such a way as to be fully submerged and to remain underneath the hull lines. State of the art

Quite a few types of propulsion devices are known in the nautical field, as they are designed to cause boats to move forward, such as oars, paddles, rotors driven by the upper and lower limbs, motors with submerged propellers, motors that cause the rotation of paddles, water-jet propellers, air-screw propellers as those of hovercrafts, and sails that are known to take advantage of the power of the wind. In the field of small pleasure boats, the most common means of propulsion are oars, leg- operated rotors that are vertically semi-submerged, both internal combustion and electric outboard motors and sails. All the listed means have thrusting and/or steering elements, such as oars, propellers, rotor paddles and rudders that are external to the hull lines, so that they are often a problem when getting by shallow water and a potential risk, particularly to bathers. For instance, propellers are known to be dangerous, as they may hurt bathers, entangle fishing nets or the mooring lines of other boats in ports and, at the same time, they limit the possibility of getting by shallow water or reaching shore. Besides, there is the well- known possibility of hurting bathers with one's oars and the difficulty when using a row boat in coming alongside a quay or another boat, all the more so when the latter is also a row boat, in addition to the well-known inconvenience of having to row facing the stern. The subject matter of this invention is a boat propulsion and steering system with fully submerged rotors that solves all the problems referred to above, allowing both the forward movement of the boat and its steering. The system proves particularly suitable . for being installed on small boats. Description of the invention According to this invention, the system consists of a pair of propellers, which are symmetrical with respect to the boat center line, fully submerged, inside the hull lines lying within the bottom surface of the hull, or inside the surfaces if it is V-shaped, close to the transom.

Each propeller is made up of a horizontal impeller fulcrated on the boat by means of a vertical axis. The impeller rotates in a cylindrical casing the upper flat surface of which is closed; the cylindrical lateral surface is open towards the outer lower area of the transom; the lower surface corresponding to the bottom surface of the hull is open at the center and in the sector where the blading operates in agreement with the direction of movement and, therefore, in the outer lateral area, while it is closed in the sector where the blading rotates in the direction opposite to the direction of movement and, therefore, in the lateral area towards the boat center line. Each impeller is rotated by suitable means that may be both hand-operated and engine-driven.

Description of the drawings

The invention shall now be described in an explicatory but not limiting example of realization with reference to the attached drawings where: Figure 1 shows an upper three-quarter axonometric view of the propulsion system installed within a boat that may be operated by means of levers

Figure 2 shows a partially sectioned lateral view of the propulsion system installed within a boat that may be operated by means of levers

Figure 3 shows a partially sectioned schematic view of the stern of a boat and of the propulsion system viewed from below

Figure 4 shows a partially sectioned schematic view of the stern of a boat and of the propulsion system

Figure 5 shows an axonometric view from below of the stern of a boat with the propulsion system installed .. Figure 6 shows a three-quarter view from above of the propulsion system installed on a boat that may be operated by means of two levers

Figure 7 shows an axonometric back view of the propulsion system operated by means of two levers

Figure 8 shows ah axonometric front view of the propulsion system operated by means of two levers

Figure 9 shows a three-quarter axonometric back view of a single rotor and the operating lever Figure 10 shows a three-quarter axonometric front view of a single rotor and the operating lever

Figure 11 shows a schematic view of one of the rotor operating levers in its possible positions Figure 12 shows a schematic view of a type of wheelwork to which the impellers are connected

Figure 13 shows a schematic view of an application of the force resulting from oscillating pedals to the movement of the impellers

Figure 14 shows a schematic view of a variant of the application referred to in figure 13 Figure 15 shows a partially sectioned schematic view of the stern of a boat and of the propulsion system in a variant of the one shown in figure 3.

Description of realization examples

With reference to the said figures, when hand operated, the boat propulsion and steering system with fully submerged rotors referred to in this invention result to be made up by: . - a pair of propellers generally shown as (1), each one of which comprises a horizontal impeller with reverse blading (2);

- a vertical rotation axis (3) having a sufficient length to connect the horizontal, impeller (2) with means suitable for transmitting the force required for the rotation;

- gears (4, 5) with a free-wheel connection to the vertical rotation axis (3) suitable for transmitting the rotation force to the axis (3) and, consequently, to the horizontal impeller (2) in the proper direction;

- a housing for each impeller (2) obtained in the outer hull of the boat, delimited by a totally closed upper flat surface (6); a cylindrical lateral surface (7) open (7a) towards the outer lower area of the transom; a flat lower surface corresponding to the bottom plane of the hull open at the center and in the sector where the blading operates in agreement with the direction of movement of the boat (outer lateral zone) and closed in the sector (8) where the blading rotates in the direction opposite to the direction of movement (lateral zone towards the boat center line);

