Patent Description:
Today, a relatively large proportion of the international transport system relies on large-scale freight ships, transporting large volumes of goods such as oil, foodstuffs and packaged products. For such transport, a major cost is fuel. Reducing fuel consumption is therefore of great concern for economic reasons, in addition to it being imperative for reducing the emission of carbon dioxide and other environmentally damaging compounds.

Another problem is the ecological damage imparted by the large propellers needed for such large vessels.

It has previously been described, such as in <CIT>, how a dolphin fluke-shaped fin can be used to propel a floating vessel more efficiently and with less impact on the environment through which the vessel is propelled. Such a fin, which may be of different sizes and which may be the more or less the shape of a dolphin fluke, is hence herein denoted a "fluke".

However, to the knowledge of the present inventors there has not been presented an efficient way to provide fluke drive to a large vessel, such as a large-scale freight ship.

Such a solution should provide an efficient way to propel a large vessel, and also be possible to retrofit onto an existing vessel in a cost-efficient manner, maintaining full vessel security, stability and integrity.

An additional problem is to achieve a fluke design providing a highly efficient energy transfer at a relatively low reciprocal movement frequency, adapted for propelling a relatively large vessel using a relatively large fluke.

<CIT> discloses the use of a fluke drive on a ship.

The present invention solves the above described problems.

Hence, the invention relates to a fluke drive system for a vessel according to claim <NUM>.

Furthermore, the invention relates to a method for retrofitting a vessel with a fluke drive system according to claim <NUM>.

In the following, the invention will be described in detail, with reference to exemplifying embodiments of the invention and to the enclosed drawings, wherein:.

All <FIG> are of principle character, and in general not drawn to scale.

Throughout this description, notions of direction, such as "up" or "down" relate, unless otherwise stated, to an operation state of the fluke driving system in which the fluke with a main fluke plane oriented substantially horizontally and the fluke moving reciprocally up and down vertically.

Hence, <FIG> illustrates a fluke drive system for a vessel <NUM> according to a first aspect of the present invention. The vessel <NUM> has a longitudinal direction D, where the arrow D in <FIG> points in a vessel <NUM> forward direction, opposite to a vessel <NUM> aft direction. It is realized that, in <FIG> and <FIG>, the vessel <NUM>, <NUM> is illustrated in a longitudinal and vertical cross-section as seen from the side of the vessel <NUM>, <NUM>.

The said drive system of <FIG> comprises a pivot element <NUM>, having a forward end and an aft end. At its forward end, the pivot element <NUM> is pivotally connected to a hull <NUM> of the vessel <NUM>. At its aft end, the pivot element <NUM> is connected to a flexible fluke <NUM>.

According to the present invention, the fluke <NUM> is forced to move reciprocally in the water below the water surface, upwards and downwards, and as a result give rise to a forward propulsion of the vessel <NUM>. The corresponding is true regarding the fluke <NUM> in the embodiment illustrated in <FIG> in relation to vessel <NUM> (see below).

Furthermore, the drive system comprises a driving mechanism having a drive point <NUM>. The driving mechanism is arranged to impart a reciprocal or rotary movement to the drive point <NUM>, so that the fluke <NUM> is driven reciprocally upwards and downwards as a result of the driving of the drive point <NUM>.

The drive system further comprises a drive rod <NUM>, having a first end (upper end in <FIG>) and a second end (lower end in <FIG>).

The drive rod <NUM> is connected, at said first end, to the drive point <NUM>. In other words, the said first end is connected to the drive point <NUM> such that the drive point <NUM> drives the first end when the drive point <NUM> moves as a result of said driving mechanism action.

The drive rod <NUM> is furthermore connected at said second end to the pivot element <NUM>. In particular, the second end is connected to the pivot element <NUM> at a point <NUM> along the pivot element <NUM> between said forward and aft ends of said pivot element <NUM>. This is clearly illustrated in the exemplifying embodiment shown in <FIG>. The point <NUM> may also be a pivot point, as is seen in <FIG>.

According to the present invention, the driving mechanism further comprises a carrier element <NUM>, fastened to a propeller axle <NUM> of the vessel <NUM>, which propeller axle <NUM> may be driven by a conventional engine <NUM>, such that the carrier element <NUM> is arranged to rotate with the said propeller axle <NUM>.

Furthermore, the said drive point is eccentrically arranged on the carrier element <NUM>, so that a rotation of the propeller axle <NUM> will drive the drive rod <NUM> back and forth (up and down in <FIG>), in turn resulting in a reciprocal up and down motion of the flexible fluke <NUM>, via the pivot element <NUM>.

In order to keep the fluke <NUM> fixed to the same vertical plane during the full range of its reciprocal movement up and down, the pivot point <NUM> may be arranged to keep a constant angle of the pivot element <NUM> in relation to a vertical plane. This may, for instance, be accomplished by the pivot point <NUM> being supported across a sufficiently long horizontal stretch across the hull <NUM>, possibly in combination with the pivot element <NUM> comprising oblique support beams connecting at different horizontal points to the pivot point <NUM>.

