DCV AEGIR: A State-of-the-Art Workhorse

It is always good when a ship’s owner secures a contract for the use of the vessel before it comes into service. Usually this happens towards the later stages of the build of the vessel. It is indeed unusual for a vessel to have two contracts for its use secured before the detailed design is even finished and the building has commenced. This is not a matter of luck or good fortune, but rather the result of a careful investigation into the industry’s requirements and a tailored solution design to meet them.

The vessel in question is the Deepwater Construction Vessel (DCV) Aegir, a collaboration between Dutch companies Heerema Marine Contractors, Ulstein Sea of Solutions (design), Huisman (lifting gear and pipe lay tower), Remacut of Italy (pipe multi-jointing equipment) and Daewoo Shipbuilding & Marine Engineering (DSME, vessel construction) in South Korea. Aegir, owned by Heerema, is capable of pipe laying, subsea installation work and heavy lift construction work. Initial talks between Heerema and several design companies commenced in 2007 and explored a number of options, such as a semi-submersible vessel with several laying options, but in 2010, the decision was made to go ahead with a monohull deepwater construction vessel, which resulted in the design for Aegir.

The Heerema – Ulstein Synergy

Ulstein Sea of Solutions in Vlaardingen, the Netherlands, who recently celebrated their 12.5-year anniversary, pride themselves on their custom design capability and experience, and relished the chance to challenge familiar solutions and employ ‘state-of-the-art’ equipment. Hence, they were pleased with the prospect of being able to develop the Ulstein SOC5000 concept to a new level. Ulstein was awarded the design contract in January 2010 with the somewhat unusual stipulation, that Heerema would select the shipyard to build the vessel and have a signed letter of intent by 15 July 2010. Only three years later, on 20 September 2013, Heerema hosted a party to celebrate the naming of Aegir, which left Rotterdam on 29 September for her first job.

Heerema has been a major player in the high tech field of pipe laying and underwater construction for many years. The company was well aware that the future of deepwater production promises much growth and technical development. However, an investment in these financially uncertain times is not risk-free and requires fresh approaches to justify it. It is a fact that the continuing demand for oil and gas is pushing the industry to tap into resources further offshore and in ever deeper water. This brings with it another set of challenges that the industry has to overcome and vessels need to be designed to anticipate and accommodate these developments. The fact that Aegir s first contract in the Gulf of Mexico and the following contract in Western Australia were awarded long before the vessel had been fully designed and built is a testament to the fact that the Aegir is the solution to such challenges.

At 211.50 metres overall length, the design of Aegir is based on the Ulstein SOC5000 design, albeit much modified and customised. The initial design of the vessel was handled by Ulstein, while the overall design phase consisted of four parallel evolutions: the shipbuilding (DSME), the offshore mast crane (Huisman, China), the multi-joint pipe handling plant (Remacut, Italy) and the Multi Lay System (Huisman, the Netherlands). Working in such a way was necessary to ensure the successful integration of what was by definition going to be a complex vessel. In fact, the development and manufacture of the pipe laying and handling equipment, cranes and lifting gear took more time and money than the vessel itself.

The cranes, deck tracks and pipe lay tower foundations were installed on the vessel at the shipbuilders in Korea, the vessel was then sailed to Schiedam where the rest of the pipe laying and handling equipment was fitted before sailing to the Caland Canal in the Port of Rotterdam for completion and preparation for trials.

Concept studies and the basic ship design

Initial studies of working procedures indicated that a single multipurpose vessel which, when supported by other vessels, could stay ‘on station’ would be more cost-effective than a vessel returning to port to load more materials over the increasing distance entailed by working fields further offshore. The solution was a vessel capable of embarking heavy loads in the form of straight pipes, pipe reels and other equipment whilst at sea allowing the other vessels to ferry materials out to it. This, when coupled with a relatively high transit speed, would allow the vessel to get from site to site (contract to contract) quickly and thus most cost effectively. The fact that Aegir can be used for J-laying, Reel-laying and deepwater construction – after a reconfiguration which takes hours rather than days – means that usually a different activity can be scheduled instead of waiting for a supply of pipe material.

The vessel itself is a DP3 monohull built under the Special Purpose Ships (SPS) code, whilst at the same time complying with the requirements of the Norwegian Maritime Authorities (NMA). These strict rules include, amongst others, following passenger ship requirements resulting in tighter stability requirements especially during lifting operations and a special ‘Evacuation Analysis’. The safety equipment includes six totally enclosed Norsafe lifeboats type JYN100 with a single pivot davit with onload release hook system and two fast rescue boats with luffing davits.

