Far Samson is a powerful new offshore vessel designed and equipped by Rolls-Royce now being put into service by Farstad Shipping of Norway.

Rolls-Royce developed the special design, working closely with the owner and charterer, and this UT 761 CD has been built by STX Europe (formerlyAker Yards Langsten, and goes on long term charter.

Far Samson is thought to be the most powerful offshore vessel so far, with a continuous bollard pull of 423 tonnes with auxiliary thrusters operating and 377 tonnes under main engines alone.

The UT 761 CD is a design specially developed to meet a strict set of requirements from the owner and charterer, and incorporates new technology. It is a multifunctional vessel capable of carrying out heavy ploughing operations for pipes and cables on the seabed, sub sea installation work in ultra deep water, ROV operations, towing, and other challenging subsea operations. The specification calls for ploughing to a cut depth of 2.5m in the seabed in water up to 1,000m deep.

Meeting the various demands means a large vessel, 121.5m long overall, 26m beam, 12,000 gross tons, the hull strengthened to Ice Class 1B, having also DeIce Class for operation in iced waters and harsh conditions. Hull lines are optimised for the required 12-17 knot transit speed range, allowing the ship to mobilise efficiently for operations anywhere in the world. The top speed is more than 19 knots. The draught is approximately 8 m to give sufficient immersion to the large propellers. The hullform incorporates a bow bulb and stern sections designed to give a clear flow of water to the propellers to satisfy the requirement for an extremely high bollard pull.

During design and construction of this Clean Design vessel, utmost attention was paid to internal and external environmental aspects as well as the safety conditions for vessel and crew.

An unusual feature of the UT 761 CD is two working deck levels. The space over the main deck houses the winches (Rolls-Royce 600tonne pull hydraulic main winch) and is open at the stern, allowing wires to be run over a stern roller. It is flanked by workshops and winches for the A-frame. In the deck are towing pins, shark jaws and centring devices for controlling the tow wire. Above it is the working/weather deck fitted with a track system and transportation skids for deploying either of the two massive ploughs offshore. An A-frame with a 250 tonne safe working load offshore and active heave compensation is mounted at the aft end of the deck. Between the working deck and the accommodation is a large ROV hangar. A 7.2m x 7.2m moonpool is provided amidship with a hatch in the work deck and with a closable hatch at the bottom to prevent sea water pumping at the high transit speed. Equipment can be deployed through the moonpool using the offshore crane, which is rated for a 250 tonne lift at up to 35m outreach and 3,500 m working depth. Because of the high asymmetric loads, the ship will have an active heel control system as well as passive roll reduction tanks. For special operations a tower can be installed on the working deck above the moonpool. Ahead of the plough garage is an ROV hangar and deployment system.

Far Samson has a hybrid propulsion combining diesel electric and diesel mechanical transmission to give optimal operating flexibility, fuel economy and minimum exhaust emissions. Depending on the type of operation, the UT 761 CD can run in any of six principal propulsion modes. This flexibility means that the widely varying power requirements are efficiently catered to, there is a high level of propulsion redundancy, and engines are run at an efficient part of their load range, minimising exhaust emissions. All Bergen engines meet Clean Design class rules without further exhaust clean-up, but catalytic converters are additionally fitted to the gensets, giving 95% NOx reduction.

To meet IMO DP3 requirements the machinery is split between two engine rooms separated by a longitudinal watertight bulkhead. Each of the two main CP propellers is turned by two Bergen B32:40 V12P engines, coupled by a twin input single output gearbox, to give 12,000 kW per propeller. Each gearbox also has power take-off and take-in for respectively a shaft generator and an electric motor. There are four auxiliary generator sets each powered by a 9-cylinder Bergen C25:33 engine.

The main 5.4m diameter CP propellers in nozzles with their independent flap rudders are supplemented by several Rolls-Royce thrusters. Aft are two 1,200 kW tunnel thrusters and an 1,800kW swing up azimuth thruster. Forward there is one 1,800kW tunnel thruster, a swing-up azimuth unit of the same power and an 1,800kW Combithruster which when swung down operates in azimuth and when housed forms a tunnel thruster with no projection below the hull.

One major role for the new Farstad vessel will be pipeline trenching. The charterer is a leading specialist in this type of work and has developed a new generation plough that is capable of cutting a 2.5m deep trench in the seabed, compared with the 1.5m typical previously, allowing for larger pipe diameters and giving the pipe better protection. Far Samson can pull this plough in the water depths that will be called for in the future. The main plough cuts the trench and places the pre-laid pipeline in it in one operation and a separate backfill plough is used later to backfill the trench.

When not in use the main plough is housed in a large hangar on deck where it can be maintained under cover. The hangar is detachable, so that if the plough is not required on a mission it can be stored ashore using the hangar as a garage.

To move these heavy pieces of equipment on deck safely and under full control, Rolls-Royce has developed a special skid handling system allowing one plough to be parked on the centreline under the hangar, the other overhanging the deck edge to port. Being able to change the ploughs offshore, eliminating the need for port call for plough change, as well as being able to carry both ploughs in fully operative condition on deck at all times, will be a great advantage for the operation.

Far Samson has accommodation to Farstad’s high standard meeting Comfort class (V3)(C3) rules. Since the type of operations to be undertaken involve large numbers of people, a total of 22 single cabins and suites and 39 double cabins are provided, together with all facilities including messes, cafeteria, dayrooms, gymnasium, hospital, offices and conference rooms, spread over six decks. There is a central lobby and lift to the various levels, while the layout allows easy movement of people around the ship.

A distinctive feature of the design is a double deck bridge layout. The navigation wheelhouse follows current UT-Design principles, with a semicircular bridge front and the main forward facing control station for transit and navigation placed for optimum sight lines. Communications and a client/ROV service area are located in the centre with the casings either side, and at the aft end, commanding a clear view over the deck and the area around the ship, is the manoeuvring console.

On the deck below is a second set of consoles enjoying a good view over the working deck, from which ploughing and other winch operations can be controlled. DP3 and other controls are also slaved to this position. On the same deck is a plough/control/survey space, an instrument room, suites of offices and a conference room. There is a separate ROV control room, and a new engine control room concept has been developed particularly for this vessel.

Immediately after delivery from STX Europe to Farstad, the vessel will start its long term contract. Far Samson will pick up the ploughs and use the first period for commissioning tests and mobilisation. Various projects such as subsea support, ROV support and craneage work have been scheduled in between the ploughing operations.

This is a large, expensive and complex vessel. But Farstad was building on experience in deep water ploughing from another vessel designed and equipped by Rolls-Royce and built at the same yard, the UT 741 Far Sovereign. With a bollard of 280 tonnes this is a less powerful vessel, but it has for many years handled deep water ploughing giving great satisfaction, trenching to what has been up to now the normal depth of cut of 1.5 metres in up to 500 metres water depth.

Text: Richard Childs
Reprinted by permission from Rolls-Royce

Date: 25 June 2009