With the fluke drive system described above, an existing drive system, comprising an existing engine <NUM> of a vessel, having an existing propeller axle <NUM>, can be retrofitted for fluke propulsion in a way which is not only very cost-efficient, but also highly reliable in operation. Various possible details regarding such a drive system and such retrofit will be described in the following.

As can be seen in <FIG>, the vessel <NUM> typically comprises a propeller axle <NUM> stabilizing element <NUM>, such as a beam fastened to the hull <NUM> and extending to a point at which it rotationally receives and supports the propeller axle <NUM>. Such stabilizing element <NUM> is hence conventional as such, but achieves the double purpose of stabilizing the propeller axle <NUM> and providing a support against which the lever formed by the pivot element <NUM> acts when the fluke <NUM> is raised and lowered. Preferably, the propeller axle <NUM> support element <NUM> is a previously existing propeller axle <NUM> support element <NUM>, which is not modified in any way as a result of the retro-installation of a fluke drive system according to the present invention.

In some embodiments, the pivot element <NUM> is arranged in its entirety externally to said hull <NUM>. This means that no hull <NUM> through holes must be, or are in fact, provided as a result of the mounting of said pivot element <NUM>.

In particular, and as is illustrated in <FIG>, the pivot element <NUM> is pivotally connected to the pivot point <NUM>, such as comprising a bolt rotating in a through hole arranged externally to the hull <NUM>, which pivot point <NUM> is welded to an external metal surface of said hull <NUM>. Such a through hole may be arranged as a part of the pivot element <NUM> itself, or as a part that is permanently welded to the hull <NUM>. Then, such a bolt may be arranged on the other part (hull <NUM> or pivot element <NUM>, respectively).

The pivot element <NUM> itself may comprise, or be substantially comprised by, an elongate metal rod, such as a stainless steel rod with a smallest diameter of at least <NUM>.

In some embodiments, the driving mechanism is arranged, in its entirety, externally to said hull <NUM>. This means that no moving part of the driving mechanism is arranged inside the hull <NUM>, and in particular that no through holes are arranged as a part of an installation of the present driving mechanism on the vessel <NUM>, for instance during a retro-installation on an existing vessel. It is realized, however, that a through hole for the propeller axle <NUM> is of course necessary, as well as any other through holes provided for different reasons than being part of the fluke drive system according to the present invention. Such already-existing through holes are hence not considered through holes being arranged as a part of an installation of the driving mechanism according to the invention. In other words, the retro-installation of the first aspect of the present invention may be undertaken without having to provide any additional through holes through the hull <NUM> of the vessel <NUM>.

As illustrated in <FIG>, the carrier element <NUM> may advantageously be fastened to an aft end of the propeller axle <NUM>, and in particular to an already existing propeller fastening means, which propeller fastening means is then conventionally arranged to fasten a propeller to the propeller axle <NUM>. However, the propeller fastening means may not support a propeller after retro-installation of the present fluke drive system, since it is instead connected to and supports the carrier element <NUM>. Hence, the propeller axle <NUM> does in this case not support a propeller which would normally or previously have been attached to and supported by the propeller axle <NUM> for vessel <NUM> propulsion by rotation. To this end, the carrier element <NUM> may be specifically adapted with connection means, such as bolt holes of suitable dimension and placing, so as to be compatible with the existing propeller fastening means arranged on or as a part of the propeller axle <NUM>.

Alternatively, the carrier element <NUM> may be permanently fastened to the propeller axle <NUM>, such as welded thereto.

The carrier element <NUM> may be or comprise a metal disc, which disc may be substantially circular symmetric or of cylindrical shape, preferably with an axis of symmetry coaxial with a propeller axle <NUM> centre axis. In particular, the carrier element <NUM> may be fastened to or near (such as within at the most <NUM> meter of) an aft end surface of the propeller axle <NUM>.

That the drive point <NUM> is arranged eccentrically to the propeller axle <NUM> means that the drive point <NUM> will describe a circular path of motion when being driven by the driving mechanism due to the propeller axle <NUM> rotating, which circular path of motion will be circular symmetric about a propeller axle <NUM> centre axis. It is understood that the said circular path of motion will have a non-zero, possibly constant, radius (the "excentre radius"), advantageously a radius of at least <NUM>, more preferably of at least <NUM>. The said radius may also be at the most <NUM>.

In some embodiments, the carrier element <NUM> comprises an excentre radius adjustment means, arranged to be remote controlled to adjust said excentre radius of the drive point <NUM> in relation to the rotation axis of the propeller axle <NUM>.

<FIG> illustrates, in a simplified view as seen from the aft end of the vessel <NUM> looking forward, a carrier element <NUM> which may be used to this end. More particularly, the excentre radius adjustment means illustrated in <FIG> comprises a hydraulic cylinder (part of <NUM>) connected at one point (<NUM>) to the carrier element <NUM> and at an opposite point (<NUM>) to the above-mentioned first end of the drive rod <NUM>.

