EP2222549A1

EP2222549A1 - Translating chariot for fin propulsion

Info

Publication number: EP2222549A1
Application number: EP08858400A
Authority: EP
Inventors: Jacob Govert Vermeiden
Original assignee: AP Moller Maersk AS
Current assignee: AP Moller Maersk AS
Priority date: 2007-12-10
Filing date: 2008-12-09
Publication date: 2010-09-01
Also published as: JP2011506172A; CN101909983A; KR20100098686A; US20100285703A1; WO2009074578A1

Abstract

Maritime propulsive mechanism employing oscillating fins (4). The mechanism comprises a chariot (3) transferring propulsive power from a source of propulsive power (10) to the fins (4). Oscillating means, driven by a source of propulsive power (10) having a first axis of rotation (17), for oscillating the chariot (3) are provided. The fins (4) are rotatable about a second axis of rotation (6) wherein the first axis of rotation (12) forms an angle α with the second axis of rotation (6). The fins are connected to the chariot (3) via two connection points (5), (16). The oscillating means can be interposed between two chariots (3), and the oscillating means imparts flywheel-effect on the system. Forces exerted on the chariot transported through the chariot (3), and borne by bearings (9).

Description

Translating chariot for fin propulsion

Field of invention

The present invention relates to a propulsion system for a maritime vessel wherein the employed means for propulsion includes flapping and transversely translating foils or fins.

According to one aspect, the present invention relates to a propulsive mechanism for a maritime vessel propelled by water engaging fins or foils.

The fins or foils are driven such that the fins or foils translate in directions substantially transverse to a longitudinal axis of the maritime vessel.

The mechanism inter alia comprises:

- at least one source of propulsive power having an output shaft forming a first axis of rotation,

- at least one chariot, provided within the hull of the maritime vessel and transferring the propulsive power from the source of propulsive power to the fins or foils,

- means for providing translation of the chariot inter alia comprising a crank, and

- an arrangement connecting the fins or foils to the chariot and allowing said fins or foils to rotate about a second axis of rotation in a controlled manner.

The chariot is preferably provided inside the hull of the vessel and is via oscillating or translating means connected to at least one source of energy developing at least part of the propulsive power. It must be understood that the hull of the vessel or ship accommodates the propulsive system, apart from the water engaging foils or fins, incl. all necessary technical means.

Background

It is recognised that fish and sea mammals, which move and manoeuvre in water inter alia by means of oscillating fins, moves with higher propulsive efficiency than today's maritime vessels.

No technological equivalent to fin propulsion has so far been implemented in maritime vessels.

The present invention is an important practical element to easily realize efficient and operative flapping propulsion based on the combination of one periodical translating movement and possibly one periodical rotation movement of one or several fins under the ship.

The oscillating motion of a fishtail can be simulated and generated either by rotation of a fin, or, as is the case with sea-mammals and tuna-related fish, by a combination of at least one periodical translation and one periodical rotation of the caudal fin.

Today, almost every waterborne vessel, regardless of size, service speed and application, are propelled by one or more rotating propulsive elements.

The propulsive elements, e.g. propellers, jets, ducted propellers or pump jets etc., are rotating about their own axis. On larger vessel, the propellers are rotating at about 50-500 rpm.

The propellers are carefully designed for their particular application. One important objective for the designers are to limit the vessels overall fuel consumption. This is achieved through careful design of several parameters such as hull form, propulsion plant and propulsive elements.

The efficiency of today's most effective propellers rarely exceeds 80 %, in fact efficiencies of 30-70 % are generally accepted, leading to unnecessarily large power plants and increased fuel consumption.

Therefore, considering the above mentioned inexpediencies, usefulness of a fully operational and improved low-tech but high-efficiency marine propulsion system is apparent.

Background art

Propulsion by means of oscillating fins possesses attractive features such as higher efficiency than rotating propellers and inherent steering, which eliminates the need for a separate rudder with the associated costs and the associated reliability issues; in addition it frees volume inside the hull for increased cargo accommodation. The higher efficiency is achieved through lower impulse losses, lower hydrodynamic friction losses, lower induced drag losses and a lower drag on the hull itself, and results in either lower fuel consumption and lower installed power for the prime movers, or a higher service speed with the same installed propulsion power and fuel consumption.

