GB2071580A - Service vessels for offshore work - Google Patents

Abstract

A multi-purpose service/emergency vessel has a basic hull construction which is ideally suited for building in a variety of different sizes and configurations, enabling vessels of different draught and function to be built to a more or less standard design. Thue the vessel has hull sections at the waterline with vertical outer walls, including stem (15) and stern, so that vessels of different draught can be built by incorporating waterline hull sections of different depths. All propulsion machinery can be lifted out through a container hold aft of the engine room. To facilitate external welding repairs at sea the outboard lateral tanks are filled with water and ballast, the fuel tanks being inboard of these lateral tanks. <IMAGE>

Description

SPECIFICATION Service/emergency vessel This invention relates to a service/emergency vessel, and particularly a multi-purpose vessel capable of being used as a tug, for supply and maintenance, for anchor handling, fire fighting, and as a diver support vessel.

The vessel of the present invention is designed to have particular, but not exclusive, utility as a service/emergency vessel for offshore rigs. The object of the invention is to provide a vessel with a unitary design, capable of being built with a wide range of draughts and propulsion equipment, for employment in different roles as a tug, support vessel, emergency vessel, or the like, thereby avoiding the need for numerous vessels of radically different design, which are at present built almost exclusively by specialist ship-builders.

The present invention provides a service/emergency vessel having a hull section at the waterline which is fabricated with vertical outer walls, including both the stem and stern portions of the vessel, so that vessels of different draught can be built by incorporating waterline hull sections of different depth.

The vessel preferably has holds capable of receiving cargo-containers, fuel tanks outboard of the holds, and water tanks outboard of the fuel tanks. Water may be carried in the outboard tanks, either as ballast, or as cargo for delivery to an offshore rig, for example as fresh water or drill cooling water.

By locating the water tanks outboard of the fuel tanks the risk of fire in the event of a collision is minimised. Furthermore, the down time required to effect welding repairs on the hull of the vessel is greatly reduced, since it is not necessary to carry out the tank degassing safety procedures which are an essential preliminary to welding work on hulls with outboard fuel tanks. The holds of the vessel are preferably designed to carry standard containers for any desired type of cargo, such as bulk liquid, liquefied gas, bulk solids or other goods, Without any structural modification of the holds.

The vessel is preferably provided with propulsion screws, each driven by a group of engines through gearing, the engines being removable individually through deck hatches. The changing of individual engines is thereby facilitated, and does not necessitate a major refitting operation or structural modification. This again reduces down time of the vessel during refit or repairs, since work on the engines does not have to be carried out in the confined space of an engine-room.

The construction of the vessel with a waterline hull section having vertical outer walls facilitates the building of the vessel with a shallow or deep draught, according to its intended role. For example, where the vessel is intended to be used as a tug it would be designed with a deep draught, so as to accommodate propulsion screws of large diameter. but the basic design of the vessel would not undergo radical change, since the draught would be achieved by the incorporation of a waterline hull section of the appropriate depth.

The propulsion screws of the vessel are preferably housed, as known per se, in swivellable or fixed nozzles (Kort nozzles). Where fixed nozzles are employed each is preferably associated with twin rudders on opposite sides of the propeller shaft, thereby facilitating shaft inspection when the vessel is in dry-dock.

The vessel may be provided with a bow and/or stern water thruster units arranged for 3600 directional thrust or transverse thrust, to give improved position-keeping. These thruster units are preferably removable for repair while the vessel is in the water.

A hoisting gantry may be mounted for movement longitudinally on guides along opposite sides of at least one of the holds for loading and unloading the latter. The gantry is preferably such that the vessel can be loaded and unloaded without the assistance of quay-side cranes or hoists. In addition to serving the or each hold, the hoisting gantry may be movable into an after position in which it can be used for hoisting diving gear for underwater maintenance, for example on an offshore rig.

The invention is illustrated, by way of example, in the accompanying drawings, in which: Figure 1 is a diagrammatic side elevational view of a vessel according to one embodiment of the invention; Figure 2 is a partial plan view, partly in section, of the vessel illustrated in Figure 1, showing the arrangement of the propulsion screws and their associated engines; Figure 3 is a diagrammatic side elevation, corresponding to Figure 1 , showing a vessel according to a second embodiment of the invention, of deeper draught, designed for heavy towing work and as a diver support vessel; Figure 4 is a plan view of the vessel shown in Figure 3, at the tanktop level, and showing in broken outline the positions of the propulsion screws and the propulsion unit associated with one of these screws;; Figure 5 is a stem elevational view of the vessel show in Figures 3 and 4; and Figure 6 is a plan view at main deck level of the vessel shown in Figures 3, 4 and 5.