Hence, and as can be seen in this <FIG>, the carrier element <NUM> may be concentrically oriented to the propeller axle <NUM>. A track or guide <NUM> may be arranged in the carrier element <NUM>, such as following a straight, possibly radial, path. A track following part <NUM> arranged at a distal end of an excentre radius adjustment hydraulic cylinder arrangement <NUM> may be arranged to be displaced along the track <NUM> in response to an activation of the arrangement <NUM>, which activation hydraulically changes the length of the hydraulic cylinder in question. At an opposite, proximate end of the arrangement <NUM>, a pivotal connection <NUM> to the carrier element <NUM> may be arranged, acting as a fixed point in relation to which the track following part <NUM> moves. Then, the above discussed drive point <NUM> is, or is attached to, the track following part <NUM>.

As a consequence, the excentre radius of the drive point <NUM>, in other words the distance between the drive point <NUM> and the propeller axle <NUM> centre axis, can be adjusted by hydraulically adjusting the length of the arrangement <NUM>. Such hydraulic adjustment may be imparted remotely, such as using a control means provided at the captain's deck of the vessel <NUM> in turn connected to a suitably hydraulic pressure activation means connected to the arrangement <NUM>.

By varying the said excentre radius, the stroke amplitude of the fluke <NUM> can be adjusted, hence affecting a propulsion power of the vessel <NUM>. This is particularly an important feature when providing a drive system according to the present invention as a post-installation to an already existing vessel, having an already existing drive system comprising the engine <NUM> and the propeller axle <NUM>. Namely, when such an existing propeller axle <NUM> is used for propulsion using the fluke <NUM>, it may not always be desirable or possible to reach a full desired propulsion power interval merely by adjusting the engine <NUM> power. By alternatively or additionally adjusting the fluke <NUM> stroke amplitude, the possible control range in terms of propulsion power becomes more flexible. For instance, it is possible to adjust the propulsion power while maintaining the same propeller axle <NUM> rotation velocity.

In the embodiment illustrated in <FIG>, and in other embodiments, the excentre radius adjustment means may be arranged to adjust the said excentre radius across an allowable excentre radius interval, such as a continuous interval. This excentre radius interval may be outwards limited, defining a maximum fluke <NUM> stroke amplitude. Such a maximum fluke amplitude may, in this first but also in the second aspect of the present invention described below, preferably be at least <NUM> meters, preferably at least <NUM> meters, and preferably at the most <NUM> meters, preferably at the most <NUM> meters. It is noted that the movement of a fluke <NUM>; <NUM> connection point to the pivot element <NUM>; <NUM> is substantially vertical (as a result of the longitudinal direction D length of the pivot element <NUM>; <NUM> in relation to the stroke length of the drive rod <NUM>; <NUM> and the location of the connection point <NUM>; <NUM>), and that it is this vertical movement to which the "fluke amplitude" mentioned herein refers.

Moreover, the said excentre radius interval may also comprise a point, such as an inner extreme point, at which the excentre radius is so small so that the fluke <NUM> is substantially not driven as a result of a rotation of the propeller axle <NUM>. Hence, at this interval point, the fluke <NUM> stroke amplitude is substantially zero, so that the fluke <NUM> is substantially still even under rotation of the propeller axle <NUM>. This provides a convenient way of turning off the fluke <NUM> propulsion without having to switch off the engine <NUM>. In the case where the propeller axle <NUM> comprises a propeller in addition to the drive mechanism described here, this also provides a way of quickly and conveniently switching fluke <NUM> propulsion on and off, without having to switch propeller propulsion on or off at the same time.

<FIG> illustrates a fluke drive system according to a second aspect of the present invention. The fluke drive system of <FIG>, like the one illustrated in <FIG>, is for a vessel <NUM> with a longitudinal direction D.

The fluke drive system comprises a pivot element <NUM>, corresponding to pivot element <NUM> and having a forward end and an aft end. The pivot element <NUM> is pivotally connected at its forward end to the hull <NUM> of the vessel <NUM>, and at its aft end to a flexible fluke <NUM>, corresponding to fluke <NUM>. The forward end of the pivot element <NUM> is connected to pivot point <NUM>, corresponding to pivot point <NUM>, welded to the hull <NUM> without requiring hull <NUM> penetrations.

The drive system of <FIG> also comprises a driving mechanism having a drive point <NUM>, which driving mechanism is arranged to impart a reciprocal or rotary movement to the drive point <NUM>.

The drive point <NUM> corresponds to drive point <NUM>. As can be seen from <FIG>, the drive point <NUM> describes a rotary movement when driven by the drive system, whereas in <FIG> the drive point <NUM> describes a linear, reciprocal movement when driven. This serves to show two different example of such reciprocal or rotary movement. However, in the drive system of <FIG> a linear, reciprocal movement can be used also, by providing a suitable lever system translating the rotary motion of the propeller axle <NUM> to a vertically oriented, linearly reciprocal movement of the drive point <NUM>. Furthermore, in <FIG> a rotary drive point <NUM> movement can be provided by an inverse function, translating the linearly reciprocal movement of the hydraulic drive rod <NUM> (see below) to a rotating movement in a per se conventional manner. It is realized that there are many additional possibilities to achieve such linear or rotational movements of the drive points <NUM>, <NUM>.