Important challenges for oscillating fins consist in avoiding large mechanical friction losses, and consist in providing reliability and safety comparable to the rotating propellers. US patent no 5,401 ,196, published March 28, 1995 (TRIANTAFYLLOU et al.) disclose a propulsion system employing flapping foils. The patent, which teaches a system utilizing at least one foil, discloses a propulsive system wherein a foil is oscillated in a direction transverse to the vessel's sailing direction and is rotationally oscillated about a vertical axis. Preferably, according to the US patent, the propulsive system is built up from a plurality of foils which are oscillated out of phase resulting in the propulsive elements thrust in a direction transverse to the sailing direction is insignificant.

Where an even number of foils are used, half the foils are preferably oscillated 180° out of phase with the other half of the foils. Where e.g. three foils are used, the foils are oscillated 120° out of phase with each other.

The main features of a mechanical embodiment of the propulsion system as disclosed in the US patent will be explained below.

Figures 4A, 4B, 5A, 5B & 5C illustrate an embodiment for a foil propulsion system in accordance with the US patent. The propulsive system is build up from two foils (10), each connected via a shaft (34), through a slit (36) in the aft section of the hull (30) to a table (40). The extent of the slits (36), as can be seen in figure 4A and as illustrated by the arrows (38), being greater than the total maximum heave amplitude for the foils. As may best be seen in figure 4B, each table (40) has two or more wheels or rollers (42) mounted to the forward underside and to the rear underside, in which the wheels or rollers ride in corresponding tracks (44) mounted to hull (32). The tables (40) and the foils (10) attached thereto are thus free to move both directions along one axis (38), and are fixed from movement in any other direction.

Conclusively, the mechanism according to the US patent is working through a number of slits (36) established in the hull (32), each transverse to the vessels forward sailing direction, and the extension of the slits (36) exceeding the transverse motion of the foils. The fins are also rotating under power around axes placed such that rotation substantially affects the angle of the foil with the direction of motion of the ship. All disclosed axes of rotation are established as substantially vertical axes. Further, the fins are driven by separate motors; and the motors also rotate about substantially vertical axes.

The teaching according to the patent has so far only seen limited practical application in propulsion of maritime vessels.

US patent no 6,877,692 B2, published April 12, 2005 (LIU) disclose a propulsion system for a submarine. The patent teaches propulsion based on "thuni-form" movement of foil members. The foil members are mounted to the hull for reciprocating oscillating movement towards and away from each other creating the forward movement due to compression of water between the foil members. The patent does not suggest employment of fin propulsion for surface vessels.

WO 99/06272 A1 (R. R. SAIL INC) teaches a propulsion system for a water craft having means for propulsion extending below the water line. The propulsion means comprises a pair of flappers each adapted to oscillate through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of the watercraft. Means are operatively associated with the propulsion means for applying input force to the propulsion means. The flappers twist to form an angle of attack for providing forward thrust with respect to the longitudinal dimension of the watercraft while moving in both directions along the arcuate path.

US 6877692 B2 (LIU PENGFEI et. al) teaches a propulsion system based on a "thuniform" movement of a foil member to achieve desired directional movement of a vessel such as an unmanned submarine. A pair of foil members is mounted to the hull for reciprocating oscillating movement towards and away from each other, creating forward movement due to the compression of a fluid medium between the foil members and the expulsion of the compressed fluid rearward of the foil members. Each foil member is mounted to a pivot shaft for limited rotational movement with respect to the vehicle body. Damping means are connected between each pivot shaft and its associated foil member so that during operation of the propulsion system damping torque will offset hydrodynamic loads imposed on the foil members by the fluid medium. The damping means will in turn control the pitch angle of the foil members during operation, meaning that a thrust is generated for rigid foil members when moving at zero forward speed.

WO 03/026954 A1 , published April 3, 2003 (Inocean) suggests a system utilizing a sinusoidal pattern of movement for propulsion or energy recovery. The system comprises a plurality of rigid hull elements arranged in a row and rotatable attached to one another for rotation about parallel axes of rotation across the longitudinal dimension of the row of hull elements. The system further comprises movement devices for rotating the hull elements relative to one another or movement devices for recovery of energy as a result of rotating the hull elements relative to one another.

