A marine vessel

Abstract

The invention concerns a marine vessel (1) configured for roll-on loading and roll-off unloading of wheeled cargo (2), such as cars, trucks, buses and other vehicles, the marine vessel (1) comprising: a first cargo deck (3) arranged to carry wheeled cargo (2); a lower deck (4) located below the first cargo deck (3); first and second engines (11, 12) arranged on the lower deck (4), wherein the engines (11, 12) are arranged on opposite sides of a longitudinal centre line (20) of the marine vessel (1 ) and wherein each engine (11, 12) is operatively connected to a corresponding propeller shaft (13) for propulsion of the marine vessel (1); wherein an upper part (11a, 12a) of each engine (11, 12) extends through and above the first cargo deck (3), wherein each engine (11, 12) is provided with an exhaust pipe (11b, 12b) that extends from the upper part (11a, 12a) of the engine (11, 12) downwards through the first cargo deck (3) and then sideways below the first cargo deck (3) towards the longitudinal centre line (20) of the marine vessel (1) and further into a central casing (8) extending vertically upwards between the first and second engines (11, 12) towards a funnel (9) located above the first cargo deck (3) in an upper part of the marine vessel (1).

Description

This invention relates to a marine vessel configured for roll-on loading and roll-off unloading of wheeled cargo, such as cars, trucks, buses and other vehicles.BACKGROUND OF THE INVENTIONA marine vessel in the form of a roll-on / roll-off passenger ferry is commonly denoted a ROPAX vessel or ROPAX ferry. Such a vessel is adapted for rollon loading and roll-off unloading of wheeled cargo, such as cars, trucks, buses and other vehicles, and it typically comprises several cargo decks arranged on top of each other. One of these cargo decks forms a main entrance deck provided with an access ramp for wheeled cargo that preferably is vertically aligned, at least approximately, with quays to simplify loading and unloading. A ROPAX vessel also comprises compartments for passengers on some upper deck.There is a general need to reduce fuel consumption as well as environmental and climate impact of such vessels without too much negative impact on the cargo handling efficiency and capacity or on passenger areas.SUMMARY OF THE INVENTIONThe invention concerns a marine vessel configured for roll-on loading and roll-off unloading of wheeled cargo, such as cars, trucks buses and other vehicles, the marine vessel comprising: a first cargo deck arranged to carry wheeled cargo; a lower deck located below the first cargo deck; first and second engines arranged on the lower deck.The engines are arranged on opposite sides of a longitudinal centre line of the marine vessel and each engine is operatively connected to a corresponding propeller shaft for propulsion of the marine vessel. An upper part of each engine extends through and above the first cargo deck.Each engine is provided with an exhaust pipe that extends from the upper part of the engine downwards through the first cargo deck and then sideways below the first cargo deck towards the longitudinal centre line of the marine vessel and further into a central casing extending vertically upwards between the first and second engines towards a funnel located above the first cargo deck in an upper part of the marine vessel.The first cargo deck of this disclosure typically forms the main entrance deck of the ROPAX vessel.That an engine is operatively connected to a corresponding propeller shaft means it may be directly connected or indirectly connected via a gear arrangement or via an electric motor powered by the engine (via a generator and possibly also an electric battery).The marine vessel may comprise more than two engines, e.g. two engines may be connected to each of two propeller shafts, and the vessel may comprise e.g. three propeller shafts.The upper part of the engine that extends through and above the first cargo deck may include, for instance, a main cylinder cover, a turbocharger shaft and / or a piston top position.As explained further below, a special arrangement of the exhaust pipes is provided to allow for the above design of the marine vessel without too much negative impact on the cargo handling efficiency and capacity or on passenger areas,.A ROPAX vessel typically comprises at least two engines arranged side by side in engine rooms located on a double bottom tank top below the main entrance deck on opposite sides of the vessel longitudinal centre line, where each engine drives a corresponding propeller shaft and where a centre of a crank shaft is located some 3-3.5 m above the tank top bottom. The vertical distance between the tank top and the main entrance deck, i.e. the maximum height of the engine rooms, is typically limited to around 9-10 m due to the desired level of the main entrance deck (which should not only be approximately aligned with and reach the quays but also be located as low as reasonably possible for stability reasons) and the general design, draught etc. of marine vessels of ROPAX type and dimension. This vertical limitation has not been any particular issue in the past since conventional four-stroke engines used in marine vessels of typical ROPAX size have a height (above centre of crank shaft) that is relatively small, maybe around 4 m, and can thus be placed in this vertically limited space. There is even sufficient vertical room provided for certain maintenance work, such as lifting / removing pistons or cylinder linings. In turn this means, for instance, that there has neither been any particular issue how to arrange the exhaust pipes since even if the inlet end of the