Successful full size trial of ShipArrestor

Miko Marine AS of Oslo has successfully completed the first full scale test of its pioneering ShipArrestor system.

The system enables a helicopter to attach a sea anchor on a tow line to an unmanned vessel such as a tanker that is drifting without power. By reducing the speed of the ship’s drift, the ShipArrestor increases the time available for rescue tugs to reach the vessel before it runs aground with potentially severe environmental consequences.

The trial was undertaken by Miko Marine in association with the Norwegian Technical Institute and Norway’s Coastal Administration. It took place recently off the north coast of Norway using the 120,000 ton LNG tanker Arctic Princess, which was made available by Hoegh LNG and Statoil.

The tests were conducted in two phases, the first being with a helicopter operated by Luftransport that successfully ‘lassoed’ the winch gear and bollards on the foredeck of the Arctic Princess. This was easily accomplished with a replica of the connecting ring and the lightweight chain that will be used in reality. Although it had the weight and handling characteristics of the real chain, it was decided that a mock-up should be used to avoid the chain causing damage to the forecastle of the Arctic Princess. The helicopter pilot encountered no problems attaching the tow line to the ship and in releasing it correctly, and Claus Christian Apneseth, project manager for Miko Marine is now confident that it is a viable procedure.

‘The weather during the trial was very benign and it would have been interesting if it had been more demanding, he said. ‘Our pilot had no difficulty placing the ring but he was confident that the operation would remain feasible in rougher conditions. Although they would have been more of a challenge, it was probably better that our first full scale trial was performed in manageable conditions.’

The second phase of the trial was completed shortly afterwards. It tested the performance of the sea anchor itself and was completely successful. A 30m diameter nylon parachute anchor was deployed from the Arctic Princess by a tug. It then turned the LNG tanker up into the wind in less than 20 minutes and reduced its rate of drift by 58%.                

‘We have identified some small design improvements that can be made to the anchor, but in a genuine emergency its performance could have been the difference between the successful recovery of an oil tanker or its being wrecked’, said Apneseth. 

The concept of the sea anchor is already well known to seafarers but, until now, its use has been restricted to smaller vessels. Part of the project has been to include the mathematical modelling needed to identify the size of sea anchors needed for ships of different tonnages. This impacts upon the sea anchor’s weight and its ability to be carried by helicopter. Similar constraints apply to the tow line, which must be strong and also capable of resisting abrasion against the ship’s winch and gunwhale. This has led to the development of a unique lightweight chain that is half the weight of conventional chains offering the same performance.

It is also believed that the research will lead to the development of sea anchors that can be permanently carried aboard ships for emergency use. The  recent loss of a  jack-up platform for windfarm installation from a heavy lift vessel when its engines failed in mid-Atlantic is a demonstration of the dangers arising from excessive roll when a ship is unable to turn into the wind. Miko Marine is confident that a solution now exists for this type of hazard.

Miko Marine holds the patent for the ShipArrestor principle, which is being developed with help from an EU investment grant and a consortium of eight European organisations. This includes companies from Norway, France, Germany, Netherlands and Austria as well as the Norwegian Institute of Technology and the UK’s Ship Stability Research Centre. It is now hoped that the Norwegian Coastal Administration will become the first to buy ShipArrestors, which it would be expected to keep at its depots around the Norwegian coastline. They would then be readily available in an emergency and could reduce the likelihood of groundings and the pollution that can result from them.