WO 2006/038808 A1 , published April 13, 2006 (Clavis Biopropulsion) suggests a device comprising at least one transversely translating fin. The device encompasses actuating and drive means allowing substantially free oscillating motion of the fin. The device operates by means of an impulse, established by drive means, every so many cycles and spring are used to store the pulsating energy provided by the drive means.

Today's known fin propulsion systems encompass a number of fundamental inadequacies, some of which are: - failure to teach a solution wherein the substantial forces, in the transversal plane, originating from the efforts of the oscillating or translating means incl. reaction efforts stemming from the fins, acceleration and deceleration forces stemming from the oscillating or translating parts and the reaction forces of the hull induced on the system are both minimised and absorbed safely and reliably by the hull with minimum friction losses; and

- failure to teach a solution wherein the substantial forces, in the longitudinal plane, that originate from the propulsive forces inc. the reaction forces on the hull are transferred to the hull in a safe and reliable way with limited friction losses.

Further, the prior art fails to suggest a transversely translating fin propulsion system wherein the source of propulsive power is a conventional engine for a maritime vessel, and where the engine is, either directly or indirectly, mechanically coupled to the propulsive system.

The required translation speed of the oscillating propulsive members are high, sometimes reaching 10 m/s. Depending on the particular application, the G-forces applied on the system could easily reach 5 G substantiating the need for an extremely rigid supporting structure for the operation of the oscillating propulsion system.

Brief description of the invention

It is an objective of the present invention is to set forth a propulsive mechanism utilizing the known transversely translating and flapping foils or fins as disclosed above, however, according to the invention, this being an operable mechanism that introduces distinct contributions and advantages over prior art. Some of the advantages are: - providing a simple and reliable system which allows a typical two- stroke or four-stroke marine engine, arranged with its crankshaft oriented substantially parallel to the baseline of the vessel, to be applied in connection with fin propulsion where the fins are driven in transverse translation with respect to a longitudinal axis of the vessel.

- providing a system being able to cope with substantial forces stemming from one or more of the following:

a) the means for propulsion interaction with the water, b) the forces stemming from the system it selves, and c) the forces stemming from deflections of the hull

Constructing a propulsive system according to the introductory part of this specification will lead to the abovementioned clear benefits, in particular upon the first axis of rotation of the output shaft of the source of propulsive power forms an angle (α) with the second axis rotation of the fins or foils.

Further, according to one embodiment, the first axis of rotation of the source of propulsive power is substantially parallel to said longitudinal axis of said vessel, and the second axis rotation of the fins or foils is oriented such that the angle (α) is 90° +/- 45° or less, e.g. 90° +/- 30° or even 90°+/- 20°.

According to one embodiment, the fins or foils is connected to the chariot via at least two connection points, allowing the fins or foils to rotate about the second axis.

According to one embodiment, the propulsive mechanism comprises at least two chariots, one being arranged in front of the other, wherein between means for providing translation of one or more chariots at least partially is interposed.

According to one embodiment, the least a part of the means for providing translation of the chariot imparts flywheel-effect to the propulsive mechanism.

According to one embodiment, the forces exerted on at least one chariot by hull, fins or foils and means for providing translation of the chariot and the resulting moments of the forces, are at least partially transported or conveyed through the chariot, and borne by at least two bearings.

According to one embodiment, the chariot accommodates means for applying rotational movement to the fins or foils.

According to one embodiment the means for rotating the fins or foils is controlled such that an optimum or desired angle of attack between the fins or foils and the water through which the vessel is propelled is obtained.

According to one embodiment, the one or more chariots are powered from one, preferably single, source of propulsive power.

According to one embodiment, a chariot is provided without accommodating fins or foils.

According to another aspect of the present invention, a method of propelling a maritime vessel by means of a propulsive mechanism according to the teachings of the specification is provided.

Brief description of the drawings Figure 1 shows a principal and sectional side view of a maritime vessel prepared for propulsion by means of flapping fins or foils.

Figure 2 shows a principal top view of the maritime vessel according to figure 1.

Figure 3 shows a principal transverse and sectional view of a maritime vessel incorporating a propulsion mechanism according to the present invention.

Figure 4 shows a principal and sectional side view of a propulsion plant of a maritime vessel incorporating a propulsion mechanism according to the present invention.