- motion generation devices for each impeller that, in the hand-operated solution, comprise an angled lever (9) fulcrated at the bottom in (11) on the inner part of the boat side; a rod (10) hinged to the lever (9); an element (12) hinged to the rod (10) and fulcrated on an axis (16), that is shaped, on two levels, with toothed circular sectors described by different radiuses: the upper toothed circular sector (13) has inner toothing and is enclosed by radiuses of greater length than the lower toothed sector (14) that has outer toothing; each toothed circular sector meshes with a crown gear (4 and 5) with free-wheel clutch on the rotation axis (3) integral with the impeller (2) that always rotates in the same direction whether the lever (9) is moved in the direction that goes from stern to head or the other way around; the different ratio between circular sector (13, 14) and constant crown gear (4, 5) compensates for the different force exerted on the lever in the thrust (lower) and in the traction (higher) of the levers (9) by the rowing person. The levers (9) that, as previously pointed out, allow the operation of the impellers (2), may be subjected to a 180° rotation at their knee (9a) so that they may be in an advanced position towards the head or towards the stern, in relation to the preference of the person operating them and the position the latter needs to take when rowing owing to the loads on board. As previously pointed out, the impellers (2) may also be driven by electric or internal, combustion engines with simple controls that permit to change their rotation speed; in so doing, both the speed of the boat and its direction are affected. As it may be noted from the foregoing description, the housings where the impellers (2) rotate are partly closed (6, 8). In these areas, the bladings tangentially accelerate the water flow and then discharge it in the open sections (7a); the central areas of the impellers (2), free and relatively under reduced pressure, accommodate and draw in the water that slides under the hull.

As specified, the impellers (2) allow steering the boat causing it to move ahead or to veer to the right or to the left by simply changing the speed of one or the other impeller (2) with excellent handling qualities due also to the fact that in the areas where the impeller bladings are close to leaving the free sectors (7a) in order to enter the closed ones (6, 8), the reaction thrusts on the blades are angled backwards, towards the center line of the hull. As a result, there is a moderate loss of efficiency in the direction of movement, but a considerable increase in the steering and veering moment, so much so as to allow the boat driven by a single propeller to rotate round itself when stationary and to leave the 90° angle of the walls of a dock when the boat head has been driven there. Contrary to what happens -with wheels with vertical blades, the total submersion of the impellers (2) causes their functionality to be unaffected by draught or wave motion problems.

A further advantage is represented by the fact that, as previously pointed out, the axes (3) of the impellers (2) are positioned vertically and extend well over the maximum water-line and, therefore, require no sealing device, with advantages that are by no means secondary.

In the realization example described above, the impellers are allowed to rotate by means of hand-operated or motor-driven motion generators that are independent for the two submerged impellers. A few application solutions where the impellers are driven by a single motion generator and are connected with different solutions to the motion generator and among themselves are described, and illustrated below. In a solution shown in figure 12, the rotors with the axes of the two submerged impellers, 25 and 26, are rigidly connected to the pinions 17 and 18 that, in their turn, mesh with the wheels 19 and 20; hence, the impellers rotate in the opposite direction at the same speed; the motion may be exerted by any motor connected in a preferred point of the kinematic chain 17, 19, 2O ₅ 18; furthermore, a control for the temporary release of pinion 17 from axis 25 and pinion 18 from axis 26 is provided with a view to making the most of the thrust of one of the impellers for steering the boat. Figure 13 shows the solution where the impellers are caused to rotate by muscular force preferably of the legs, for example, by means of oscillating pedals, with to-and-fro movements, where the wheels 19 and 20 alternately receive the motion through two free-wheel couplings with the projecting wheels 21 and 22 driven by the toothed belt 24 that moves With the to-and-fro movement exerted by the pedals. In figure 14, the wheels 21 and 22, always with an alternate free-wheel coupling with the wheels 19, 20, are toothed and mesh with wheel 23 that has a dual rotation direction in order to obtain the continuous rotations of the axes 25 and 26 from the alternate motion of traction of the belt-24 working on the projecting wheel 27, rigidly connected to the gear wheel 23. In this version, a change-speed gear may be obtained by replacing wheel 27 with a series of wheels of different diameter, as it happens for instance with the pinions of the back hub of a bicycle. A further means of operation of wheel 27 may be obtained having recourse to two racks tangent to the transverse diameter of wheel 27, which is a toothed wheel. Even in this case, wheel 27 may be made by a series of wheels having different diameter on the outer edges of which the racks work to obtain the speed change.

In the event that it is not deemed necessary to privilege the steering effect, the impellers

— rather than having areas for the outflow towards the two external sides of the transom, as shown in figure 3 — shall have a single area of central thrust with' the bladings and the reverse direction of rotation, and the bottom opening of the impeller casings shall be modified, as clearly shown in figure 15.

For veering purposes, flow diverters may be used even within the impellers outflow areas with no obstruction outside the hull lines.