The <FIG> drive system further comprises a drive rod <NUM>, corresponding to drive rod <NUM>, having a first end and a second end, which drive rod <NUM> is connected, at its first end, to the drive point <NUM>, and at its second end to the pivot element <NUM>. In particular, the said second end is connected to the pivot element <NUM> at a point <NUM> along the pivot element <NUM> between said forward and aft ends of the pivot element <NUM>.

It is realized that in the second aspect illustrated by way of example in <FIG>, the drive point <NUM> may be a part of the drive rod <NUM>, being driven hydraulically back and forth. This way, the drive point <NUM> is "connected to" the drive rod <NUM> for forced reciprocal movement, in that the drive point <NUM> will be forcibly moved by the hydraulic pump <NUM> pressure, resulting in the entire drive rod <NUM> moving. Alternatively, one may in this case simply say that the hydraulic pump <NUM> hydraulically drives the drive rod <NUM> in a reciprocal manner.

So far, the drive system according to the first aspect is similar to the drive system according to the second aspect.

However, as is illustrated in <FIG>, the driving mechanism in this second aspect comprises a hydraulic pump <NUM>, arranged to be driven by the propeller axle <NUM> of the vessel <NUM>, such that the force provided by the rotation of the propeller axle <NUM> is harvested and converted into a hydraulic pressure in the hydraulic pump <NUM>.

Furthermore according to the second aspect, the said drive point <NUM> movement is achieved using said hydraulic pressure achieved by said hydraulic pump, so that a rotation of the propeller axle <NUM> will drive the drive rod <NUM> back and forth (upwards and downward in <FIG>), in turn resulting in a reciprocal up and down motion of the flexible fluke <NUM> in a way corresponding to the above-described reciprocal up and down motion of the flexible fluke <NUM> described above.

The hydraulic pump <NUM> is arranged with a rotary energy conversion mechanism <NUM>, such as a conventional gear/lever system, for converting said rotary energy from the propeller axle <NUM> into said hydraulic pressure as an overpressure to the hydraulic pump <NUM>. Such conversion mechanism <NUM> is well-known in the art, and will not be described in detail herein.

The pump <NUM> may provide a hydraulic pressure to the drive point <NUM> (which may be a conventional hydraulic piston or plunger) for driving the drive rod <NUM>. This hydraulic pressure may vary with the same frequency as the rotation frequency of the propeller axle <NUM>. However, it may also vary according to a different frequency, which may be freely remote controlled by a user so as to vary a fluke <NUM> propulsion frequency and as a result possibly also propulsion power. Furthermore, the hydraulic pump <NUM> makes it possible to vary the stroke length of the drive rod <NUM> across an allowable interval corresponding to the above-described excentre radius interval. Such control may also take place in a remote controlled manner.

Hence, an existing engine <NUM>, corresponding to engine <NUM>, is used to propel the existing propeller axle <NUM>, which in turn provides energy for the hydraulic pump <NUM> to build up a hydraulic pressure for propelling the fluke <NUM>.

According to a preferred embodiment, the hydraulic pump <NUM> is completely arranged inside the interior of said hull <NUM>. This provides for a less aggressive operation environment for the hydraulic pump <NUM>, and also for simpler access to maintenance. However, the hydraulic pump <NUM> may also be arranged in its entirety externally to the hull <NUM>, in which case no through hole must be provided in the hull <NUM> for accommodating the drive rod <NUM> (which is necessarily the case in the design illustrated in <FIG>). It is particularly noted that the hydraulic pump <NUM> may convert the rotational energy from the propeller axle <NUM> from a point along the propeller axle <NUM> externally to the hull <NUM>, and then drive the drive rod <NUM> (which is then also completely arranged externally to the hull <NUM>) from a point also located outside of the hull <NUM>.

As mentioned, the drive rod <NUM> itself may be hydraulically driven, such as directly driven by the hydraulic pressure supplied by the hydraulic pump <NUM> via suitable hydraulic conduits, and furthermore installed in and through a through hole <NUM> through the said hull <NUM>.

As also mentioned above, the propeller axle <NUM>; <NUM>; <NUM> may also support a propeller. An example of such a configuration is illustrated in <FIG>, where a propeller comprising propeller blades <NUM> is shown on the propeller axle <NUM>. In this case, the propeller may comprise a remote controllable blade folding mechanism <NUM>, arranged to allow a user to remotely control said propeller blades <NUM> to fold (broken lines) and unfold (full lines) so as to control the propelling power applied by the propeller in question. Such remote controlling may be imparted, for instance, in a way corresponding to the above-described hydraulically remote operated pivot element <NUM> amplitude control mechanism.