The vessel illustrated in Figures 1 and 2 is a relatively shallow draft service/emergency vessel in accordance with the invention, designed as a fire-fighting and general purpose tender for servicing offshore rigs. The vessel has cargo carrying holds 1 accessible through deck hatches, the holds being of such dimensions that they can accommodate standard twenty foot containers for goods, bulk cargo or bulk liquid.

Outboard of the holds 1 the hull is provided with tanks 2 for bulk liquid and/or fuel. Preferably, the hull is equipped with freshwater tanks 3 outboard of cargo and fuel tanks.

The vessel is equipped for deep-sea towing and has two independent towing winches (not shown), and towing bollards 4 arranged symmetrically on the port and starboard sides of the main deck, approximately amidships, preferably close to or slightly aft of the centre of buoyancy of the vessel.

Aft of the towing bollards 4 the main deck of the vessel is provided with hawser guides 5 for guiding a towing hawser when the vessel is used as a tug. The hawser guides 5 act as a pivot point for a towing line under tension; this pivot point is ideally positioned about one third of the length of the vessel from the stern.

The vessel is equipped for fire-fighting, and for this purpose has high capacity pumps for pumping sea water through angularly adjustable nozzles 6 carried on a foremast 7 and mainmast structure 8.

The propulsion of the vessel illustrated in Figures 1 and 2 is provided by triple screws 9 (Figure 2), the outboard screws 9 being surrounded by swivellable nozzles 10 having associated rudder vanes 11. Each of the screws 9 is driven by a pair of 990 bhp diesel engines 12 coupled to the associated propeller shaft 13 through a respective gearbox 14.

The vessel has a waterline hull section 1 5 which is fabricated with vertical outer walls, including both the stem and stern portions of the vessel. The waterline section 15 and the double bottom of the vessel are constructed with vertical longitudinal and transverse bulkheads. This facilitates the construction of vessels with hulls of different draught, to meet a user's specific requirements, without radically changing the overall design concept. Thus the vessel illustrated in Figures 1 and 2 may be constructed, with the same overall layout, but with waterline hull sections 1 5 of different depth, according to the propulsive power required.The vessel can, moreover, be fabricated with different overall lengths, and the length of any one vessel can be modified in dry-dock, by the addition of predesigned transverse hull sections of appropriate length.

The internal bulkheads are constructed where practicable from flat swedged or corrugated plating for strength combined with lightness.

In the example of Figures 1 and 2 the vessel has a draught of 480 cm and triple propulsion screws developing a total power of 5940 bhp. In a variant of the design, the vessel may be equipped with twin propulsion screws of larger diameter developing 6200 bhp, with a draught of 600 cm.

In a third, heavy duty, variant of the invention, illustrated in Figures 3 to 6, the hull is designed with a draught of 720 cm and has twin propulsion screws 9 developing a total power of 24000 bhp.

The twin screws 9 are both housed in swivellable Kort nozzles 10 and associated rudder vanes 11, the two screws being separated by a fixed longitudinal keel skeg. Alternatively, the vessel may have a fixed Kort nozzle surrounding each propulsion screw 9, each nozzle having a pair of rudders disposed symmetrically on opposite sides of the propeller shaft axis, to facilitate shaft inspection and repair.

To improve the water flow to the propulsion screws 9 the hull bottom is preferably formed with longitudinally extending arcuate tunnels 16 aligned with the respective screws.

In the heavy duty vessel of Figures 3 to 6 each propulsion screw 9 is driven by three 4000 bhp diesel engines 12 coupled to the associated propeller shaft 13 through a respective gear transmission 14. Each diesel engine 12 and associated machinery is independently removable for servicing and replacement through a container hold aft of the engine room, which is accessible through a forward container-sized cargo hatch 1 7 (Figure 6). Such removal through the hatch 1 7 can be effected using the vessel's own hoisting gear, described later.

The vessel of Figures 3 to 6 is equipped for the servicing of oil rigs and has tanks 2a, outboard of the propeller shaft 13, for drill water, in addition to separate outboard tanks 3 for fresh water. Fuel, either as cargo or for the vessel's consumption, is carried in tanks 2b inboard of the propeller screws 13. Detergent or foam is carried in tanks 2c inboard of the fresh water tanks 3.

The vessel of Figures 3 to 6 is equipped for cargo handling without the assistance of quayside facilities. For this purpose the vessel is fitted with a gantry 1 8 which moves on longitudinal rails 19 along opposite sides of the after deck of the vessel. The gantry 18 is equipped with hoisting gear for servicing the cargo holds of the vessel. In addition, when the gantry is moved into its fully aft position it can be used for hoisting diving gear, for underwater maintenance, over the stern of the vessel. Instead of the gantry 1 8 a 30 ton s.w.l.

derrick crane may be provided.

