Globetrotter I & II: Huisman’s successful shot at deepwater drill ship design and construction

With their first drill ship according to a new and innovative design running successfully for over a year and the second one nearing completion, Huisman from Schiedam, the Netherlands figured the time was right to introduce their Huisdrill concept to the world.

Drill ships are a difficult market, where conservatism rules and designs have hardly evolved over decades of experience. Nevertheless, Huisman, having ample experience in the design and manufacturing of heavy lift and offshore construction equipment, figured they could do better than the current state of the art by designing an entirely new drill ship from the inside out. Their design – named Huisdrill – managed to reduce the ship length by 20%, the lateral surface above the waterline by 50% and the height of the centre of gravity through various alterations. The result is a 46% smaller ship, requiring less fuel, a highly optimised drilling process and therefore lower operational costs.

Tough nut

The fact that the deepwater drilling market is a tough nut to crack is demonstrated by the fact that it took no less than ten years of intensive sales efforts before a client could be convinced to build a ship according to this new design. Although there is actually no new technology employed in the Huisdrill ship concept, it is the combination of Huisman’s technology in various related fields which makes it a winning proposition. Finally, in 2008, Royal Dutch Shell and Noble j ointly signed the contract for one drill ship with the new design: Noble Globetrotter I, shortly after followed by a contract for Noble Globetrotter II.

Naval architecture

The hull design is governed mainly by the requirement to provide a stable platform for drilling. The large beam of 32 metres, in combination with the low vertical position of the centre of gravity, results in a natural roll period above the wave periods typically encountered at sea. As a result, resonant roll is practically avoided and the rolling motions are very much limited. The diesel-electric propulsion system allowed the engine room to be positioned in the foreship instead of the common position below the aft deck. This created space under the aft deck to store riser joints in the holds below deck, thereby reducing the centre of gravity and the windage area. The 2,500 tons of riser pipe carried on board were lowered 15 metres, compared to a deck load.

Propulsion

The ship’s propulsion and dynamic positioning system works with six thrusters: three azimuthing thrusters in the stern and three retractable thrusters in the bow. As no retractable thrusters were available in the required size, Huisman decided to source conventional azimuthing thrusters and created

The Huisdrill concept integrates full functionality in a 46% smaller drill ship

the retractable mechanism in-house. The electric power is generated in eight gensets of 4.6 MW each.

Terminology

Typically the drilling process starts by first placing the blow-out-preventer on the seafloor (up to 3,000 metres deep) and then building up the riser pipe up from there. Once the riser pipe is completed, the drilling pipe goes down through it and starts drilling through the seafloor (up to 10,000 metres below the seafloor). Drilling mud, a mixture of oil and chemicals with the right weight to keep hydrostatic pressure on the well and to lubricate the drill, is injected through the core of the drilling pipe, and comes back up through the riser pipe. Onboard, this drilling mud is reconditioned for re-use in the drilling pipe.

DMPT

Perhaps the most visible difference to conventional drill ships is the compact drilling tower, consisting of a welded box girder type structure, rather than the truss constructions on other ships. This concept is called the Huisman Dual Multi Purpose Tower (DMPT). Housed inside the tower are the lifting winches and their heave compensation systems. A garage is built-in, allowing for offline maintenance of the topdrive in sheltered conditions. The pipe storage carrousels and drilling equipment are located on the outside of the tower.

A smart way to reduce the height of the drilling tower by about ten metres was devised by creating a liftable construction floor. The blow-out-preventer (BOP), a large subsea construction to be placed on the seabed, is stored on deck behind the drilling tower and can be moved sideways below this lifting floor. It is then lowered to the moonpool, where a cart can move the BOP forward to align with the drilling side of the tower. On conventional drilling ships, the construction floor is located above the level of the BOP, thus with a drill tower placed higher, and consequently a longer and heavier riser pipe, suspended from a higher lifting point.

The tower and its substructure were entirely built on the quayside in Schiedam. After testing and commissioning, the whole package was lifted on board in one single lift, which reduced the time needed along the outfitting quay. The tower head section is removable to allow sailing through the Panama Canal, the Suez Canal and the Bosporus.

Layout

The deck layout is such that the forward side of the drilling tower is the actual drilling side, with an iron roughneck on deck connecting the sections of drilling pipe, with minimal manual labour. These sections are pre-assembled per three 14 metre pipes on the aft deck into 41 metre long pipe sections. They are lifted upright and placed into the carousels on either side ofthe drilling tower, from where they can be picked up on the forward side. This configuration allows for the offline pre-assembly of the pipes on the aft deck while sailing or even during drilling on the forward side.

Heave compensation

Both the riser (when completed) and the drill are heave-compensated during operations. This keeps the pressure on the bottom constant, regardless of the ship’s motions. The system allows for drilling to carry on in sea states with a significant wave height of up to five metres. If the weather further deteriorates, the drilling operation has to stop and the vessel has to remain ‘waiting on weather’. Beyond significant wave height of eight metres, the vessel has to disconnect. On board there are two ROVs (remote operated vehicles), of which one is a working class ROV and the other an observation ROV.

Splittable blocks

A Huisman innovation in the lifting equipment consists of ‘splittable blocks’. By choosing the amount of pulleys in use (moving along with the moving part), the same winch can either

Because of the dieselelectric propulsion, space was created for the riser joints below the aft deck

move heavy loads very slowly or light loads very fast. The redundancy is ensured by the fact that the wire is wound onto a captive winch at either end. Normally both winches work together, but if one should brake down, lifting operations can continue at full load, but at half speed.

Simulator

The drilling process, including operation of the iron roughneck, is monitored from a control cabin on the drill floor. For training ofthe drilling crew before going on board, Huisman built a complete copy of the cabin with all controls and a large projection screen of the action on deck. Besides the training, the simulator also allows for the automation software to be checked and tested before installation on board.

Construction

Globetrotter I and II were both built as empty but working ships at STX Shipyards in Dalian, China. After completion, they sailed to Schiedam, where the drilling tower, the substructure and all associated equipment was installed. As with most of Huisman’s production, most of the structural parts of the tower were prefabricated at their facility in the Czech Republic and then transported over the road to Schiedam for assembly.

Conclusion

Because of the different type of drill tower, the diesel-electric propulsion system and the liftable construction floor, Huisman’s engineers managed to obtain the same drilling performance in a significantly smaller ship, with smaller thrusters and less fuel consumption. Noble Globetrotter I is currently in operation in the Gulf of Mexico, while Noble Globetrotter II will shortly sail to Benin, on the West coast of Africa. Both ships are hired in ten year contracts, a proof of the confidence Shell has in this concept. In the meantime, work at the Huisman yard in Schiedam is in full swing on five pipelay spreads, with another in the prefab stage in the Czech Republic. A heavy-lift crane for a French port is also in production.

Bruno Bouckaert