Aegir has accommodation for between 289 and 305 crew, subject to whether the client requires NMA compliance, which maximises the occupancy at two per cabin. In other cases, eight of the cabins can be occupied by four people, which increases the total capacity by 16 people. The bridge is in effect two bridges. The forward facing part is used solely for sailing the vessel from A to B and the aft facing one is where all the survey, ROV, DP and pipe laying and lifting activities are controlled.

Power is generated by six 8,000 kW Hyundai diesel generator (DG) sets, grouped in pairs and connected through three main switchboards in three separate watertight compartments. The DG sets themselves are located in two engine rooms, separated by a watertight bulkhead on the centreline. The vessel also has a 1,600 kW emergency DG set installed above main deck.

Main propulsion is provided by two fixed pitch/ variable speed azimuthing propulsors of 6,500 kW rating each. For dynamic positioning, an additional four 3,200 kW retractable azimuthing thrusters are provided. All six azimuthing thrusters can be demounted without dry-docking the vessel. This is achieved by storing a pair of cofferdams in each of the thruster rooms, to close both the top of the thruster and the hole in the ship. An added benefit, next to the possibility to avoid expensive drydocking in some cases, is that during regular drydockings, the ship does not need to be docked on four-metre high keel blocks, as a defect thruster can be taken out before the docking. The system was devised by Heerema in collaboration with Rolls Royce, the supplier of the thrusters. A 2,500 kW tunnel thruster in the bow is used for harbour manoeuvring and in dynamic positioning mode.

Lifting gear and process

The first challenge in the solution described above is that of loading the Aegir from the support barges. For this, a large main crane was required which would have a significant impact on the stability of the vessel, especially when transfers are conducted at sea. The first issue is the location of the 4,000 mt Huisman offshore mast crane itself: for maximum accessibility the aft corner of the deck allows the largest outreach over the side of the vessel, so the starboard aft corner was selected. This presents its own issues, as the structure at the end of the vessel is not as strong as the structure amidships, because there is less ‘tie-in’ structure around it, so an element of strengthening had to be introduced.

The deck layout was driven by the offshore mast crane, which had to be placed at the stern to allow for offshore construction work over the stern. To avoid a conflict with the multi-lay tower (which tilts towards the stern for pipe-laying), the crane was moved to starboard and the multi-lay tower and the moonpool beneath it placed on portside of the centreline. The reels are mounted on sliding tracks just in front of the mast crane. There is space for three reels: a full reel on starboard as reserve capacity, a reel in use near the centreline (in line with the multi-lay tower) and an empty reel on portside.

The location of the reels, near the offshore mast crane to enable offshore loading and unloading, dictated that the pipelay tower had to tilt towards the aft and that consequently, Aegir will always be sailing astern when pipe laying from the reel.

Conveniently, the mast is located on starboard, so the lightest loads (the empty reels) are lifted with a longer outreach and the heaviest loads (the full reels), with a short outreach. The crane is designed for two times 2,000 mt split lifting, this offers the ability to upend piles and structures. The hook can also be fitted with a 4,000 mt swivel block, so that while the crane turns the orientation of the lifted equipment in relation to the vessel can be maintained.

The auxiliary hoist on the main crane, and the portside A&R/deep water lowering wire are both heave-compensated. Continuous and safe reel transfer at sea is supported by Aegirs unique reel handling system using a novel system of damped horizontal tugger lines. By minimising the swinging of the heavy load suspended from the crane, and forcing it to move in unison with the vessel, these tugger winches dampen the entire ship’s rolling motions with great effect. The damping effect is achieved by varying the pulling force on the tugger winches as the lines get paid out or hauled in. The system was tested and fine-tuned with model testing in a wave basin.

To compensate for the stability changes when loads are assumed, there is a smart anti-heeling system comprising of ten ballast tanks in the hulls of the vessel, arranged in five pairs. Between each pair of anti-heeling tanks, three 1,500 m3/h pumps ensure quick transfer of ballast water from port to starboard and vice versa. These centrifugal pumps are frequency-controlled, allowing them to maintain a specific differential of head between the tanks, without closing the cross-over valves. The system is driven by smart modelling software that anticipates the expected angles of heel, based on crane movements rather than actual heel angles.

Another feature is ‘weather vaning’ which will decrease the roll. A V-lay stinger, located at the bottom of the moonpool, allows the Aegir to lay pipe at an angle to the ship’s heading, thus allowing the vessel to keep her bow to the weather while travelling sideways.

J – Laying (J-lay)

Aegir has two options of pipe laying: J-laying and Reel-laying. In practise, the two laying systems cannot be used together so the tower and deck are configured for whichever option is being used at that time.

