The delivery of the emergency tug 'Nordic' this year illustrates a growing focus on deck machinery that has culminated in an International Association of Classification Societies (IACS) review of current anchoring and towing guidelines.
'Nordic' will perform duties including rescue and recovery of damaged vessels in the North Sea. The 27-metre vessel has two specially designed Hatlapa towing winches, one behind the other, each with up to 250 tonnes dynamic pull and up to 380 tonnes static break holding force. Each winch has its own drive so it can be operated separately, and the worst-case-scenario design of the systems means 'Nordic' can recover any type of vessel, including the largest cargo ships and oil tankers, in rough weather.
Another worst-case-scenario design was developed by Markey Machinery for the tug 'Monterrey', which operates as a tethered open-sea escort for large LNG carriers in the Mexico region. The tug needed a specially designed, asymmetrical render/recover winch drive system to keep the power demand of the equipment manageable when operating in rough seas. The drives work electrically for the recovery of the line but then power need is reduced during rendering of the line by using water-cooled slip brakes.
These custom designs demonstrate a growing need for workboats able to handle the latest, largest commercial vessels under hostile conditions, and increasing vessel size is one of the reasons why IACS is currently reviewing deck machinery rules. The association has formed a project team and is also participating in a joint working group on anchoring, towing and mooring systems. Both are chaired by Adrian Kahl, a hull and anchor equipment specialist at classification society Germanischer Lloyd.
According to Kahl, the recommended breaking load of mooring and towing lines is under review in view of increasing ship sizes and changing operation needs because they must be considered in the design of shipboard mooring and towing fittings. However, the IACS review is not limited to this. Mooring rules are also under review as an increasing number of vessels are required to anchor in unsheltered and deeper waters at busy ports. Current regulations (Unified Rules A1 and A2) for the design of anchoring equipment cover mooring in sheltered waters and specify a maximum of 60m water depth but this can now be exceeded in busy ports.
"Damage to windlass motors is an example of incidents caused by the use of installed equipment under conditions for which it is not designed," says Mr Kahl.
In response to the issue, classification society ABS released a deep-water anchoring guide for oil tankers and bulk carriers this year that provides criteria for obtaining an optional class notation. The guide has requirements detailing anchor size, chain length and size, and other considerations for withstanding the environmental conditions outside a harbour area.
Aker Solutions, a member of the joint working group, is undertaking an industry education program and the company has additionally published a pocket guide to help ship's crew to understand the design limitations of deck machinery and to avoid incorrect operation. The company has also developed the Pusnes safe chainstop, a ratchet-type chain stopper that can arrest a rendering chain, preventing chain loss and protecting the windlass during anchoring operations.
Other members of the joint working group include the International Chamber of Shipping, OCIMF, Intertanko, Intercargo, the International Association of Ports and Harbors, Nautical Institute, International Marine Purchasers Association, International Tugboat Association and the International Standards Organisation. A questionnaire has been provided to the members to gather information on current operational practices and any observed damage.
It is estimated that one percent of the commercial fleet lose anchors each year but, as yet, no timeline is confirmed for delivery of the outcomes of the reviews.
Wendy Laursen
