Field of invention

The present invention relates to a propulsion system for a marine vessel wherein the employed means for propulsion include rotatable fins with their axis held substantially normal to the hull surface, and wherein those fins translate in a mostly submerged, not purely circular, endless path along the surface of the hull. As additional characterizations, a significant part of the said path lies substantially perpendicular to the direction of the flow of water that surrounds the vessel, and the said rotation axes of the fins are also sub- stantially perpendicular to the endless path.

In one embodiment, the propulsion system we relate to could resemble a large, actuated, transversal, endless chain held flush with the hull across a barge stern, chain-wheels laying flat and flush with the hull, with fins articulated on the hinges of the chain segments; the atwartships movement of the fins held at the proper rotation angle creates the propulsive force, with one row of fins moving to port, and one row of fins moving to starboard.

According to one aspect, the invention relates to a maritime vessel comprising a hull having an opening through which a propulsive system extends at least partially. The propulsive system comprises at least one sealing member that contains a number of sealing segments that separate the sea from the volume in the hull. It is understood that the hull in this sense includes the hull structure and all parts that are connected to it and that do not contribute actively to the thrust necessary for propulsion of the ship.

The sealing member has segments with part of its surface that faces the inte- rior of the vessel and another part that faces the exterior of the vessel.

The segments of the sealing member allow the propulsive fins to protrude from the hull while moving about in their endless path, and the said segments move in an endless path that is conjugated with the endless path of the propulsive fins.

Mountings allow the segments of the sealing member to move at least in two directions along their endless path, and may allow segments to move in a direction outside the surface determined by the endless path as well.

Mountings also allow the pressure forces exerted by the sea to be transmitted to the hull either directly or through the propulsion system, and may guide pressure waves or impact forces to by-pass most of the propulsion system.

It must be understood that the hull of the ship accommodates the complete propulsion system, the sealing member and all necessary technical means. If the propulsive system were to be mounted within a large rudder, in this text, the rudder would be understood as being part of the hull.

Background

An important objective of ship designers for new ships is to achieve low fuel consumption compared to ships with a similar functionality.

It is recognised from hydrodynamics (Prandtl) that the boundary layer of a ship constitutes a layer of water of increasing speed when nearing the hull as seen from an observer immobile in the water, and that the thickness of that boundary layer increases from the fore-sections towards the aft-sections of the ship.

It is also recognised that, from an energetic point of view, an optimal marine propulsor makes maximum use of the speed gradient in the boundary layer, that is to say, it should exert the largest possible proportion of its propelling force in the part of the flow that has highest speed as seen from an immobile observer, or that has the lowest speed as seen from the ship. This is akin to a jogger running with low exertion on a band with forward speed in an airport who has the same total speed as another jogger running at higher exertion in the same direction on an immobile floor. For ships, this effect is called 'wake fraction' in the art, and is part of a larger concept called 'hull efficiency' that reflects the interaction between a propeller and the hull it propels.

In modern single-screw merchant ships, propellers make maximum use of the energy of the boundary layer ('high hull efficiency') by being put in the wake of a central skeg in the aft of the ship that directs the boundary layer towards the propeller. Some double-screw propellers utilise the same approach in wide ships. This approach is well proven. It is also well known that the attainable propulsive efficiency with this approach is limited in practice. As an example for a container feeder vessel, a very good propeller typically has open water efficiency in the vicinity of 67%, with a hull efficiency of about 108%, resulting in a total propulsive efficiency of about 73%. This percentage provides a picture that improvements of the order of 27% would be possible with an ideal propulsor. Some authors would argue that even better results would then be possible due to a narrow definition of the notion of propulsive efficiency in the industry.

Several authors have pointed to the fact that a better utilisation of the boundary layer could lead to substantial efficiency improvements, but no practical solutions have been adopted widely by the industry to date as the rotating propeller propulsion device. The present invention relates to such a propulsion system for a marine vessel: the employed means for propulsion include rotatable fins with their axis held substantially normal to the hull surface, and those fins translate in a mostly submerged, not purely circular, endless path along the surface of the hull. As additional characterizations, a significant part of the said path lies substantially perpendicular to the direction of the flow of water that surrounds the vessel, and the said rotation axes of the fins are also substantially perpendicular to the endless path.

