Fugro adds new clean-design Class C seismic vessels
Martin Hartland, David Nolan - Fugro-Geoteam
Fugro has added two new C-Class seismic vessels to its fleet. Both are designed for challenging offshore areas and both can tow up to 16 seismic streamers on dedicated streamer winches with a capacity of 8,000 m (26,246 ft) of cable.
TheMV Geo Caspian and the MV Geo Coral have the class designation of “Clean” and “Clean Design,” which means they comply with the highest environmental standards and have a double skin in the area of the fuel tanks. The class notation covers emissions of any material with global warming potential (GWP), including fire fighting chemicals, refrigerants and fuel. Geo Caspian is the world’s largest Clean Design seismic vessel.
Both vessels were built in Norway to Fugro-Geoteam specifications. Each is just over 108 m (354 ft) long with a 28-m (92-ft) beam and a GRT of 12,600 metric tons (13,899 tons). They will be the slightly larger sisters of theGeo Celtic and Geo Caribbean already in operation with Fugro. Fugro formally took delivery of the Geo Caspian in March and the Geo Coral was scheduled for delivery at the end of July.
Seismic specifications
The vessels are rigged to tow up to 16 solid streamers with the potential to achieve an overall spread of 1,500 m (4,921 ft), and dual sources each up to 5,100 cu in each. The wide tow is achieved using Baro 410 deflectors made by Baro Mek Verksted in Norway. These 11.3-m (37-ft) high deflectors, with a weight of 12 tons each, require robust handling and towing systems. They have a high level of redundancy and can handle the high forces experienced when recovering during severe weather.
The latest Sercel Seal 428 recording system allows continuous recording of seismic data, eliminating dead time between data. This is expected to be a great benefit during complex surveys using several vessels, such as wide-azimuth and undershoots.
Purpose-built in 2010,Geo Caspian is the world’s largest Clean-Design seismic vessel and a key new asset in Fugro’s fleet.
All Fugro vessels have Fugro’s Fresnel Zone Binning which can position the streamers to optimize subsurface seismic coverage and to minimize infill. Use of lateral steerable birds also has proven successful for 4D purposes in obstructed areas or when applying new acquisition techniques such as shooting in turns or in fan-mode. Other benefits of the lateral controllers include more efficient equipment deployment and recovery, and safer work boat operations because of improved streamer control.
Unique to the C-Class vessels is the use of electric drives on the winches and handling systems using vector control technology. This gives an accuracy of 0.01% compared to 5% on traditional large-scale hydraulic installations. This control during deployment and recovery shortens installation times and reduces operational issues.
The energy source uses up to 84 “G Guns” deployed on six 20-m (65.6-ft) long stiff gun arrays. Control of the source is from the Gun-link 4000 digital distributed system, which allows the C-Class vessels to use gun umbilical cables of 800 m (2,625 ft) lengths. This allows Fugro-Geoteam to offer reduced in-line offsets (source to receiver).
Communications are maintained to shore by two V satellite systems situated to ensure communication on all headings at high latitudes. An additional KU band antenna also is installed.
HSE
Deck areas are arranged for maximum work space and clear visibility, and the handling equipment throughout the vessel is designed to lower risk for personnel injury.
There are offices for the ships’ officers and senior survey specialists, and these are supplemented by large conference rooms. Crew accommodations include 70 single cabins all with private bathrooms; a 70-seat cinema/auditorium; a fully equipped hospital; a gymnasium; and a swimming pool.
The comfort and vibration levels as defined by the classification society are V(3) – C(3), which is a high standard for an offshore service vessel.
The bridge is designed and classed according to NAUT-AW rules which aim to improve nautical safety and to reduce the risk of failure in bridge operation which could cause collision, grounding, or heavy-weather damage.
An integrated helicopter deck on the fore part of the ship is built to the UK CAP 437 rules for a Sikorsky S92 helicopter. Adjacent to the helicopter deck is a hospital managed by a professional medic.
Marine specifications
Main propulsion is diesel-electric with conventional variable pitch and variable speed propellers. The diesel-electric system also uses vector control technology to optimize setting during towing operations for reduced fuel consumption and emissions for a given towing force. C-Class vessels have a Bollard pull greater than 150 metric tons (165 tons) on the main shafts only. The retractable 360º azimuth thruster in the fore part of the vessel provides additional towing force and propulsion redundancy.
The main generator sets use medium speed engines by either Rolls Royce or Wartsilla, and power onboard is handled through a power management and automation system with operator stations on the bridge console and the main control room. The automation systems have been evaluated using “hardware in loop” testing (HIL). This assists Fugro Geoteam in risk management related to automation.
Remote dial-in diagnostics are in place for trouble shooting by shore-based specialists of automation issues on the vessel’s critical systems.
The compressed air for the seismic source is provided by three LMF compressors with an output of 2,190 scfm each and with delivery pressure up to 3,000 psi. They are electrically driven variable speed units which reduce emissions as only the amount of air needed for the source is compressed. Sensors and the automation system control the speed of the compressors to maintain pressure and flow at the optimal level.
There are five boats onboard, including two lifeboats with capacity for the complete crew within each boat, a high-specification 7.5-m (24.5-ft) fast rescue craft (FRC) and two 9.6-m (31.5-ft) seismic workboats. The seismic workboats have a top speed of 25 knots and can carry two sections of seismic streamer. They also have twin engines and additional tools built into the design to facilitate in sea replacement of damaged sections within the streamers. The seismic workboats are recovered into recesses for weather protection of the crew when performing maintenance. The davit system uses a passive shock absorber to reduce stress during handling.
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