exhaust pipes are arranged at an upper part of the engines, the pipes can be allowed to extend in an upwards direction towards a vertically extending casing that may be located almost anywhere in the vessel (but preferably relatively close to the engines of course).However, there is a potential for reducing fuel consumption and climate impact of ROPAX vessels by using other types of engines that cannot be arranged in the vertically limited space between the tank top and the main entrance deck. In particular, two-stroke slow-speed engines have the potential of requiring a lower fuel consumption and, due to the lower engine speed (i.e. lower rpm), it is possible to dispense with any gear arrangement for the connection to the propeller shaft, which is necessary for four-stroke engines, so efficiency losses in the gear may be avoided. Further, two-stroke engines typically has a lower methane slip than four-stroke engines if running on liquid natural gas (LNG).A significant drawback of two-stroke engines for ROPAX application is, however, that they have a longer stroke and a substantially larger height than four-stroke engines of corresponding power. A suitable two-stroke engine may have a height of 7-8 m (above centre of crank shaft). This means that an upper part of such a two-stroke engine will extend through and above the main entrance deck / first cargo deck and thus occupy space on the main entrance deck intended as stowage space for the trucks, cars and other wheeled cargo. The upper engine part may also interfere with the movements of the wheeled cargo on the main entrance if the wheeled cargo is intended to move in a circular manner on that deck at loading or unloading. Because of the great height of suitable two-stroke engines, such engines have generally not been seen as a useful option for ROPAX vessels.Even if the disadvantages of having the upper parts of the engines extending through and above the main entrance deck are considered to be manageable, there is an additional complication related to such a design, namely how to route the exhaust pipes. Since the engines typically are arranged relatively close to the sides of the marine vessel, i.e. closer to the sides than to the longitudinal centreline of the vessel, a conceivable solution is to direct the exhaust pipe into and through side casings extending vertically along opposite sides of the vessel up to the funnel(s). However, in a ROPAX vessel provided with more than one cargo deck for wheeled cargo, there is a preference from a loading / unloading point of view that the cars / trailers are able to drive in a circular pattern on the cargo decks in order to, for instance, reach a tiltable ramp provided only on one side of the vessel for access up or down to other decks. In case side casings for exhaust pipes (and e.g. stairs and other piping) are provided, the width of the cargo decks is reduced and it will be more complicated and take more time to turn around e.g. a trailer in the parts of the deck where the side casings are located. In addition, side casings take up valuable outside areas on accommodation decks located above the cargo decks, i.e. it is not possible to arrange accommodation areas / cabins with windows where the side casing are located. This further explains why two-stroke engines, or other engines with significant height, objectively do not form a useful option for ROPAX vessels.The present disclosure concerns a marine vessel that allows for the use of engines, such as two-stroke engines, that are too high to be arranged below the first cargo deck / the main entrance deck without having to arrange side casings for the exhaust pipes. Instead each exhaust pipe is arranged to extend downwards through the first cargo deck, i.e. down into the vertically limited space between the double bottom tank top and the main entrance deck, and then sideways below the first cargo deck into a central casing extending vertically upwards between the first and second engines towards. The central casing is arranged in a longitudinally central positon of the vessel but need not be aligned with the longitudinal centreline of the vessel. Such a central casing does not affect a turning radius for vehicles at higher decks, and it is also better protected in case of a collision compared to side casings.Letting the exhaust pipe extend downwards and then upwards results in a U-shaped section of the exhaust pipe. Such sections are generally avoided since it may lead to accumulation of e.g. condensed water. A drain outlet may be arranged in the exhaust pipe at this section.In an embodiment, the marine vessel comprises at least a second cargo deck arranged to carry wheeled cargo, wherein the second cargo deck is located above the first cargo deck, and wherein the central casing extends vertically through both the first and the second cargo deck.In an embodiment, the marine vessel is provided with at least a first cargo access ramp in connection with the first cargo deck so as to allow wheeled cargo to roll-on and enter the marine vessel on the first cargo deck.In an embodiment, at least one of said engines is configured to operate according to a two-stroke cycle.In an embodiment, at least one of said engines is configured to operate with a nominal engine speed of less than 200 rpm.In an embodiment, a main cylinder cover of at least one of said engines is located above the first cargo deck.In an embodiment, at least one of said engines is provided with a turbocharging arrangement comprising a compressor arranged to be driven by an exhaust turbine via a turbocharger shaft, wherein a centreline of the turbocharger shaft is located above the first cargo deck.In an embodiment, the