The sealing member invention, described in this document, solves the problem on how to seal a machine and its fins that equip a ship with a propulsor that operates optimally in the boundary layer by means of fins that follow an endless track as described. This sealing function allows separation of the technical volume of the ship from the sea or separation of the inside of the ship from the sea, with obvious functional, technical and safety advantages. Background art

Propulsion by means of translating and rotating fins on an endless track with a substantial part of their path being substantially perpendicular to the flow around the ship possesses attractive features such as a higher efficiency than a rotating propeller 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 better utilisation of the boundary layer which reduces impulse losses, lowers hydrodynamic friction losses, lowers induced drag losses and lowers the drag of the hull itself. The higher efficiency results in either lower fuel consumption, and thereby possibly lower installed power for the prime-movers, or a higher service speed with the same installed propulsion power and fuel consumption.

US patent no 5,401 ,196 published march 28, 1995 (Triantafyllou et al.), French patent FR 2898580 filed 14.3.2006 (Pyre), and US 2010291814 "Fin propulsion apparatus", with priority date 2007-12-10 (Vermeiden) all disclose a propulsion systems employing flapping foils with oscillatory translation on a substantially straight path. Sealing of fins that translate in a straight path, and rotate around an axis substantially perpendicular to that path can be done with a translating plate as shown in a patent application WO 2009074581 , "sealing for fin propulsion", with priority date 2001-12-10 (Vermeiden). That invention however does not show how to seal fins that translate and rotate along an endless path, because the proposed sealing plate in that invention does not allow for the necessary permanent variation of geometry of the set of fin-stems that would cross the plate. That invention also does not provide a solution to deal with high energy forces-spikes from the sea that would originate from shocks of immerged objects or wave-slamming.

US patent application WO8810207, filed 29.12.88 "propellers" (Mistry) is one of the patents describing solutions for a class of marine propulsors with rotat- ing fins placed with their rotation axis at a fixed radius from the axis or a rotating disk. These propulsors are often called cycloidal or trochoidal propulsors and the most commonly applied of such systems is the Voith Schneider propeller on tugs and ferries. Sealing solutions for such a system are well known and straightforward to realise because of conformal surfaces with fixed geometry.

US patent US 6435827 dated 20.8.2002 "apparatus for generating a fluid flow" (Steiner) described an approach to thrust generation in a fluid in an endless path largely perpendicular to the direction of thrust but do not describe in any way how to address sealing issues when placed in a marine environment.

DE 398832 A discloses a maritime vessel including a hull having an opening through which propulsive means extend. The propulsive means is configured as a drive moving transverse to the longitudinal orientation of the maritime vessel. Prior art has so far not solved the problem of how to seal a propulsion system for a marine vessel wherein the employed means for propulsion include rotable fins with their axis held substantially normal to the hull surface, and wherein those fins translate in a mostly submerged, not purely circular, endless path along the surface of the hull, and where as additional characteriza- tions, a significant part of the said path lies substantially perpendicular to the direction of the flow of water that surrounds the vessel, and the said rotation axes of the fins are also substantially perpendicular to the endless path. Brief description of the invention

It is an objective of the present invention to set forth a propulsive system which, in an operational manner, generally will increase the overall efficiency of a maritime vessel's propulsive system. This is achieved by allowing a mari- time vessel to be propelled by means of rotable fins that translate in a non- circular endless path that extend through an opening which is covered by a sealing member having segments that follow the fin-stems in their endless path.

This sealing member separates the outside environment of the ship and the interior of the ship. This separation reduces the part of the mechanism that needs to operate in sea-water and thereby reduces viscous losses and increases operational reliability and safety.