The elements disclosed in the above figures are mutually and conveniently scaled, and serves the purpose of illustration only.

Detailed description of the invention with reference to the figures

Figure 1 shows a sectional side view of a maritime vessel 1 comprising an engine room or propulsion plant 20 provided in its hull 2. Means for propulsion in the form of fins or foils 2 can be seen extending from a region below the propulsion plant 20. At least a portion of the means for propulsion will under normal operating conditions be submerged below the water line 30.

Figure 2 shows a sectional top view of a maritime vessel according to figure 1.

Figure 3 is a sectional and transverse view through the engine room or propulsion plant 20 of a maritime vessel 1. An oscillating or translating chariot 3 is provided in the hull 2, and connected to propulsive means in the form of fins or foils 4. Figure 4 is a principal and sectional side view illustrating the propulsion mechanism according to the present invention.

The chariot 3 is on one portion, and via means being able to oscillate or transversely translate the chariot 3, connected a source propulsive power 10 having an output shaft defining a first axis of rotation 17.

The chariot 3 is on a second portion, as already mentioned above, connected to fins or foils 4.

The fins or foils 4 are connected to the chariot 3 via at least two connection points 5, 16. The connection points 5, 16 may constitute bearings allowing the fins or foils 4 to rotate about a second axis of rotation 6.

The first axis of rotation 17 forms an angle α (shown in figure 4) with the second axis rotation 6.

Depending on the embodiment, the angle could be an obtuse angle, an acute angle or a straight angle. The angle α will be determined substantially by the inclination of the fins or foils 4 in respect to a substantially horizontal line 17 defined by the crankshaft of the engine 10 developing the propulsive power.

Forming an angle between the axis 17 of the delivered rotational propulsive power and the fins or foils 4 resolves a strong desire in realizing propulsion by means of fins or foils powered from a conventional and economical proven, reliable and available source of energy.

The propulsive power may stem from one or more engines, e.g. slow speed or medium speed engines. Further, it will be possible to realize the invention utilizing any kind of turbines powered by gas, steam or even nuclear energy. The propulsive means 4 may, as already suggested above, constitute fins or foils suitable for propulsion by means of fin propulsion utilizing oscillating or transversely translating fins or foils.

The properties of the propulsive means 4 may be selected such that optimal development of thrust is achieved when operated as per the introductory part of this specification.

The chariot 3 may accommodate means 7 for pivoting or rotating the propulsive means 4. The means 7 may be in the form of several different arrangements, e.g. electric or hydraulic motors, ram's, mechanical links incl. springs etc.

The chariot 3 may form part of the means 8 being able to oscillate or transversely translate the chariot 3, e.g. form one part of a crank arrangement connected to a rotatable transmission element.

The figures 3 and 4 illustrate the means for oscillation or transverse translation inter alia comprising a driving wheel 8 located above a driven wheel 11. The means for oscillation or transverse translation will prove equally beneficial in embodiments wherein the driving wheel 8 is located below, inside or even at the sides of the driven wheel 11.

The driving and driven wheels 8, 11 may constitute toothed wheels, interconnected or not, friction drives, belt/chain drives or any other suitable drive mechanism.

Further, it will be possible to interpose an offsetting gear (not shown) between the means for oscillation or transverse translation of the chariot 3 and the source of propulsive power 10, rendering it possible arrange the source of propulsive power at desired locations.

The chariot 3 may form part of a sealing structure where the sealing structure operates as means for sealing and partition, i.e. separating the interior of the hull 2 from the environment outside the hull 2.

The chariot 3 may be manufactured, either as an integrated part or component or as interconnected parts, in mild steel, high tensile steel, stainless steel or any other suitable material such as fibre reinforced plastic or fibre reinforced metal. Further, the chariot 3 may be manufactured in any suitable profile, e.g. a welded structure of tubular elements, open web or even a honeycomb structure manufactured in a non-steel material.

According to one embodiment, two propulsive systems, port- and starboard sides respectively, are provided in the hull of a maritime vessel.

The systems may be driven by one source of propulsive power 10 which may constitute a slow speed two stroke main engine directly or indirectly coupled to a transmission which may form part of the transverse translating or oscillating means.

The systems may, as shown on figure 2, be arranged offset in the vessels 1 longitudinal direction. Offsetting the systems may provide space for the heave motion of the chariots 5 incl. provision of space for transverse translating or oscillating sealing means.