exhaust pipe extends at least 1 m in a downwards direction.In an embodiment, a drain outlet is arranged in the exhaust pipe at a section of the exhaust pipe that is located below the first cargo deck.In an embodiment, the first cargo deck is located above an operating waterline of the marine vessel.BRIEF DESCRIPTION OF DRAWINGSIn the description of the invention given below reference is made to the following figure, in which:Figure 1 shows a marine vessel according to the present disclosure.Figure 2 shows, in a transversal section of the vessel, an arrangement of engines and exhaust pipes according to a first embodiment.Figure 3 shows, in a top view of a first cargo deck, the arrangement according to figure 2.Figure 4 shows, in a longitudinal section of the vessel, the arrangement according to figure 2.Figure 5 shows, in a transversal section of the vessel, an arrangement of engines and exhaust pipes according to a second embodiment.Figure 6 shows, in a top view of a first cargo deck, the arrangement according to figure 5.Figure 7 shows, in a longitudinal section of the vessel, the arrangement according to figure 5.DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTIONFigure 1 shows a marine vessel 1 in the form of a ROPAX vessel provided with a plurality of cargo decks (see figures 2-7) and a plurality of accommodation decks. A cargo access ramp 7 is arranged in the aft of the vessel (i.e. to the left in figure 1). The marine vessel 1 configured for roll-on loading and roll-off unloading of wheeled cargo 2, such as cars, trucks buses and other vehicles. A funnel 9 is provided in an upper part of the vessel 1. Figure 1 also indicates an operating waterline 30 of the marine vessel 1.As shown in figures 2-7, the marine vessel 1 comprises first second and third cargo decks 3, 5, 6 arranged above each other and a lower deck 4 in the form of a double bottom tank top located as the next deck below the first cargo deck 3. The cargo access ramp 7 is arranged in connection with the first cargo deck 3 so as to allow wheeled cargo 2 to roll-on and enter the marine vessel 1 on the first cargo deck 3. The first cargo deck 3 forms a main entrance deck and is located above the waterline 30.First and second engines 11, 12 are arranged on the lower deck 4 on opposite sides of a longitudinal centre line 20 of the marine vessel 1. Each engine 11, 12 is operatively connected to a corresponding propeller shaft 13 for propulsion of the marine vessel 1 , see figures 4 and 7. (The vessel 1 is provided with two propeller shafts, one for each engine, but only one of the propeller shafts is shown in the figures.)As best shown in figures 2, 4, 5 and 7, an upper part 11a, 12a of each engine 11, 12 extends through and above the first cargo deck 3. Further, as best shown in figures 2 and 5, each engine 11, 12 is provided with an exhaust pipe 11b, 12b that extends from the upper part 11a, 12a of the engine 11, 12 downwards through the first cargo deck 3 and then sideways below the first cargo deck 3 towards the longitudinal centre line 20 of the marine vessel 1 and further into a central casing 8 extending vertically upwards between the first and second engines 11, 12 towards the funnel 9 located above the decks in the upper part of the marine vessel 1. The central casing 8 extends vertically upwards through all decks above the lower deck 4. Each exhaust pipe 11b, 12b extends at least 1 m in a downwards direction.As shown in figure 3, the central casing 8 comprises for fire safety reasons two separate exhaust compartments, one for each engine. The central casing 8 may extend significantly in the longitudinal direction of the vessel 1 and it may house e.g. stairs.A drain outlet 17a, 17b is arranged in each exhaust pipe 11b, 12b at a section of the exhaust pipe that is located below the first cargo deck 3, see figure 2. The drain outlet 17a, 17b allows for removing condensed water that may accumulate in this section of the exhaust pipe.In the embodiment of figures 2-4, each exhaust pipe 11b, 12b is arranged on a side of the corresponding engine 11, 12, i.e. the outlet of exhaust gas from the engine into the corresponding exhaust pipe is located on the side of the engine. In the embodiment of figures 5-7, each exhaust pipe 11b, 12b is arranged on an aft end of the corresponding engine 11, 12, i.e. the outlet of exhaust gas from the engine into the corresponding exhaust pipe is located on an aft end of the engine.Each engine 11 , 12 is in these examples configured to operate according to a two-stroke cycle and to operate with a nominal engine speed of less than 200 rpm. A main cylinder cover 11e, 12e of each engine 11, 12 is located above the first cargo deck 3, see e.g. figure 4. Each engine 11, 12 is provided with a turbocharging arrangement 11c, 12c comprising a compressor arranged to be driven by an exhaust turbine via a turbocharger shaft 11 d, 12d, and as shown in figure 5 a centreline of the turbocharger shaft 11 d, 12d may be located above the first cargo deck 3.The invention is not limited by the embodiments described above but can be modified in various ways within the scope of the claims.References in figures:1 - marine vessel2 - wheeled cargo3 - first cargo deck4 - lower deck (double bottom tank top)5 - second cargo deck6 - third cargo deck7 - cargo access ramp8 - central casing9 - funnel11, 12 - first and second enginesl la, 12a - upper part of enginesl lb, 12b - exhaust pipes11 c, 12c - turbocharging arrangement11 d, 12d - turbocharger shaft11 e, 12e - main cylinder cover13 - propeller shaft17a, 17b - drain outlet20 - longitudinal centre line of marine vessel30 - operating waterplane (max freeboard draught / deepest subdivision draught)