In J-lay mode, the pipes arrive at the vessel pre-assembled as ‘quads’, which consist of four pieces of pipe with a total length of 48 metres. The pipes can be either single-walled or double-walled. From starboard, the quads are transported to the PS main deck and further aft on rollers to a tilting platform known as the Quad & PLET Loader. Once in place and aligned the Quad & PLET Loader is tilted up to align with the tower. The tower stands over a moonpool in which the previously installed pipe is retained on a hang-off clamp. When the new section is in place in the tower it is aligned with the section in the hang-off clamp, prepared, welded and coated and fed down through the moonpool as the vessel moves astern and the process is repeated.

The effective moonpool measures 25 metres long by ten metres wide, a sufficient size to allow passage of not only the pipe, but also of the Inline Tee Assemblies (ITAs) and Pipeline End Terminations (PLETs), the fittings that are used at the beginning or end of a pipeline.

When the vessel is J-laying, the pipe reels and transportation system are stored off the ship to create space for the storage of new pipe lengths. When laying pipe in deep water, the tower stands vertically and the J-shape adopted by the pipe as it approaches the seabed has a radius large enough to not buckle the pipe. But, when laying in shallow water, the radius is not large enough and would cause deformation to the pipe. To accommodate this, the tower can be tilted backwards up to 65o to decrease the sag bend radius.

Reel laying (R-lay)

When reel-laying, the friction head clamp, the loader extension and the quad feeder are removed from the ship, and the reel-laying parts brought back on board. The reels themselves have a 16 metre drum and 2,000 tons pipe load capacity making Aegir one of the largest reeling ships in the industry. For an eight-inch pipe, this corresponds to about 21.5 kilometres. In this process, a reel is aligned with the laytower, the pipe comes off the reel in the direction of the stern of the vessel and arches up to the top of the tower. Here it goes through the aligner reel and then through a straightener and two tensioners. Dictated by the water depth, during reel-laying, the tower is also tilted back to reduce the pipe angle at the top of the tower.

Abandon and Recovery/Deepwater lowering system

A situation that confronts all pipe and cable layers sooner or later is the need to leave the pipe or cable before a severe storm and then return when the weather moderates. Sometimes a pipe has to be picked up which has been laid by another ship, or the pipe has to be lowered to the bottom when the job is completed. This process is known as Abandon and Recovery (A&R). To effect this operation, the pipe end is terminated and lowered to the bottom through the moonpool, its location accurately monitored and recorded before the vessel departs the site. Once the weather has improved, the vessel returns and, using the DP system, the end of the pipe is recovered through the moonpool with the A&R system. Two A&R winches are installed below the main deck, one of which is heave-compensated. Each of the A&R traction winches feeds the wire to a storage drum with capacity for 7,000 metres of 126 millimetre cable.

When a pipe has to be raised from the bottom and connected to an FPSO platform nearby, it will be raised by the A&R system and then handed over to the offshore mast crane a few hundred meters below the water surface. The A&R and deepwater lowering system was supplied by Huisman Equipment. The A&R winches also serve as a deepwater lowering system for the installation of subsea structures at water depths greater than 300 metres.

RQUs

DCV Aegir is equipped with two ‘work class’ Remotely Operated Vehicles (ROVs) complete with their own launch and recovery systems (LARS). They are located just aft of the superstructure to port and starboard side in their own dedicated hangar and maintenance facility. The ROVs are capable of working to a depth of 3,500 metres, within a radius of 1,000 metre. ROVs are used for a wide range of tasks, such as pre-lay surveys or touch-down monitoring. They are the hands and eyes of Heerema under water. One of these tasks is the ability to follow a pipe for survey purposes. In this case, Aegir s DP system can be set up to follow the lead of the ROV without any crew or pilot input.

Conclusion

The Aegir is a multipurpose deepwater construction vessel, designed to meet a wide range of demands of complex deepwater projects under a single contract. The DCV concept offers a full range of facilities, capable of executing complex infrastructural and pipeline projects in ultra-deep water and sufficient lifting capacity to install fixed platforms in relatively shallow water and structures in deep water.

The vessel’s multi-laying capabilities enable the Aegir to install heavy deepwater trunk lines and pipe-in-pipe assemblies by J-lay or reeling operations in depths of up to 3,500 metres. The design allows for easy and fast mode changes from reel-laying to J-laying or deepwater construction and vice versa, ensuring that the maximum amount of jobs can be taken on and the ship’s planning calendar shows minimal blank areas.

The loading system for the reels ensures that the vessel will be doing mostly what it is built for (pipe laying) and will spend a minimal amount of time on what can be done by almost any vessel: spooling and shipping reels. Parallel with Aegir, Heerema has commissioned two reel-transportation barges, two tugs and three reels. The transit speed of the vessel, in excess of twelve knots, guarantees flexible operations all over the world. Summarised in a few words: ‘A versatile Swiss pocketknife, among the Heerema Sea Giants’.

Tom Oomkens, Andrew Rudgley & BrunoBouckaert