The sealing system relates to a marine propulsion system wherein the employed means for propulsion include rotatable fins with their axis held sub- stantially normal to the hull surface, and wherein those fins translate in a mostly submerged, not purely circular, endless path along the surface of the hull, and where as additional characterizations, a significant part of the said path lies substantially perpendicular to the direction of the flow of water that surrounds the vessel, and the said rotation axes of the fins are also substan- tially perpendicular to the endless path. The opening created by the translating stems of the propulsive means, and that needs to be addressed by the sealing member, is non-convex, large relative to the ship and very large relative to common openings as placed for e.g. piping.

Sealing off the inside of the ship from the outside marine environment in such a system without causing substantial mechanical friction losses, without causing substantial hydrodynamic drag, without compromising reliability and safety, and keeping the sealing functional in the event of high-energy impact of submerged bodies or of impacting waves is a challenging problem that has not been solved before, but is worthwhile solving because of the possibility of higher overall efficiencies when compared to propeller-drive.

The sealing difficulty is compounded by the fact that the translating speeds of the fins is of the order of 10m/s, the pressure-force on the sea! can be of the order of 100kN/m2, and the opening-size to be covered by the sealing member is directly related to the ship-width as the propulsor will usually cover a large portion of the ship width.

The need for a unique sealing system is therefore clear.

In all embodiments, the sealing body includes a series of solids that jointly cover the non-convex opening in the hull and that rotate relatively to each other in the portions of the path of the propulsive means that are not straight.

According to one embodiment, some segments of the sealing member transmit a material part of the propulsive power to the propulsive means

According to one embodiment, no segments of the sealing member transmit a material part of the propulsive power to the propulsive means, a distinct structure moves within the hull that gives the stems of the propulsive means their motion, and the segments of the sealing member follow the motion of the stems of the propulsive means.

According to one embodiment, the solids that jointly cover the non-convex opening in the hull are connected to an inside structure that drives and controls the propulsive means.

According to one embodiment, the solids that jointly cover the non-convex opening in the hull are articulated and their following of the stems of the propulsive means is at least driven in part by the stems of the propulsive means as part of the hinge structure.

According to one embodiment, the solids that jointly cover the non-convex opening in the hull are organised in one layer. According to one embodiment, the solids that jointly cover the non-convex opening in the hull are organised in more than one layer, with one layer being placed in direct contact with the outside marine environment, and other layers being placed between the said layer and the inside of the ship hull. According to one embodiment, the solids that jointly cover the non-convex opening in the hull are organised in more than one layer, and the solids of the layer placed most outward can translate a little in the direction of the rotation axis of the propulsive means, in such a way that impact from immerged objects or wave slamming generates translation towards the hull; the solid then makes contact with a bearing on the hull and the large forces normal to the hull bypass the rest of the structure of the propulsor.

According to one embodiment the connection between the fin-stems and the segmented solids of the sealing body is flexible to allow bending of the fin- stems without causing substantial bending forces in the sealing body. According to one embodiment the connection between the fin-stems and the segmented solids of the sealing body is flexible to allow bending of the fin- stems without causing substantial bending forces in the sealing body.

According to one embodiment, the means for sealing is established at the periphery of the opening in the hull and at the rotating junction between the segmented solids in the sealing member.

According to one embodiment of the sealing body some segmented sealing solids are connected to the hull and/or to each other through a hydrostatic bearing system that bears forces with low friction and also allows for effective sealing of the perimeter. According to one embodiment, the means for sealing comprises conduits allowing a pressurised medium to access to the sealing surfaces. Brief description of the drawings

Fig 1 is a side view of a marine vessel equipped with a propulsive system to which the present invention relates

Fig 2 is a perspective view from aft and underneath the said marine vessel, showing an opening that the present invention seals, thereby separating the outside volume of the said vessel and the inside volume of the said vessel, and showing the endless path that the propulsive means follow with respect to the said opening.

Fig 3 has the same perspective view as Fig 2, but displays the invention as mounted, and also displays the propulsive means which are part of the propulsive system the invention relates to.