The oscillating means, which may further comprise two cranks each acting on one chariot 5, are interposed between the chariots 3 as can be seen in figure 4. Further, the oscillating means may impart a flywheel-effect on the mechanism. Additional flywheels, independent or not, may further be provided to the system.

Any flywheels may at convenience by driven through one or more gearings, and the flywheels may be coupled to the system via one or more couplings or clutches.

Upon the systems being operative, the source of propulsive power rotates the first toothed wheel 8 which is engaged with the second toothed wheel 11.

Together, the two wheels 8, 11 , may form a gearing which suitable may be determined from various parameters e.g. the characteristics of the selected main engine and the selected characteristics of the propulsive elements etc.

The second toothed wheel 11 may, on the aft and forward sides and under 180° angular displacement, be provided with journals 12 which may be connected to sliding devices 13.

The sliding devices 13 being slid ably interconnected with sliding bars 14 rigidly connected to the chariots 3.

Upon rotation of the second toothed wheel 11 , the sliding devices 13 are manoeuvred lengthwise along the sliding bars 14 while the transversal resultant causes the chariots 3 to oscillate or translate whereby propulsive power is transferred to the environment via the propulsive means 4.

The above preferred embodiment may in no way be considered as limiting for the scope of the invention as such. Forces exerted on the chariot 3 by the hull 2, the propulsive means 4 and the oscillating or transversely translating means, incl. the resulting moments thereof, are at least partially transferred through the chariot 3, and borne by at least two bearings 9. The bearings 9 may at convenience encompass at least two degrees of bounded liberty.

A component of the forces exerted on the chariot 3 by the hull 2 and propulsive elements 4, may in the longitudinal plane be transmitted through the chariot 3 in a manner that any structure of the chariot 3 is subjected to associated moments lower than 1/5th of a reference moment. The forces in the longitudinal plane are borne by at least two bearings with at least two bounded degrees of liberty compared to the hull.

The propulsive systems as per the present invention may be arranged or provided in the hull 2 of a maritime vessel under several configurations, some of which are:

A. as port and starboard systems being offset in a longitudinal direction, as illustrated by figure 2, B. two systems being juxtaposed or being placed longitudinally one in front of the other, either totally or partially, and C. one single system arranged substantially in the vessels longitudinal centreline 8.

The propulsion mechanism according to the present invention is not in any way limited to one configuration above another configuration.

As forces acting on the hull, e.g. stemming from accelerations of the components of the propulsion system (i.e. vibrations), together with transverse components of the propulsive power delivered to the environment (i.e. hydro forces) may be preferred neutralized or equalized, embodiments encompassing two or more systems may under certain embodiments be preferred over a system encompassing only one propulsive system. (Item C above).

Under embodiments according to item C. above, the forces acting on the hull may by counteracted/equalized or balanced by means of certain dedicated arrangements.

The balancing issues comprise two aspects which may be divided into two components:

- balancing / cancelling sideways efforts stemming from accelerations of mass (i.e. the components of the propulsion system), and

- balancing / cancelling sideways efforts stemming from hydro forces

Further, the balancing issue may also encompass an energetic aspect, as the energy cycle needed for the chariot 5 has a constant component and an oscillating component of large amplitude, which may be provided in a controlled manner.

The vibratory issues may be solved by the provision of a second translating element or chariot (with or without fins) which through careful selection of mass, phase shift, amplitude, and possibly hydro-forces largely cancels out the adverse sideways forces.

The issues relating to the energetic aspects may be solved by means of below two proposals which are able to counteract the sideways forces generated by the fins or foils 4 interaction with the water: - providing two translating elements with mass that equalize each others vibrations, thereby constituting a system with a harmonic energy characteristic, and choosing its phase shift such that its energy cycle is in phase opposition with the energy cycle of the system (chariot and impulse counterweight), thereby constituting a larger system with need for limited variation in energy supply throughout a cycle, and that can therefore be driven by conventional power sources such as diesel engines, electric drives etc., or

- providing at least one flywheel to the system which may be connected to a crankshaft which is in turn connected to the chariot 3 through a slider, which either stores or supplies energy to the system (chariot + impulse counterweight + power source) as required, and thereby ensuring substantially constant rotational speed of the crankshaft which entails harmonic translation of the chariot

The vibrations, which preferable also is equalized as the impulses may be substantial, may be equalized by means of mass rather than by means counter moving fins.

