Ship Arrestor – Dropping Giant Sea-Anchors Via Helicopter To Assist Salvors

The ShipArrestor, chosen from among 1200 projects funded by the European Union, defends coastlines against environmental damage when a drifting oil tanker runs aground. A consortium of eight European organisations was created to develop the ShipArrestor idea under Miko Marine’s leadership and was partly funded under the European Union’s Research, Innovation and Competitiveness Framework programmes.

The project consists of organisations from France, Germany, Netherlands and Austria including The Norwegian Institute of Technology and the UK’s Ship Stability Research Centre. By applying their expertise to the challenge, they have developed a technique to enable a tow line to be attached to a drifting drifting ship by helicopter. The tow line leads to a sea anchor that is able to halve the speed of the ship’s drift creating more time for a rescue tug to intercept the vessel before it runs aground.

It is not unusual for ships to lose engine power at sea and the consequences of them running aground can be disastrous to the environment. The introduction of a method for regaining control of such ships is now being seen as an important new option for coastal administrations. The British Isles are seen as being at particular risk due to the loss of funding for the UK’s four Emergency Towing Vessels (ETVs). The ShipArrestor is consequently being cited as a solution that would enable fewer rescue tugs to service the same area at significantly lower cost.

Miko Marine has developed the ShipArrestor techniques and hardware so that a conventional search and rescue helicopter can deploy a tow line around the winch gear on the foredeck of an abandoned vessel. The helicopter then lays the line upwind and releases it attached to a sea anchor. Full scale tests have demonstrated the system’s effectiveness and in one trial a 30-metre diameter nylon sea anchor was able to turn a 120,000 ton LNG (Liquefied Natural Gas) tanker into the wind and slow its drift by 58 per cent. This could prove vital for improving the chances of survival for a ship in danger of being blown ashore and also for the safety of the cargo and crew of a ship rolling in a heavy sea.

Part of the project included 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 subsequently led to the development of a unique chain that is half the weight of conventional chains offering the same performance.

The ShipArrestor project could also lead to the permanent carriage of sea anchors aboard ships for emergency use. The need was recently demonstrated when a windfarm jack-up platform costing millions of dollars was lost from a heavy lift vessel when its engines failed in mid-Atlantic. The incident demonstrated the dangers of excessive roll when a ship is unable to turn into the wind and Miko Marine is confident that it can now provide a solution for this type of hazard.

With its development programme complete The ShipArrestor is now being offered to national maritime administrations that have a need to protect their coastlines against the high cost and the liabilities that can arise from large ships grounding within their areas of responsibility. The Norwegian and Swedish coastal administrations are actively considering its use and the German Havari Kommando Nord is planning tests of a version modified to its own requirements early in 2012.

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