A foldable propeller can also be used as a backing function for a propeller axle connected to a fluke. In this case, the propeller blades are arranged to propel the vessel in an aft direction when the propeller axle in question rotates. Normally, when the fluke in question is driven for vessel forward propulsion, the propeller blades are folded in. however, when the vessel needs to back, the propeller blades are remotely folded out. Then, the propeller blades are designed so that they provide a backwards propulsion force which at least exceeds a forwards propulsion force as the fluke is moved up and down by the same propeller axle. To achieve this, the fluke stroke amplitude may temporarily be remotely adjusted down during such backing.

In <FIG>, a carrier <NUM> with a drive rod <NUM> are also shown, corresponding to carrier <NUM> and drive rod <NUM>, respectively. As is illustrated in <FIG>, in this case the carrier <NUM> is arranged aft of the propeller, so that the drive rod <NUM> does not interfere with the propeller axle <NUM> as the latter rotates.

Also shown in <FIG>, the propeller blades <NUM> are arranged to fold in a forward direction. However, it is realized that they may also be arranged to fold in an aft direction, depending on embodiment.

<FIG> illustrates, in a top view, a fluke <NUM> of a type generally useful with the present invention. Hence, the fluke <NUM> corresponds to flukes <NUM>; <NUM>.

Preferably, the fluke <NUM> is made from a flexible solid (or partly hollow) material, such as a rubber or other polymer based material with sufficient durability yet offering flexibility for increased power transmission when used as described above, for propelling a vessel <NUM>, <NUM> using reciprocal up- and down movements under water. Examples of suitable such materials comprise rubber, polyurethane and similar materials.

As is illustrated in <FIG>, the fluke <NUM> may have flexible steel inserts <NUM> at one or several locations, such as extending along its periphery and/or its centreline. Such inserts <NUM> may, for instance, be made from spring steel. The inserts <NUM> may be removable and replaceable, for adjustment of the fluke <NUM> flex properties after installation. This may, for instance, be useful to adapt the properties of the fluke <NUM> after a change in vessel <NUM>, <NUM> load or engine <NUM>, <NUM>.

In an alternative or additional embodiment, the fluke <NUM> comprises a remote controlled hydraulically or pneumatically operated, preferably passive, stiffening system <NUM>. In this case, the reference numeral <NUM> does not denote steel inserts (as described above), but hydraulic or pneumatic channels. Then, the hydraulic or pneumatic channels <NUM> are arranged to make the fluke <NUM> stiffer as a result of a supplied higher hydraulic or pneumatic pressure to the channels <NUM> via the stiffening system <NUM>, and vice versa. This will allow the vessel <NUM>, <NUM> to dynamically alter the properties of the fluke <NUM>; <NUM> in response to varying operation prerequisites.

It is realized that the stiffening system <NUM>, as well as the above-described propeller folding system <NUM> and the remote fluke <NUM> amplitude adjustment system <NUM>, may be provided with a suitable hydraulic pressure from a hydraulic pump such as the pump <NUM>, or in any other way, and may be provided with remote control means such as remote controlled valves arranged inside the hull <NUM>; <NUM> near the hydraulic pump in question for easy remote control action and maintenance.

As mentioned previously, the present invention is particularly well-suited for large vessels, such as tankers and freight ships. Preferably, the vessel is a larger PWC (Personal Water Craft), or even more preferably a cargo or freighter ship, and preferably has a DWT (DeadWeight Tonnage) of at least <NUM>, preferably at least <NUM>, more preferably at least <NUM>,<NUM>, most preferably at least <NUM>,<NUM>.

For such large vessels, it has previously turned out to be difficult to provide fluke propulsion in a cost-efficient and reliable way.

The large vessel <NUM>; <NUM> may then comprise an internal engine <NUM>; <NUM>, such as a conventional ship diesel engine, arranged to drive the propeller axle <NUM>; <NUM> at a maximum of <NUM> RPM, preferably at a maximum of <NUM> RPM. Then, it is very advantageous to allow the driving mechanism of the present system to be arranged to impart the above described reciprocal or rotary movement to the drive point <NUM>; <NUM> at the same frequency as the rotation of the propeller axle <NUM>; <NUM>. This way, no gears or other mechanical means for rotational velocity adaptation are necessary, leading to a very simple, robust and reliable construction.

For such large vessels, and in particular for such slow propeller axle <NUM>; <NUM> rotational frequencies, it is preferred that the pivot element <NUM>; <NUM> is between <NUM> and <NUM> meters of length, and that the fluke has a horizontal projection surface of at least <NUM><NUM>, preferably of at least <NUM><NUM>, and at the most <NUM><NUM>, preferably at the most <NUM><NUM>. For large horizontal projection surfaces of at least <NUM><NUM>, fluke swing frequencies of at the most <NUM> RPMs will typically be useful.

In case there are several propeller axles on the vessel <NUM>; <NUM>, each such propeller axle is preferably provided with a respective fluke each, with an individual fluke drive using the respective rotary motion of its respective propeller axle as an energy source.

