Preparation and expertise

The closing weeks of last year saw the completion of two demanding ocean towage and heavy transportation assignments by Rotterdam-based Fairmount Marine. The company completed its project management contract for the delivery of Shell?s Bonga ? the world?s largest FPSO ? from the UK to Nigeria. Two weeks later, a Fairmount-managed tug delivered the 14,000 tonnes Murphy Oil Frontrunner SPAR at Pascagoula, USA, following a 9,700 nautical mile voyage from the build yard at Jebel Ali, UAE.

On November 27, Fairmount?s Senior Towmaster Captain, Klaas Bakker, on the bridge of lead tug Far Saltire (Farstad Shipping), gave instructions to disconnect from the 300,000 dwt Bonga. They had reached the handover position in Nigerian waters after a voyage of 4,770 nautical miles ? Far Saltire, Smitwijs Rotterdam and Wolraad Woltemade ?completed the 36-day voyage from the UK at an average speed of 6 knots.

Shell?s FPSO was built by Samsung, Korea, and outfitted at AMEC?s Wallsend yard. Bonga represents an investment of $770 million and is the highest value tow so far performed by Fairmount. It will operate off the Niger Delta, in a water depth of 1,000 m and has storage for two million barrels. Oil will be exported by tankers and gas will be pumped to the Bonny LNG plant.

The Bonga towage contract was awarded to Fairmount by Single Buoy Moorings (SBM). A joint technical group was established to manage the towage task. BITT (Bonga Integrated Towing Team) involved Shell, AMEC, SBM, Noble Denton and Fairmount.

Fairmount brought considerable FPSO/FSO towage expertise to this group?s meetings. The company?s 2003 programme also included an 11,308 nautical mile tow from Ulsan, Korea, to offshore Nigeria involving the FSO Unity. Two of the large Chinese tugs in Fairmount?s managed fleet, De Hong and De Xiang (185 tonnes and 153 tonnes bollard pull respectively), completed this voyage on April 21 2003. The average tow speed was 5.2 knots. Last year?s activities also included the positioning of the FPSO Serpentina (offshore Equatorial Guinea) and the tow of the FSO Domy-XV (Nigeria to offshore Pointe Noir).

The Unity ocean tow contract was also awarded by SBM. This assignment set the pattern for the subsequent Bonga voyage, with an extensive programme of preparatory work. A joint team involving Fairmount, SBM, Elf Petroleum Nigeria, builders Hyundai and warranty surveyors London Offshore Consultants ensured the FSO?s safe delivery.

Safety induction

The FPSO Bonga has a length (O/A) of 305.1 m and a breadth of 58 m. This Fairmount project was undertaken in two phases: tow out from the Tyne, and the ocean tow to Nigeria. During the preparatory period Fairmount personnel attended SBM facilities in Monaco, participated in river tow simulations at South Tyneside College and contributed to BITT team meetings in Newcastle, Monaco and Rotterdam.

Bonga was a manned tow. Prior to the departure from the Tyne, Senior Towmaster Bakker joined Bonga?s marine crew (also provided by Fairmount) for several weeks of intensive safety induction. This period was also utilised to fit towing gear and prepare life-saving equipment.

The three large ocean-going tugs arrived at Wallsend on September 30. October 2 was the planned departure date but unfavourable weather forced a two-week delay. The operational criteria for departure included: towout in daylight, passage through the Tyne breakwaters at high slack water during neap tides and a wind speed of less than 10 knots throughout the river tow. With the weather critical, Fairmount consulted a meteorologist ? who was on site two weeks prior to the initial departure date. The meteorologist stayed with the team for the river tow and the first leg of the ocean tow, to Las Palmas.

The river convoy departed on Sunday October 19. Bakker and the Marine Surveyor of the Port of Tyne Authorities agreed that the departure criteria had been met. Tugs and tow left the quayside at 07.25, with Far Saltire connected to Bonga?s bow, the Kotug rotortugs RT Magic and RT Spirit hooked up on the bow quarter and the Svitzer harbour tugs Ayrton Cross and Ormesby Cross on the stern quarters. In addition, Maersk Logger was stationed at the stern to act as brake tug during the river tow.

On rounding the last bend in the river the convoy was hit by severe squalls, with windspeeds of up to 37 knots during the passage through the breakwaters. Nevertheless, Bonga was taken through the breakwaters straight and true. Captain Bakker was waiting at the handover location three nautical miles offshore. He took command at 10.10 and the three ocean tugs took up their positions. The convoy sailed for Nigeria at 13.30.

Technical criteria for the ocean tow were established on the basis of a DNV Motion Analysis performed by Marin. Three towing draft cases were explored. The results indicated a required bollard pull of 293-313 tonnes, allowing for tug efficiency at 80 per cent (as provided for in IMO Maritime Safety Committee Circular 884 ? Guidelines for Safe Towage). The high bollard pull requirement reflected the need to take account of winds over the bow quarters up to 30 degrees. In these circumstances, however, the tugs reduce speed and this, in turn, reduces bollard pull. For this reason tug efficiency was calculated at 75%, producing a required bollard pull of between 306 tonnes and 319.5 tonnes. In the event, the tow was performed with generous reserves. The combined bollard pull of the three tugs was 527 tonnes. The convoy made fast passage through the Dover Strait, with speeds reaching up to 8 knots. They reached Las Palmas on November 6, for bunkering and a crew change for Bonga.

Advanced software

Lengthy preparatory work was also required for the transport of the 180 m long Frontrunner SPAR, undertaken on behalf of J. Ray McDermott. Engineering commenced in February 2003, utilising Safetrans for provisional calculations. Safetrans was developed by a group of 31 organisations with an active interest in heavy lift and towage.

Zhong Ren 3, 50,000 dwt, is the world?s largest semi-submersible heavy lift barge. Working in association with De Hong, one of the Fairmount-managed Chinese tugs, the tow speed of around 7.5 kts represents an effective challenge to self-propelled heavy lift vessels.

Detailed transportation engineering was undertaken with Marine Services Tool, a software suite providing calculations for the loading condition (including longitudinal strength) and environmental condition, together with motions and loads imposed on both cargo and carrier.

The skidding method was used to load the SPAR at Jebel Ali. The operational criteria were demanding with, for example, the vertical motions envelope at less than one inch at the stern. Yet the SPAR took just 13 hours to load, with Zhong Ren 3?s computerised ballasting system maintaining full control throughout.

The voyage to the USA began on October 10 and ended after 60 days with safe arrival at Pascagoula. The discharge operation was performed safely and smoothly, within the envelope set by the Marine Services Tool (which allows the hydrostatics of multi-body systems to be determined). Zhong Ren 3 submerged to 10 m depth above the cargo deck, allowing J. Ray McDermott to take delivery of the SPAR in a floating condition, for installation offshore. n