RISER SYSTEM This invention relates to a riser system and in particular to an assembly for and a method of installation and recovery of a seawater intake riser on a Floating Production Storage and Off-loading (FPSO) vessel or similar.

Seawater intake risers are generally installed in FPSO's to provide a means of obtaining low oxygenated water for the FPSO cooling, process, utility and/or water injection systems. Seawater intake risers are typically attached to seawater intake grids located below water level on the port and/or starboard sides of a FPSO hull or similar converted tanker.

Known seawater intake riser systems must generally be installed on an FPSO by divers and/or ROV's.

However, the use of divers and ROV's can increase costs and the time required to install seawater intake riser systems on FPSO's.

An object of the invention is to overcome the problems of the prior art.

According to the invention there is provided a vessel riser system assembly comprising mounting means for receiving a riser, attachment means for attaching the riser to the mounting means, sealing means for forming a sealing relationship between the attachment means and the mounting means and remotely operable locating means for automatically locating the attachment means on the mounting means at sea.

Preferably, the mounting means comprises a sea chest. More preferably, the sea chest comprises a sea chest flange for receiving the attachment means.

Most preferably, the attachment means comprises a sea chest connection flange attachable to the riser.

Advantageously, the sealing means is located between the sea chest flange and the sea chest connection flange. Preferably, the sealing means comprises pressure activated sealing means. Suitably, the sealing means comprises suction activated sealing means.

In a preferred embodiment of the invention, the locating means comprise guide means. Preferably, the guide means comprise a track mountable on the vessel. Preferably, the guide means comprise positioning means for positioning the sea chest connection flange at the sea chest flange.

The invention also extends to a method of installing a seawater intake riser on a vessel comprising feeding a riser to a seawater intake grid on a vessel hull by sliding the riser along a guide means located on the hull of the vessel. Preferably, the guide comprises a track between the seawater intake grid and a location above sea level.

Advantageously, a sea chest connection flange is slid in the track and located at a sea chest flange at the seawater intake grid.

Preferably, the method further comprises forming a seal between the sliding flange and sea chest located at the seawater intake grid.

Most preferably, the seal is formed by pressure actuation.

The invention therefore extends to an assembly and method of installing a seawater intake riser on a FPSO by attaching the seawater intake riser to sea water intake grids located below water level on the port and/or starboard side of a FPSO hull or similar converted tanker.

The assembly and method of the invention therefore provides a means for installation and hook-up of the intake risers at sea to be a"diverless"off-shore operation.

Various embodiments of the invention will now be described, a way of example only, having regard to the accompanying drawings in which: Figure 1 is a partially cut away side elevation of a FPSO fitted with an assembly in accordance with the invention; Figure 2 is a front elevation of the FPSO of Figure 1 with an assembly of the invention located on the port and starboard sides of the FPSO; Figure 3 is an enlarged view of the assembly of the invention mounted on the FPSO; Figure 4 is enlarged view of the sea chest connection flange and sea chest flange of the assembly of the invention; Figures 5a to 5f show the sequential method of installing a seawater intake riser to the FPSO in accordance with the invention.

As shown in the drawings an FPSO to be fitted with a riser 7 is generally indicated by the reference numeral 1. The FPSO is provided with a crane 2 for locating the riser 7 as shall be explained more fully below. Typically, the FPSO has a maximum draft, A, of 21 metres indicated by a broken line 3 and a minimum draft, B, of 8 metres indicated by a broken line 4.

In Figure 1, the FPSO is partially cut away so that the aft 6 of the FPSO only is shown.

An assembly of the invention is generally indicated by the reference numeral 5 and is located on the port 10 and starboard 11 sides of the FPSO 1. The assembly 5 is made up generally of a sea chest component 8, a track 9 in communication with the sea chest 8 and the riser 7 attachable to the sea chest 8.

The sea chest 8 is typically pre-fabricated and attached to the FPSO 1 in dry dock prior to off- shore operations. In particular, the sea chest 8 is attached to the hull 12 of the FPSO 1 at a seawater intake grid 18. The sea chest 8 is mounted or welded to the hull 12 and is provided with a robust sea chest flange 14.