The issues relating to the vibration aspects may be solved by a second translating element, or chariot, counteracting the forces generated by the acceleration/deceleration of the chariot/translating element, where translating element or chariot has a mass and demonstrating oscillating transversal forces, due to mass acceleration and a carefully chosen phase-shift with the chariot 3, which at least partially counteract the transverse forces originating from said chariot 5 incl. accommodated propulsive means 4.

Further, the vibratory issues as well as the balancing issues may be counteracted by means of arrangements with varying mechanical properties such varying mass and varying radiuses. As per the above, rotation or pivoting of the propulsive elements 4 may be realized by means 7. The means 7 may control the flapping foils or fins such that the fins on average pitch less than the apparent flow angle caused by the water flow around the hull and the translation speed of translating element or chariot 5, for effective propulsion, such that the lift caused by flow over the fins is directed forward on average in the case of forward propulsion.

Definitions

Transversal plane: plane defined by the rotation axis of the fin and the average oscillation direction of the chariot. The plane may be tilted forward or backward, and may be facing slightly to port or starboard.

Longitudinal plane: plane defined by the vertical direction and the direction normal to the transversal plane

Reference moment: value resulting from multiplying the maximum force exerted by oscillating means by the span of the fins

It should be emphasized that the term "comprises/comprising/comprised of when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

1. A propulsive mechanism for a maritime vessel propelled by water engaging fins or foils (4) driven such that said fins or foils (4) translate in directions substantially transverse to a longitudinal axis of said maritime vessel, said mechanism inter alia comprises:

- at least one source of propulsive power (10) having an output shaft forming a first axis of rotation (17),

- at least one chariot (3), provided within a hull (2) of said maritime vessel, and transferring said propulsive power from said source of propulsive power (10) to said fins or foils (4),

- means (8) for providing translation of said chariot (5) inter alia comprising a crank,

- an arrangement connecting said fins or foils (4) to said chariot (3) and allowing said fins or foils (4) to rotate about a second axis of rotation (6) in a controlled manner, characterized in that said first axis of rotation (17) forms an angle (α) with said second axis rotation (6) of said fins or foils (4).

2. The propulsive mechanism according to claim 1 , wherein said first axis of rotation (17) of said source of propulsive power (10) is substantially parallel to said longitudinal axis of said vessel, and wherein said second axis rotation (6) of said fins or foils (4) is oriented such that said angle (α) is 90° +/- 45°.

3. The propulsive mechanism according to claim 1 or 2, wherein said fins or foils (4) are connected to said chariot (3) via at least two connection points (5), (16), allowing said fins or foils (4) to rotate about said second axis (6).

4. The propulsive mechanism according to claim 1 wherein the mechanism comprise at least two chariots (3), one being arranged in front of the other.

5. The propulsive mechanism according to claim 4 wherein said means (8) for providing translation of said chariot (5) is at least partially interposed between two chariots (3).

6. The propulsive mechanism according to any of the preceding claims, wherein at least part of said means (8) for providing translation of said chariot (3) imparts flywheel-effect to said propulsive mechanism.

7. The propulsive mechanism according to any of the preceding claims, wherein forces exerted on said at least one chariot (3) by said hull (2), said fins or foils (4) and said means for providing translation (8) of said chariot (5) and the resulting moments of said forces, are at least partially transported or conveyed through said chariot (3), and borne by at least two bearings (9).

8. The propulsive mechanism according to any of the preceding claims, wherein said chariot (3) accommodates means (7) for applying rotational movement of said fins or foils (4).

9. The propulsive mechanism according to claim 8, wherein said means (7) for rotating said fins or foils (4) is controlled such that an optimum or desired angle of attack between said fins or foils (4) and the water through which said vessel is propelled is obtained.

10. The propulsive mechanism according to any of the preceding claims, wherein said one or more chariots (3) are powered from one source of propulsive power (10).

11. The propulsive mechanism according to any of the preceding claims, wherein at least one chariot is provided without accommodating fins or foils (4).

12. A method of propelling a maritime vessel by means of a propulsive mechanism according to any one of the preceding claims.