The vessel illustrated in Figures 3 to 6 is readily adaptable for use as a diver support vessel and for this purpose it is equipped, at an approximately midships position, with a downwardly open well or "moon pool" 20 affording direct and sheltered access to the sea for divers and diving equipment.

For vessels whose specification does not call for a moon pool the well would be closed by a bottom wall and would be used as a chain locker or a fuel tank.

The multi-purpose vessel illustrated and described in the drawings can be used in a number of different operational roles, including use as a deep sea tug and salvage vessel, and use as a tender for carrying supplies to and from offshore rigs. All the special equipment necessary to adapt the vessel to different roles is ideally in modular form so that it can be installed and removed without structural modification of the vessel. For example, the towing winches and bollards, and container handling gantry can be fitted and anchored in position by bolts, the hull construction being designed with the required strength to receive such equipment. The positions of the towing winches, bollards, and of storage reels for towing cables, can be selected to suit the user's requirements.

Separate anchor handling winches may be provided. The vessel may have a whaling stern incorporating a roller bed 20 (Figures 3 and 6) to facilitate heavy lifts during anchor handling operations. Access to the whaling stern section 20 is closed, when not in use, by hinged stern gates 2 1.

The trim of the vessel can be easily and quickly adjusted to suit different operational roles by the transfer of liquid cargo, fuel, or water, between forward and aft tanks. This avoids the extensive use of ballast for trimming, which is not costeffective.

It will be noted from Figures 1 and 3 that the keel of the vessel has a maximum depth, possibly equipped with the water flow tunnels 1 6, extending from an aft position substantially one third of the vessel's length from the stern, to a forward position about 1/4-1/5th of the vessel's length from the stern. The length of the keel part of maximum depth is, as a result, shorter than this length on most comparable vessels, a feature which assists the pivoting of the vessel about a vertical axis; the pivot axis would typically be about 2/3rd of the vessel's length from the stern.

This in turn improves the manoeuverability of the vessel.

The manoeuverability of the vessel is further increased by the provision of bow and stern thruster units. In the vessel illustrated in Figure 3 these thrusters take the form of vertically mounted thruster units 22 in the hull bottom. Each thruster unit directs thrust through a rotatable outlet nozzle equipped with flow deflecting vanes, so that the thrust can be directed selectively through 3600 about a vertical axis by controlled rotation of the nozzle. Two such thruster units 22 may be mounted in the bow section and two in the stern section of the vessel.

In addition to the vessel's versatile cargocarrying capacity afforded by the containerised holds, the vessel also has clear after deck space for a variety of deck cargo. An important cargo frequently carried by oil rig servicing vessels is long sections of pipe: such pipe sections can be carried athwartships of the deck to improve the drainage of water from the pipes when the vessel is in a heavy sea.

Claims (10)

1. A service/emergency vessel having a hull section at the waterline which is fabricated with vertical outer walls, including both the stem and stern portions of the vessel, so that vessels of different draught can be built by incorporating waterline hull sections of different depth.

2. A service/emergency vessel as claimed in Claim 1, having holds capable of receiving cargocontainers, fuel tanks outboard of the holds, and water tanks outboard of the fuel tanks.

3. A vessel according to Claim 1 or Claim 2, in which the vessel has screws, each driven by a group of engines through gearing, the engines being removable individually through deck hatches.

4. A vessel according to any one of the preceding claims, in which a hoisting gantry is supported for movement longitudinally on guides along opposite sides of at least one of the holds for loading and unloading the latter.

5. A vessel according to Claim 4, in which the hoisting gantry is movable into an after position in which it can be used for hoisting loads over the stern of the vessel.

6. A vessel according to any one of the preceding claims in which the propulsion screws of the vessel are housed in swivellable or fixed nozzles.

7. A vessel according to Claim 6, in which the propulsion screws are housed in fixed nozzles and twin rudders are mounted downstream of each nozzle, on opposite sides of the associated propeller shaft.

8. A vessel according to any one of the preceding claims in which bow and/or stern thruster units are provided, each being capable of directing thrust transversely, and each being removable for repair or replacement when the vessel is in the water.

9. A vessel according to Claim 8, in which the or each thruster unit is swivellable through 3600.

10. A vessel according to any one of the preceding claims, in which the hull bottom is provided with longitudinally extending water flow tunnels extending forwardly from each propulsion screw to improve water flow to the screw.

1 1. A service/emergency vessel substantially as herein described with reference to and as shown in Figures 1 and 2 or Figures 3 to 6 of the accompanying drawings.