Hitherto, the vessel <NUM>, <NUM> has been described as a floating vessel. However, it is realized that the present invention can also be applied to submarine vessels, as long as the fluke is provided so that it can perform said reciprocal vertical motion entirely below the water surface.

<FIG> illustrates a third aspect of the present invention, namely a fluke <NUM> drive system comprising a fluke connecting part <NUM> constituting the connecting element between the pivot element <NUM>; <NUM> and the fluke <NUM>; <NUM>. The fluke connecting part <NUM> is useful with the fluke drive systems according to the above-described first and second aspects, as well as with other fluke drive systems.

As described above, such a fluke drive system comprises a flexible fluke <NUM> and a fluke driving mechanism (not illustrated in detailed in <FIG>) in turn comprising a displacement means <NUM> arranged to be driven to move reciprocally upwards and downwards. In <FIG>, the displacement means <NUM> corresponds to the pivot element <NUM>; <NUM> described above.

The fluke <NUM> is hence connected to the displacement means <NUM> via the fluke connecting part <NUM>.

According to this third aspect of the present invention, the fluke connecting part <NUM> comprises a pivot joint <NUM>, pivotally connecting a first point a of the displacement means <NUM> to a second point b of the fluke <NUM>. In <FIG>, this first point a is arranged on a first pivot part <NUM> of the fluke connecting part <NUM>, which first pivot part <NUM>, since it is rigidly connected to the displacement means <NUM>, is considered part of the displacement means <NUM>. The second point b is arranged on a second pivot part <NUM> of the fluke connecting part <NUM>, and the second pivot part <NUM>, since it is rigidly connected to the fluke <NUM>, is similarly considered part of the fluke <NUM>.

Hence, the first <NUM> and second <NUM> pivot parts are pivotally connected by the pivot joint <NUM>; the first pivot part <NUM> is rigidly connected to the displacement means <NUM>; and the second pivot part <NUM> is rigidly connected to the fluke <NUM>. It is noted that the first a and second b points are those actually directly interconnected by the pivot joint <NUM>, even though other points on the displacement means <NUM> and the fluke <NUM>, respectively, are also interconnected in a pivoting manner. In particular, points a and b may both be aligned with a pivot axis of the pivot joint <NUM>.

The fluke connecting part <NUM> further comprises an upper spring means <NUM>, connecting a third point c of the displacement means <NUM> (and actually of the first pivot part <NUM>) to a fourth point d of the fluke <NUM> (and of the second pivot part <NUM>). The third point c is arranged above the first point a, while the fourth point d is arranged above the second point b. Preferably, the upper spring means <NUM> is located above the first a and second b points, such as entirely above these points a and b.

Similarly, the fluke connecting part <NUM> also comprises a lower spring means <NUM>, connecting a fifth point e of the displacement means <NUM> (and the first pivot part <NUM>) to a sixth point f of the fluke <NUM> (and the second pivot part <NUM>). The fifth point e is arranged below the first point a, and the sixth point f is arranged below the second point b. Preferably, the lower spring means <NUM> is located below the first a and second b points, such as entirely below these points a and b.

Hence, the fluke <NUM> is suspended on the displacement means <NUM> via the pivot joint <NUM>, allowing the fluke <NUM> to perform pivoting movements in a non-horizontal, preferably vertical or substantially vertical, plane. Preferably, the pivot joint <NUM> also limits the fluke <NUM> to only such movements. These pivoting movements will take place under the influence of spring forces from the said spring means <NUM>, <NUM>. These spring means <NUM>, <NUM> may be configured so that they together are arranged to bring the fluke <NUM> to a relaxed state in which the fluke <NUM> is substantially vertically oriented, or somewhat slanting upwards in the aft direction. In this state, both spring means <NUM>, <NUM> may be slightly stretched but counterbalancing each other. So in order to pivot upwards or downwards, the fluke <NUM> must stretch one of the spring means <NUM>, <NUM> while pushing the other spring means towards a more relaxed state.

Furthermore, the spring means <NUM>, <NUM> may together be configured so that a certain resistance must be overcome in order for the fluke <NUM> to pivot upwards, and a certain other resistance must also be overcome to pivot downwards from said relaxed state, so that the fluke <NUM> is brought back to the relaxed state when not affected by any external force.

Such a fluke <NUM> suspension has proven to provide excellent mechanical energy transfer efficiency in terms of transforming reciprocal vertical displacement means <NUM> movements to fluke <NUM> forwards propulsion power. The fluke connection part <NUM> will impart a "wavy" type movement of the fluke <NUM> as a result of an upwards/downwards reciprocal movement of the displacement means <NUM>, which hence leads to high propulsion energy efficiency.

In preferred embodiments, the said pivot joint <NUM>, the upper spring means <NUM> and the lower spring means <NUM> are the only mechanical connections between the displacement means <NUM> to which the fluke <NUM> is connected and the fluke <NUM> itself. In particular, these connections <NUM>, <NUM>, <NUM> may be the only mechanical connections affecting the mechanical behaviour of the fluke <NUM> in relation to the fluke driving mechanism.

