With the help of innovation from Norway the high cost of an unscheduled dry docking can sometimes be avoided. It depends on the work needed but for ship or platform operators with a sea chest or thruster tunnel problem, the name of Oslo-based Miko Marine should be music to their ears.

Miko has achieved prominence in this important sector due to its understanding and adaptation of magnet technology. Founded in 1996, when it launched its first magnetic patches, the company has evolved an entire magnetic product range that also includes lifting tools for ROVs (Remotely Operated Vehicles), mooring points, and tool fasteners which all exploit the power and versatility of permanent magnets. Miko employs a team of highly qualified and creative designers and engineers who are continually developing new tools and products to meet the specific needs of customers in the offshore and marine industries. They understand what magnets can and cannot do, how they will perform in a marine environment and how to handle them safely. It’s a hard-won specialism that is now paying dividends for Miko and its customers and for whom the design and manufacture of hull closures has become an important service.

Miko’s managing director, Cato Stoll, explained the thinking behind the demand for its hull closures. “Sealing any hull opening for internal repair or maintenance work has always been a technical challenge that invariably involves divers and underwater welding,” he said. “This work is expensive, slow and it can also be dangerous. This is why we are finding increasing numbers of operators ready to take advantage of what we know about hull closures, the use of magnets and their deployment by ROVs. When they realise that unless a repair can be made while afloat, the only alternative is to shoulder the expense of dry-docking. If this involves taking a vessel such as an FPSO (Floating Production Storage and Offloading vessel) off-station, there will be a major financial hit. By supplying hull closures that are easy and economical to use repeatedly and are, above all, safe and DNV qualified, we are able to solve some major headaches.”

It is this thinking that encouraged Japanese-owned rig and platform builder MODEC to commission Miko to supply four cofferdams and water inlet covers for its latest FPSO, currently under construction in China. On completion it will be operated by Equinor on Brazil’s Bacalhau field where it will be equipped to deal with any emergency relating to its hull openings.

Miko’s hull closures and cofferdams are all custom-built and use the most appropriate technology for the vessel. The Bacalhau project will feature Miko’s unique use of high-power permanent magnets to position and hold the closure in place.  Depending on its size, four to ten powerful Miko MAM permanent magnets are used to hold the cofferdam in place. With each magnet being capable of holding up to 2000 kg it is possible to achieve an immediate watertight seal for the closures without the need for any other fastening devices being fitted to the hull. Flotation material is integrated within the blanking plates and this makes them neutrally buoyant and easily handled and installed under water by ROV. Each magnet is attached to its closure by a flexible joint which enables the cover to be placed by the ROV and adjusted to achieve optimum seal. When the repair work is finished the magnets are simply freed by having the ROV rotate their release levers. enabling the blank to be quickly retrieved by crane and stored on board. The new sea chest inlet covers are scheduled for delivery in March 2021 when they will form part of the new FPSO’s equipment inventory remaining available for use throughout its working life.

A different approach was chosen for the Njord Bravo FSO (Floating Storage and Off-loading), refurbishment in Norway during 2019. For this project the curvature of the hull was precisely measured by laser scanner and covers were made for each of the four sea chests. For added safety two cofferdams were also manufactured to cover each pair of hull seals. On this occasion Equinor, which is both the owner and operator, agreed with Miko that magnetic fastenings should not be used for the Njord Bravo but chose instead hull closures that could be quickly attached by ROV to a specially designed interface fixed permanently to the hull.

The covers and the cofferdams were all made from aluminium incorporating neutral buoyancy foam. This enables them to be easily deployed by  ROV which benefits from an ingenious system of spring latches that enable it to lock the covers and cofferdams quickly into place against the interface and tighten the seal. Each component was subjected to detailed pressure and stress testing with the customer present to guarantee the integrity of the covers and their latches.

“Although Miko expertise is closely associated with magnets, we are used to solving other engineering and salvage problems where they are not used or needed,” said Cato Stoll. “The Nowegian Coastal Administration frequently invites us to solve specific technical or salvage problems but recently so much of our work has centred on the development of hull closures. Clients have a growing awareness of the time and cost benefits available when using magnetic fastening and we are continuing to expand our technical expertise to meet this demand.”