Mooring innovation puts flexibility front and centre

A shortage of vessels capable of large-scale mooring installations has led Kongsberg Maritime to develop a new system that allows offshore construction vessels (OSCVs) to handle more tasks independently.

The new solution has many benefits and features, according to Runar Hjelle, Kongsberg Maritime’s Sales Director for Offshore Construction & Support. 

He says: “Our new mooring capable solution integrates a purpose-designed anchor handling winch, shark jaws and stern rollers into OSCVs at the newbuild stage, enabling vessel owners to equip their ships for a broader range of mooring operations. It means OSCVs can handle more tasks independently.

By incorporating these relatively simple components, vessels will be able to perform pre-lay of mooring lines as a natural extension of their original subsea and suction anchor capabilities.

There are several benefits to having a mooring capable OSCV. Firstly, it allows vessels to carry out a larger portion of mooring operations, extending their operational capabilities and reducing the need for additional vessels at the field. This expansion of operational capabilities leads to significant synergies for the field developer, leading to cost efficiencies and easier vessel scheduling. Additionally, having winches and stern rollers enables safer and more efficient over-stern deployment of mooring lines.

The winch system can either be permanently installed or portable and loaded on board only when it’s needed, offering flexible installation options. The shark jaws and stern rollers are permanently fitted to the ship, taking up minimal deck space. Therefore, there is little impact on the ability of the vessel to carry out the subsea construction tasks it is designed to do.

The subsea crane, a common feature of OSCVs, can lift and install suction piles, as well as hold the load of the mooring chain. The baseline winch package includes one drum for work wire and two cable lifters for handling chain. However, additional winch capacity, such as increased capacity and active heave compensation, can be built into the solution, if needed. In combination with superior Dynamic Positioning (DP) capabilities and a large deck area, this makes for an efficient installation vessel.

The winch system is designed to handle high loads and operate in harsh offshore environments. It includes advanced control systems for precise handling of mooring lines and anchors. The shark jaws and stern rollers are engineered to withstand the rigors of offshore operations, ensuring reliable performance and safety. The combination of the mooring capable solution and the subsea crane, which is equipped with advanced lifting capabilities to easily handle heavy suction piles and mooring chains, further enhances the versatility of OSCVs.

Addressing market challenges

“In the years to come, there will be a lack of vessels with subsea crane and sufficient deck area suited to support the planned high volume of large anchors. With the addition of this system, OSCVs become a more attractive and efficient solution,” says Runar.

Several options exist for different vessel types. Firstly, for the conventional OSCV, it would be equipped with a large deck space and offshore crane, so it can install suction piles. However, connecting mooring lines to anchors often requires active heave compensation, which necessitates either an offshore crane or a heave-compensated winch.

High mooring rope capacities are also required, excluding many vessels currently in the market. A specialised mooring installation vessel, which typically features an offshore crane, significant engine power, bollard pull, and comprehensive winch and deck equipment package for mooring work, is the ultimate solution for large mooring installations. However, the building costs for such a vessel are high compared to a mooring capable OSCV.

Finally, for ad hoc OSCV mooring operations, such as hang-off frames, lay-towers and chain handled by crane, these operations are not standardised and often carry operational risks and inefficiencies.

Key components

A large deck space is required for anchors, equipment and reels. An offshore crane is essential for installing anchors, connecting mooring lines and lifting reels. A stern roller is necessary for the mooring line to pass over. In addition, tow pins and shark jaws control and secure the mooring line.

There is a winch with chain wheels and drum for handling chain and wire, lowering or recovering mooring lines, and holding chain weight. The winch is either low pressure hydraulic or permanent magnet motor electric.

Different deck layouts can ensure substantial fibre rope capacity. While OSCVs may lack sufficient bollard pull for traditional drag embedment anchors, they are well-suited for installing suction piles. Planning marine operations can address the need to pull the inverse catenary of the pile chain, which can be managed by anchor handling vessels during the hook-up phase.

These proposed adjustments to construction vessel newbuilds will position them to take on a larger portion of mooring line installations.

Runar adds: “These vessels have synergies with other field development activities, so the message to owners who are planning newbuilds is simple – why not make your construction vessels mooring installation capable?”

With this solution, OSCVs become a more attractive and efficient option for a broader range of mooring operations, ensuring reliable performance and safety in harsh offshore environments.