Fig 4 is a partial perspective view from the same angle as Fig 3 where various possibilities are shown with respect to if and where the stems of the propulsive means traverse the surface of relevant sealing solids Fig 5 is a partial bottom view of the said marine vessel showing an embodiment of the propulsive means and an embodiment of the complete sealing invention.

Fig 6 is a bottom aft perspective view an embodiment of the invention where the sealing solids do not transmit a material part of the propulsion forces to the propulsive means, and where the sealing solids follow the motion of part of separate actuating structure inside the hull.

Fig 7a and 7b are detailed partial views of 2 cross sections and 2 bottom views of an embodiment of the sealing invention for a propulsion system it relates to, showing enablement of the sealing function, means for sealing, and added functionality to prevent damage from slamming forces stemming from the outside environment. Detailed description of the invention with reference to the figures

Figure 1 is a side-view of a marine vessel (1 ) with a hull (2) containing a propulsion system with rotatable propulsive foils or fins (4) that move in an endless path, said endless path lying in a plane substantially parallel to an open- ing (3) through which the propulsive means (4) extend. The propulsion system could equally be placed in a large rudder without affecting the function and effectiveness of the invention presented in this document.

Figure 2 is a perspective view from aft and below of the hull (2) of the said marine vessel, and shows how the said opening (3) in the hull (2) is non- convex and surrounds an isolated part of the hull (2). The said endless path (9), that the said rotatable propulsive means (4) follow, is made visible in the opening (3) at the location of the projected hull surface.

Figure 3 is drawn from the same viewpoint as figure 2, and shows an embodiment of the inventive sealing member (5) as mounted in the hull (2), in- eluding sealing solids (6). Figure 3 also shows the propulsive means (4) extending into the water while mounted on rotatable stems (14). The face (8) of the sealing solids (6) facing away from the interior of the vessel are visible. The direction of flow is drawn for orientation purpose. The manner in which the sealing member (5), the sealing solids (6) and driving parts (14) and (13) jointly cover the said opening (3) is clearly visible; driving parts (13) of the said sealing solids (6) are visible but are further named in Figure 4 and Figure 5.

Figure 4 is a partial perspective view of an embodiment of the presented invention from aft below. It shows said sealing solids (6), the propulsive means (4) mounted on rotatable stems (14) and an embodiment of some driving elements (13), the movement of which determines the movement of the said sealing solids (6). In the definition of the driving elements (13) used in the whole text, the said fin-stems (14) may also be driving elements (13) of a sealing solid, and driving elements (13) may traverse and protrude from the said sealing solids (6) of the sealing member (5) so as to become apparent from underneath the ship. Figure 4 also shows various embodiments of the said sealing solids (6). In one embodiment of the sealing solid (6), a said driving element (13) or a said stem (14) of the propulsive means (4) is situated at a relative rotation point of two said sealing solids (6); in another embodiment this is not the case. In one shown embodiment of the sealing solid (6), said sealing solid (6) interfaces with a said stem (14) of a propulsive means (4); in another shown embodiment of sealing solid (6) this is not the case.

Figure 5 is a partial bottom view of an embodiment of the invention mounted in a hull (2) of the said vessel (1 ); it shows an embodiment of mountings (12) which allow sealing solids (6) to translate along the said endless path, and shows driving elements (13) that may include rotatable fin stems (14) on which propulsive means (4) are mounted. A cross- section of an embodiment of said mountings (12) is visible on figure 7a. Figure 6 is a partial perspective view from aft and below (same view as figure 3) of an embodiment of the invention where the sealing solids (6) do not submit substantial guiding forces, guiding moments and propulsion forces to the stems (14) of the propulsive means (4), but where a distinct articulated structure made of segments (15) in the form of an endless chain conveys the guiding and actuating forces to the said propulsive means (14). In this embodiment, the sealing segments (6) follow the path of driving elements (13) which in turn are driven by the said articulated structure.