The spring means <NUM>, <NUM> may both be tension springs, such as coil springs made from stainless spring steel. They may also be gas springs with corresponding properties. There may also be several upper and/or lower spring means, of the same or different types, as long as the basic properties described herein of the fluke connecting part <NUM> are achieved.

In some embodiments, the spring constant of the upper spring means <NUM> is larger, such as at least twice, the spring constant of the lower spring means <NUM>. This results in that it will require more force to pivot (about point <NUM>) the fluke <NUM> downwards than upwards, affecting how the fluke <NUM> moves in the water when being pushed (by the displacement means <NUM>) upwards and downwards. In general, the fluke <NUM> will, when moving up and down in the water, have a smaller downwards pivot angle (about point <NUM>, achieved by the fluke pressing water upwards) in relation to the horizontal when being pushed with a certain vertical force upwards by the displacement means <NUM>, and with a larger corresponding upwards pivot angle to the horizontal when being pushed with an equal vertical force downwards by the displacement means <NUM>. Such movement pattern has proven to provide a very efficient energy transfer, as well as minimized non-desired vessel <NUM>, <NUM> up/down movements, for forward fluke <NUM> propulsion in water.

In some embodiments, the fluke is freely movable, against the spring force of said spring means <NUM>, <NUM> across an angular interval of ±<NUM>° in relation to the horizontal.

The said first a, third c and fifth e points may all be rigidly connected to each other, such as via the first pivot part <NUM>. Similarly, the second b, fourth d and sixth f points may all be rigidly connected to each other, such as via the second pivot part <NUM>.

Using a fluke drive of the type described herein to propel a vessel may provide a propulsion power which may not correspond to an existing or standard rudder of the vessel. This is particularly the case where an existing engine <NUM>; <NUM> is used with a retrofitted fluke drive system as described herein, and further particularly in cases where an existing propeller is to be used together with such a retro-installed fluke drive system.

To this end, in some embodiments the vessel <NUM>; <NUM> may further be retrofitted with a rudder aggregate such as the one illustrated in <FIG>. In this case, the fluke drive system according to the invention comprises, in addition to a previously existing main rudder <NUM>, also one or several additional rudders <NUM>, <NUM>, fastened in parallel to the main rudder <NUM> on either sides of said main rudder <NUM>, such as via two or more retro-installed beams <NUM>. The additional rudders <NUM>, <NUM> are then connected to a previously existing rudder steering mechanism, such as via a direct mechanical connection to the main rudder <NUM>, so that they are moved in concert with the main rudder <NUM> such that they will always be arranged substantially in parallel to the main rudder <NUM> when a user controls the main rudder <NUM> via the conventional and existing vessel steering mechanism.

Preferably, the additional rudders <NUM>, <NUM> may be locally connected to the main rudder <NUM> so as to be forced to move in a corresponding manner as the main rudder moves <NUM>. Such a local connection may be via said beams <NUM>. It is realized that <FIG> is simplified, but one of ordinary skill in the art will be able to design a suitable lever system to achieve such controlled movement of the additional rudders <NUM>, <NUM>. Furthermore, the additional rudders <NUM>, <NUM> may be smaller, such as not extending as far in the aft direction, as the main rudder <NUM>, and they may also be arranged symmetrically on either side in relation to the main rudder <NUM>.

<FIG> is a flow chart illustrating a method according to the present invention, for retrofitting a vessel <NUM>; <NUM> with a fluke drive system of the type described above.

In a different step, the pivot element <NUM>; <NUM> is provided to the vessel <NUM>; <NUM>, the pivot element <NUM>; <NUM> having a forward end and an aft end, as described above, and being connected at the aft end to the flexible fluke <NUM>; <NUM>. This pivot element <NUM>; <NUM> provision step also includes connecting the pivot element <NUM>; <NUM> at the said forward end to the hull <NUM>; <NUM> of the vessel <NUM>; <NUM>.

In a different step, the driving mechanism is provided, which driving mechanism has said drive point <NUM>; <NUM>. As described above, said driving mechanism is provided for imparting a reciprocal or rotary movement to the drive point <NUM>; <NUM> in question.

In case a drive system according to the first aspect is installed, this driving mechanism provision step also comprises the carrier element <NUM> being fastened to the existing propeller axle <NUM> of the vessel <NUM> so that the carrier element <NUM> rotates with the said propeller axle <NUM>. Further in a retro-installation according to said first aspect, in this same driving mechanism provision step, the said drive point <NUM> is also eccentrically arranged on the carrier element <NUM> so that a rotation of the propeller axle <NUM> will drive the drive rod <NUM> back and forth as described above, in turn resulting in a reciprocal up and down motion of the flexible fluke <NUM>.

If, on the other hand, a drive system according to the said second aspect is being retro-installed, the driving mechanism provision step may instead comprise providing the hydraulic pump <NUM>, arranged to be driven by the propeller axle <NUM> of the vessel <NUM>; and the same step may also comprise installing the hydraulic pump <NUM> so that a hydraulic pressure achieved by the hydraulic pump <NUM> in turn achieves said movement of the drive point <NUM> as described above, so that a rotation of the propeller axle <NUM> will drive the drive rod <NUM> back and forth, in turn resulting in a reciprocal up and down motion of the flexible fluke <NUM>.

