MARINE VESSEL

The present invention relates to a marine vessel with at least a first cargo facility at a stern end of the marine vessel and at least a second cargo facility at a bow end of the marine vessel, in which marine vessel a deckhouse is arranged between the first cargo facility and the second cargo facility, and which marine vessel comprises a first propulsion unit and a second propulsion unit which form a CRP propulsion system, according to the preamble of claim 1.

In the following the terms "aft", "rearward", "front", "forward" and similar expressions are to be understood in the context of the stern of the marine vessel being considered the rear of the marine vessel and the bow of the marine vessel being the front of the marine vessel.

In cargo carrying marine vessels the cargo carrying capacity is of course of great importance. Operating costs, particularly for power generation, constitute another important factor. Modern high-speed cargo vessels require a high amount of propulsion power, but propeller blade loads may become critical especially when using a single screw. Generally a single screw with a largest possible diameter is desir- able when seeking high propulsion efficiency. The draught of a ship may however become a limiting factor.

An object of the present invention is to avoid the drawbacks of known solutions and to provide a cargo carrying marine vessel which maximises the cargo carrying ca- pacity and provides an efficient and redundant way to utilize power in the marine vessel. This object is attained by a marine vessel according to claim 1.

The basic idea of the invention is to use a propulsion system with enhanced hydro- dynamic characteristics compared to a single screw while maintaining a cargo car- rying capacity which remains more or less the same as with a single screw machinery arrangement. This is realized by means of a first propulsion unit and a second propulsion unit forming a CRP (Contra Rotating Propeller) propulsion system,

and by arranging the machinery for both propulsion units on top of each other in the same compact space below the deckhouse of the marine vessel.

The CRP propulsion system is efficient and fuel saving in view of conventional sys- terns and provides more power because power is divided between the contra rotating propellers of the CRP propulsion system. When using a CRP propulsion system the most efficient hull form, comprising a single skeg, may be used. Furthermore, the CRP propulsion system provides redundancy.

By arranging the machinery of both propulsion units, i.e. comprising the first power unit of the first propulsion unit and the second power unit of the second propulsion unit, on top of each other below the deckhouse, more space allocation for the cargo is achieved. Thus the machinery is arranged in the same compact space, whereby ducting, cabling and installation of auxiliary equipment are made cost- efficient and simple. In addition, stores, workshops and other technical spaces may also be arranged within such a column formed sphere below the deckhouse optimizing the use of space on the vessel. Accommodation space may also be confined to the deckhouse area.

Preferably the first power unit, located in a first engine room, the second power unit, located in a second engine room, and the deckhouse are located on top of each other on respective decks of the marine vessel.

The first propulsion unit of the CRP propulsion system comprises the first power unit, a first drive train and a first propeller unit. The first propeller unit constitutes the front propeller of the CRP propulsion system. The second propulsion unit of the CRP propulsion system comprises the second power unit, a second drive train and a second propeller unit. The second propeller unit constitutes the aft propeller of the CRP propulsion system.

The first propulsion unit advantageously comprises a conventional mechanical propulsion arrangement, whereby the first power unit may be an internal combus-

tion engine, gas turbine, etc., and the first drive train may comprise a horizontal drive shaft connecting to the front first propeller unit. The second propulsion unit advantageously comprises a mechanical steerable thruster with the second drive train comprising a so-called z-drive unit connecting to the aft second propeller unit.

In this case it is advantageous to arrange the second power unit below the deckhouse, over the first power unit.

The benefits of the present invention are highly noticeable in connection with a container ship. The compact space arrangement of the deckhouse on top of the engine rooms located vertically below gives a high container loading capacity tak- ing into account the standardized measures of containers. The IMO (International Maritime Organisation) rules of sight may also be fulfilled with said high container loading capacity.

Consequently, this means that CRP propulsion can be used without sacrificing cargo capacity.

In the following the present invention is described in more detail, by way of example only, with reference to the attached schematic drawing which shows an advantageous embodiment of the present invention.

The drawing shows a marine vessel 1 , in this embodiment a container ship. The marine vessel 1 has a stern end indicated by reference numeral 2 and a bow end indicated by reference numeral 3. The marine vessel 1 is provided with at least a first cargo facility 4 at the stern end 2 and at least a second cargo facility 5 at the bow end 3 of the marine vessel. The first cargo facility 4 is shown to include at least one aft cargo hold 41 , in this case three aft cargo holds for receiving contain- ers 10. The second cargo facility 5 only shows one front cargo hold 51 for receiving containers 10. It is clear that more cargo holds may be provided at the bow end 3 of the marine vessel 1. A deckhouse 6 is arranged between the first cargo facility 4 and the second cargo facility 5, in this embodiment between the most forward aft cargo hold 41 and the most rearward front cargo hold 51. The marine vessel is also provided with a propulsion system.

The propulsion system includes a first propulsion unit 8 including machinery comprising a first power unit 81 and a second propulsion unit 9 including machinery comprising a a second power unit 91 , which propulsion units form a CRP (Contra Rotating Propeller) propulsion system 7. CRP propulsion systems are known per se, i.e. known to a person skilled in the art, and are therefore not described in more detail in this connection.

The first propulsion unit 8 comprises a conventional mechanical propulsion unit with a first power unit 81 , e.g. an internal combustion engine, a gas turbine, etc., which rotates a front first propeller unit 84 by means of a first drive train 82 comprising a generally horizontally arranged main shaft 83. The second propulsion unit 9 comprises a mechanical steerable thruster, with a second power unit 91 , which rotates a second propeller unit 98 by means of a second drive train 92 (forming a z-drive) comprising a generally horizontally arranged first drive shaft 93, a first angle transmission 94, a generally vertically arranged second drive shaft 95, a second angle transmission 96, and a generally horizontally arranged propeller shaft 97 connecting to the second propeller unit 98. Basically in this CRP propulsion system 7 the first propeller unit 84 and the second propeller unit 98 are positioned rela- tively near to each other, whereby the main shaft 83 rotating the first propeller unit 84 and the propeller shaft 97 rotating the second propeller unit 98 are parallel and in alignment with each other. The main shaft 83 connecting to the first propeller unit 84 and the first drive shaft 93 of the second propulsion unit 9 may also be arranged basically in parallel on separate decks towards the stern end 2 of the ma- rine vessel 1.

In the following we shall discuss the machinery and space arrangement for the first propulsion unit 8 and the second propulsion unit 9.

In a marine vessel 1 like a container ship the deckhouse 6 usually is located in the stern end quarter of the ship with respect to its length. In the drawing the deckhouse 6, preferably including accommodation space, etc., extends above the

loaded containers 10 providing the bridge with sight according to prevailing rules as discussed above. A second engine room 99, where the second power unit 91 driving the mechanical steerable thruster is located, is situated below the deckhouse 6, over a first engine room 85, where the first power unit 81 driving the con- ventional mechanical propulsion unit is located. In such an arrangement, the deckhouse 6, the second engine room 99 and the first engine room 85 practically form a generally vertical column or column formed sphere forming the ships operational area between the cargo holds, which does not obstruct or limit the cargo facilities of the marine vessel 1.

Furthermore, cabling, ducting and arrangements for auxiliary equipment may be carried out and designed in a cost-effective and simple manner in this compact operational area. Stores, workshops and other technical spaces can thus also be rationally located within this area with direct access to the pertinent equipment. This in connection with the CRP propulsion system provides a most efficient transport concept.

The drawing and the description related thereto are only intended for clarification of the basic idea of the invention. The invention may vary in detail within the scope of the ensuing claims.