Figure 7a and 7b are more detailed partial views of an embodiment of the presented sealing invention for endless path propulsion where, as in figure 6, the sealing solids (6) do not submit the actuation forces, actuation moments, guiding forces and guiding moments to the stems (14) of the propulsive means (4).

Figure 7a is a partial view of a side section of an embodiment of the presented sealing invention, a partial view of a length section of the same em- bodiment of the sealing invention, and a partial bottom view of the sealing solids (6) of the same embodiment of the sealing invention.

Figure 7a shows an embodiment where the sealing solids (6) are present in two distinct parallel layers. The top layer of sealing solids (6) may bear a large part of the static pressure forces from the outside water, and may submit the said static forces to sliding bearings (18) which in turn may submit most of said forces to earlier introduced mountings (12). In the absence of static pressure force facing inward the ship hull, weight forces of sealing solids (6) may be borne by sliding beating (19) to said mountings (12) of the sealing invention. A fluid under pressure may be injected between said sealing solids (6) and either said bearing (18) and/or said bearing (19) to alleviate friction forces and to improve reliability of the sealing invention. It is clear from the figure that is this embodiment moderate bending of the fin stems (14) due to elastic deformation under strain would cause moderate sideways translation of the sealing solids (6) in the bearings (18) and (19), which in turn would not affect the functionality of the sealing solution.

Figure 7a also shows how fin stems (14) may submit the driving force of the sealing elements to a journal bearing (20) that in turn may submit the driving force to the said sealing solids (6) to move along their said endless path. Fin stems (14) may be replaced by driving elements (13) arranged in a similar form compared to the sealing solids (6). The figure also shows how the journal bearing (20) may be double-sided, and may also interface with

neighbouring sealing solid (6) to help guide the said neighbouring sealing solid (6); a sliding/rotating connection may be utilised to allow bending of the stems (14) under strain without subjecting the solids (6) to material additional forces. Journal bearing (20) may also contain a rotating seal to improve the sealing function of the invention, and a fluid under pressure may be injected between said fin stem (14) and said journal bearing (20) to either enable the said rotating sealing function or to reduce friction, or both. A flexible connec- tion may be realised between said journal bearing (20) and said sealing solid (6) to allow moderate angular deflection of said stems (14) under strain without causing the said sealing solids (6) to exert materially increased forces to said bearing forces (18) and (19), and to increase reliability of the sealing invention. Figure 7a also shows how the lower layer of sealing solids (6) may absorb slamming forces caused by the external environment by compressing the elastic sliding connections (21 ) between the two layers of sealing solids (6) of this embodiment of the invention until the lower positioned sealing solid (6) comes in contact with the contingency bearing (17) placed on the said mountings (12) of the sealing invention. In this manner, said slamming forces may be transmitted directly to the mountings ( 2) of the sealing invention, and thereby directly to the hull (2), without subjecting large forces to the said sliding bearings (19) and (19), thereby increasing the reliability of operation of the system and also of the marine vessel as a whole. Sealing solids (6) may be equipped with compression chambers with a deforming surface that faces towards the volume between the parallel sealing solids (6) to reduce shock- waves stemming from said slamming.

Finally, figure 7a shows how sealing solids (6) may interface between each other with a grove connection to enable effective sealing at the rotation con- nection between the said sealing solids (6). This sealing function may be further improved by injecting a fluid under pressure at the location of the said grove.

Figure 7b is a bottom view of sealing solids (6) that shows an embodiment of the sealing invention according to figure 7a where the means for sealing are positioned at the full periphery of each said sealing solid (6). The hashed, dark, areas represent fully closed perimeters determined partially by the straight sections where a fluid may be injected between the said sealing solids (6) and the said linear bearings (18) and (19), and determined partially by the circular sections where a fluid may be injected between two adjoining sealing solids (6) in the grove connection. The fluid pressure in straight sections may be utilised to divert part of the said fluid to the circular sections through a cascaded feed as is common in stiffness compensated hydrostatic bearings.