Motions. The single largest driver for the design of the vessel hull form is the response of the vessel to waves. The vessel must be designed to exhibit excellent response characteristics, minimum motions (displacements and accelerations) over the range of environments in which the vessel may operate.
The analyses and model tests confirmed the excellent performance of the vessel with 3 hour maximum pitch and roll angles remaining below 8｡?n the 100 year storm, whilst connected to the mooring. Roll angles in the disconnection condition are similarly modest. From a consideration of motions only, process plant can be expected to operate up to the 10 year return storm condition at these motion levels, if required.
Motions at the helideck are such that the helideck availability in clear weather is expected to reach 95%, with a minimum availability of about 90% in the worst month.
A summary of the maximum roll and pitch angles recorded in 3 hour duration storms is given in Table 4.
Green water. Green water, the phenomenon of a solid body of water impacting the vessel above the main deck, has the ability to cause damage to exposed equipment on any seagoing vessel.
To investigate this phenomenon for the Terra Nova FPSO vessel, a series of model tests were carried out at the National Research Council Canada's Institute for Marine Dynamics (IMD), in St. John's, Newfoundland and extensive analytical work was undertaken.
In the testing programme a total of 15 probes were mounted on the main deck to measure the incidents of green water.
In addition to the probes, video cameras were also mounted on the vessel model and at fixed locations in the basin. These video cameras were arranged to record the green water and ship motions from different angles. This provides a visual record of the green water events over the whole vessel. The video record can also be used as a check of the probe records.
The model test results were used as the basis for extensive analytical work to determine relative motions of the vessel and predict green water events over the full operating draught range and matrix of environments.
The probability of occurrence of green water during the lifetime of the vessel operation is evaluated as a function of a number of events, including;
Vessel heading.
Vessel draught.
Wave height.
Wave spectral peak period.
Life span of the vessel's service.
Green water, slamming and thruster emergence performance of the Terra Nova vessel are excellent. The bow design ensures that no significant green water occurs in any condition. The excellence of the vessel response in these extreme conditions can be judged from observations made during the 100 year storm tests, where the worst breaking wave crest approached the bow as a vertical wall at stemhead height - but did not overtop the bow.
Marine Equipment, Specification and Design General. The FPSO has 5×5 MW KaMeWa azimuthing thrusters, driven by ABB motors and controlled by a Simrad system to meet the Class requirements of Lloyd's Register of Shipping PM (T3) notation. With this configuration the FPSO will be capable of remaining on station in the 100 year return storm condition with a significant wave height (Hs) of 16.0 m and a maximum wave height of 30.4m.
Each of the 14 cargo tanks has an individual hydraulic submerged pump, supplied by Frank Mohn, with a capacity of 1,500 m3/h. Cargo can be offloaded to a shuttle tanker at a rate of 8000 m3/hr via a stern offloading system supplied by Hitec.
The ballast capacity is sufficient to avoid thruster emergence in all conditions, and here Frank Mohn pumps have also been specified (4×1000 m3/hr). These supply a common ring main providing a high level of redundancy. In accordance with C-NOPB rules, one ballast pump can be supplied from emergency power. Three deck cranes, two of 45 Te capacity and an aft one of 30 tonnes capacity have been supplied by Liebherr.
Two dual fuel Thomassen gas turbine driven generators each rated at 46 MW will be installed in Canada for main electrical power. The machinery spaces and accommodation are protected by a Semco high pressure water mist system, in lieu of a more conventional C02 system. A system of conventional fire hydrants, hoses, foam hoses and portable units is provided to meet all of the applicable regulations.
Aft Machinery Space. The main switchroom is located above the aft machinery spaces in the poop deck immediately aft of the principle gas turbine driven generators on the main deck. This switchroom contains 13.8 KV, 4.16 KV and 600 V boards. All power generation is at 13.8 KV. The power management system is supplied by Bailey systems and is compatible with the rest of the FPSO control system.
Apart from the main switchroom, the poop deck also incorporates the aft muster area and aft local equipment room.
The following major equipment is located in the aft machinery space;
-Two×10,000 m3/hr Smit inert gas generators. Capacity is set at 125% of maximum offloading rate. Both units have a turn down ratio of 7:1. Inert gas is supplied to all cargo tanks, slops tanks and all ballast tanks on the main ballast ring main.
-Two×2700 m3/hr Elliott air compressors. The instrument and service air system is common for all users on the FPSO. Primary user is the Topsides.
-Two×25 Te/h Aalborg boilers. These units are dual diesel/gas fuelled. They provide steam for water condensers, steam trace heating, cargo and ballast tank heating, Accommodation and machinery space Hvac heating. In addition a steam ring main is located on the Vessel and topsides to provide for steam lances used for ice clearance.