The track 9 is made up of parallel first and second rails 15,16 respectively which extend upwards from the sea chest 8, either side of the sea chest 8, at the sea water intake grid 18. The track 9 is attached to the side of the FPSO between the FPSO deck top side and the seawater intake grid 18. The track 9 like the sea chest 8, is attached to the hull 12 of the FPSO in dry dock prior to off-shore operations.

The riser 7 is of substantially conventional construction with the exception that the riser 7 is provided with a sea chest connection flange 13 for

forming a mating relationship with the sea chest flange 14. The sea chest connection flange 13 is provided with a robust pressure/suction energised seal for mating to the sea chest flange 14. The sea chest connection flange 13 is also provided with a riser connection 19 for receiving the riser 7. The sea chest connection flange 13 can be further provided with an optional seal connection to accommodate a hypochloride injection line (within the riser 7) adapted to receive hypochloride to destroy marine algae and the like which can invade the riser 7.

The riser 7 is connected to the sea chest connection flange 13 at the riser connection 19. Typically, the riser 7 is built up of short lengths of flexible hosing or rigid piping interconnected via bolted flange connections. The short lengths of the riser 7 facilitates ease of handling during transportation.

A lowering wire 17 is disposable between the sea chest connection flange 13 and the crane 2 to facilitate raising and lowering of the sea chest connection flange 13 in the track 9. Accordingly, the lowering wire 17 enables the sea chest connection flange 13 (and the riser 7 attached to the sea chest connection flange 13) to be lowered or recovered and to be located above FPSO deck/sea level as required.

In use, the assembly 5 of the invention is normally mounted on the port 10 and/or starboard 11 side of the FPSO 1. As indicated above, each assembly is generally, made up of a sea chest connection flange 13 coupled to a flexible intake riser 7 and a fabricated track or guide assembly 9 mounted to the hull 12 of the FPSO, the sea chest connection flange 13 being sealably attachable to the sea chest flange 14 on the sea chest 8.

As shown in Figure 5, in order to locate the riser 7 at the sea water intake grid 18, the sea chest connection flange 13 and the riser 7 are simply fed into the track 9 above sea level employing the lowering wire 17 from the crane 2. The sea chest connection flange and riser located in the track 9 is then simply lowered and guided down the track 9 to below sea level to locate at a connection position with the sea water intake grid 18 located at the sea chest flange 14. The first and second rails 15,16 of the track 9 are provided with stop/locating means to locate the sea chest connection flange 13 adjacent the sea chest flange 14 of the sea chest 8 to facilitate sealing of the sea chest connection flange 13 with the sea chest flange 14. The sea chest connection flange 13 is then secured to the sea chest flange 14 by an automatically activated clamp system.

Accordingly, the sea chest connection flange 13 is mated against the sea chest flange 14 in a sliding action resulting from sliding the sea chest

connection flange 13 along the rails 15,16 of the track 9.

Moreover, as indicated above, the sea chest connection flange 14 is provided with a suction energised seal indicated by the reference numeral 20 which is activated due to a pressure differential created when sea water is pumped into the riser 7.

The pressure differential created results in a sealing effect familiar to those skilled in the art.

Such seals are available under the Trade Name Eddelbuttel and Schneidr and are conventionally used in the dredging art.

Sliding of the sea chest connection flange 13 against the sea chest flange 14 ensures that the flanges are not damaged during mating and seal integrity is not compromised. Moreover, the sea chest connection flange 13/sea chest flange 14 clamp system can be operated remotely from the FPSO deck or from within the hull 12 without the need for divers or ROV operations.

The advantages of the invention are many. A sea chest connection flange 13 and the water riser 7 can be accurately lowered to the correct connection location in relation to the seawater intake grids 18 on an FPSO via the track 9 in a simple single lowering operation. The sea chest connection flange 13 is automatically positioned in the track 9 to effect a sealing relationship with the sea chest flange 14 without the need for further sealing connection alignment. The sea chest connection

flange 13 is fitted with a suction energised seal and the hypochloride injection flange connection is fitted with a similar pressure energised seal while the flanges 13,14 can be mated together in a sliding action which does not result in damage or does not interfere with seal integrity.

Finally, the assembly of the invention can be operated remotely from the vessel deck or from within the vessel hull without requiring divers or ROV operations.