Claims

1. A marine vessel (1) designed for roll-on loading and roll-off unloading of wheeled cargo (2), such as cars, trucks, buses and other vehicles, the vessel (1) comprising:- a first cargo deck (3) arranged to transport wheeled cargo (2);- a lower deck (4) located below the first cargo deck (3);- first and second engines (11, 12) arranged on the lower deck (4),wherein the engines (11, 12) are arranged on opposite sides of a longitudinal centerline (20) of the vessel (1) andwherein each engine (11, 12) is operatively connected to a corresponding propeller shaft (13) for propulsion of the marine vessel (1); characterized in thatthat an upper portion (11a, 12a) of each engine (11, 12) extends through and above the first cargo deck (3),wherein each engine (11, 12) is provided with an exhaust pipe (11b, 12b) extending from the upper part (11a, 12a) of the engine (11, 12) downwardly through the first cargo deck (3) and then laterally below the first cargo deck (3) towards the longitudinal centre line (20) of the marine vessel (1) and further into a central casing (8) extending vertically upwards between the first and second engines (11, 12) towards a chimney (9) which is positioned above the first cargo deck (3) in an upper part of the marine vessel (1).

2. The marine vessel (1) according to claim 1, wherein the marine vessel (1) comprises at least one second cargo deck (5) arranged to transport wheeled cargo (2), wherein the second cargo deck (5) is positioned above the first cargo deck (3) and wherein the central casing (8) extends vertically through both the first and second cargo decks (3, 5).

3. The marine vessel (1) according to claim 1 or 2, wherein the marine vessel (1) is provided with at least one first loading ramp (7) adjacent to the first cargo deck (3) to allow wheeled cargo (2) to roll onto and enter the marine vessel (1) on the first cargo deck (3).

4. The marine vessel (1) according to any one of the preceding claims, wherein at least one of said engines (11, 12) is configured to operate according to a two-stroke cycle.

5. The marine vessel (1) according to any one of the preceding claims, wherein at least one of said engines (11, 12) is configured to operate at a nominal engine speed of less than 200 revolutions per minute.

6. The marine vessel (1) according to any one of the preceding claims, wherein a master cylinder housing (11e, 12e) for at least one of said engines (11, 12) is positioned above the first cargo deck (3).

7. The marine vessel (1) according to any one of the preceding claims, wherein at least one of said engines (11, 12) is provided with a turbocharging device (11c, 12c) comprising a compressor arranged to be driven by an exhaust turbine via a turbocharging shaft (11d, 12d), wherein a centerline of the turbocharging shaft is located above the first cargo deck. (3).

8. The marine vessel (3) according to any one of the preceding claims, wherein the exhaust pipe (11b, 12b) extends at least 1 m downward.

9. The marine vessel (1) according to any one of the preceding claims, wherein a drain outlet (17a, 17b) is arranged in the exhaust pipe (11b, 12b) at a section of the exhaust pipe located below the first cargo deck (3).

10. The marine vessel (1) according to any one of the preceding claims, wherein the first cargo deck (3) is located above an operating waterline (30) of the vessel (1).