In a different step, the drive rod <NUM>, <NUM> is provided, having a first end and a second end as described above. This step includes connecting the drive rod <NUM>; <NUM> at the first end to the drive point and at the second end to the pivot element <NUM>; <NUM>. More particularly, the said second end of the drive rod <NUM>; <NUM> is connected to the pivot element <NUM>; <NUM> at a point along the pivot element <NUM>; <NUM> between said forward and aft ends of the pivot element <NUM>; <NUM>, as described above.

At a subsequent step, the method ends. It is realized that the above intermediate steps may be taken in any order, or simultaneously.

It is realized that additional steps may also be comprised in such a retro-installation method, including installing an excentre radius adjustment means <NUM>; adjusting the size, shape and properties of the fluke <NUM>, including providing it with metal inserts <NUM> and/or a hydraulic stiffening system of the above described type; providing the fluke <NUM> with a fluke connecting part <NUM> of the above described type; and installing additional rudders <NUM>, <NUM> of the type illustrated in <FIG>. All these steps are then performed in accordance with that which has been described above.

Furthermore, the retro-installation method may comprise installing several fluke drive systems on the same vessel <NUM>; <NUM>, driving several flexible flukes of the above described types; or installing at least one fluke drive system of the above described type arranged to drive several flukes on the same vessel <NUM>; <NUM>. For instance, one single hydraulic pump <NUM> may be arranged to provide hydraulic pressure to impart movement to several drive rods <NUM>, each moving a respective pivot element <NUM> with a respective fluke <NUM>. Also, on one and the same vessel <NUM>; <NUM>, fluke drive systems according to both the first and the second aspects may be installed concurrently.

It is highly preferred that the vessel <NUM>; <NUM> in question is of the above described, large, type, and that the installation is a true retro-installation. This means that the engine <NUM>; <NUM> is an existing propulsion engine of the vessel in question <NUM>; <NUM>, and also that the propeller axle <NUM>; <NUM> is an existing propeller axle driven by the engine <NUM>; <NUM> in question. It is preferred that no additional propeller axle support beams in addition to existing ones <NUM> are retro-installed.

The retro-installation method may also comprise a remote control connecting step, in which remote control means, such as control cabling or control hydraulics, are installed so as to allow a user to remote control the retro-installed functionality as described above. Such remote controlling may, for instance, then take place from the captain's bridge.

In <FIG> and <FIG>, the pivot element <NUM>; <NUM> is arranged vertically below the propeller axle <NUM>; <NUM>. Although this is typically the case, it is realized that the pivot element <NUM>; <NUM> may also be arranged vertically above the propeller axle <NUM>; <NUM>.

All which has been said in relation to the respective fluke drive systems of the first, second and third aspects, including what has been said regarding individual component parts of these systems, are equally applicable to the other aspects of the invention, as far as they are compatible. Furthermore, all which has been said in relation to the installation methods is equally applicable to the corresponding fluke drive system, and vice versa.

Claim 1:
Fluke drive system for a vessel (<NUM>), comprising
a pivot element (<NUM>) having a forward end and an aft end, which pivot element (<NUM>) is arranged in its entirety externally to said hull (<NUM>) and pivotally connected at the forward end to a hull (<NUM>) of the vessel (<NUM>) and which pivot element (<NUM>) is connected at the aft end to a fluke (<NUM>;<NUM>;<NUM>);
a driving mechanism having a drive point (<NUM>;<NUM>), which driving mechanism is arranged to impart a reciprocal or rotary movement to the drive point (<NUM>;<NUM>); and
a drive rod (<NUM>) having a first end and a second end, which drive rod (<NUM>) is connected at the first end to the drive point (<NUM>;<NUM>),
wherein the driving mechanism comprises a carrier element (<NUM>;<NUM>) fastened to a propeller axle (<NUM>;<NUM>;<NUM>) running through the hull (<NUM>) of the vessel (<NUM>) and being arranged to rotate with the said propeller axle (<NUM>;<NUM>;<NUM>), wherein the said drive point (<NUM>;<NUM>) is eccentrically arranged on the carrier element (<NUM>;<NUM>) so that a rotation of the propeller axle (<NUM>;<NUM>;<NUM>) will drive the drive rod (<NUM>) back and forth, in turn resulting in a reciprocal up and down motion of the fluke (<NUM>;<NUM>;<NUM>), characterised in that the fluke (<NUM>;<NUM>;<NUM>) is a flexible fluke, in that a second end of the drive rod (<NUM>) is connected to the pivot element (<NUM>) at a point (<NUM>) along the pivot element (<NUM>) between said forward and aft ends, and in that the pivot element (<NUM>) is pivotally connected to a pivot point (<NUM>) which is welded to the said hull (<NUM>).