By Jack Gaston

The arrival of the tug SD Reliable at Portsmouth Naval base at the end of November represents a significant milestone in the contract between Damen Shipyards and Serco Marine Services for the delivery of 29 new vessels. SD Reliable is the first of four purpose built tractor tugs designed by Damen specifically to assist the largest and most modern warships likely to be used by the Royal Navy in the foreseeable future. The delivery, made two years after this major contract was signed, also marks the completion of 17 vessels - delivered on time and to budget.  

The contact was signed in December 2007 between Serco Marine Services Ltd and the Damen Shipyards Group covering the development and delivery of a 29 vessel package valued at Euro146 million. The Damen package comprised vessels of 15 different designs, including pilot boats, tugs, barges, multipurpose work vessels, a fast crew boat and a worldwide support ship. Within that total, are16 tugs and tug/workboats, some selected from Damen’s standard range and others modified or purpose designed. Three distinct Damen project areas are involved and eleven production centres within the Group, with the Tugs & Workboats project office taking the lead for a large share of the work. 

Included in the list of 17 vessels already completed are; pilot launches, workboats, multi-purpose work vessels and tugs. Most have been constructed to standard Damen designs but customised to meet the specific needs of Serco Marine Services and their support contract with the Royal Navy at HM Naval Bases in Portsmouth, Devonport and the Clyde. 

SD Reliable was built to a new design ‘tailor made’ to provide assistance to warships and other vessels where exceptional manoeuvrability, precise control and adequate power are essential. Included in the design are a number of special features required specifically for use in the UK naval bases.  Construction of the hull and all major steel work for this vessel, and its three sisterships, was undertaken by a Damen subsidiary in Poland. Once launched and prepared for sea the hulls were towed to the Maaskant Shipyard at Stellendam in the Netherlands to be fitted out to a very high standard, commissioned, and trialled prior to delivery. 

All four vessels are built to comply with the requirements of Lloyds Register of Shipping  +100 A1 Tug, Specified Coastal Service, (+)LMC, UMS and UK MCA Class IX.

SD Reliable measures 29.13m in length overall, with a maximum beam of 9.98m, depth (at sides) of 4.00m and the relatively shallow draft (aft) of 4.41m. The specially developed, single chine, hull form incorporates a large skeg aft, and propulsion units mounted well forward of amidships and protected by a small ‘docking’ skeg. An important characteristic of the chosen hull design is to ensure the tug handles and performs equally well, whether moving ahead or astern. 

Careful thought has been given to fendering. A substantial tubular stern fender provides protection while operating in the push-pull mode, and a heavy ‘D’ section moulding is used around the bow and sides. Fendering is also installed below the waterline, on the after end of the skeg and on the chines to afford protection whilst operating in close proximity with submarines. All exposed fendering is made up of mouldings manufactured using ‘grey’ coloured material, to avoid leaving unsightly marks on the grey paintwork of naval ships.  

An elongated elliptical ‘plan-view’ at deck level allows the tug to work efficiently while alongside other vessels, a mode of operation often adopted in naval dockyards. The decks have been kept as clear as possible to assist safe operation and the superstructure and wheelhouse are located amidships to afford maximum overhead clearance fore and aft. This and the location of exhaust uptakes on either side of the wheelhouse, also gives excellent all round visibility from the single control position. Bulwarks are of equal height all round the vessel, with the stern section ‘double skinned’ and the mooring bits neatly built-in to increase strength and reduce maintenance.

SD Reliable is equipped with a hydraulically driven Kraaijveld, double drum, towing winch aft. The drums can be operated independently and have a maximum brake holding capacity of 100 tonnes and a maximum line pull of 10 tonnes at 30m/min. Each drum carries 200m of 40mm diameter high performance synthetic towline. The towlines are deployed through a towing fairlead with two identical polished apertures.

A Heila HLM-20-25 hydraulically operated deck crane, with a maximum capacity of 2.2 tonnes is mounted on a pedestal adjacent to the towing winch. The crane is fitted with a telescopic jib and a Heila MW14 winch and wire attachment, considerably enhancing its versatility.

A Mampaey quick release tow hook, with a 45 tonnes safe working load, for secondary and emergency use, is mounted at the base of the crane pedestal.

The tug is equipped with a single 225kg Pool style High Holding power anchor stowed in a pocket beneath the starboard bow. A Kraaijveld windlass, provided to handle the anchor, is combined with a single rope drum with a maximum brake load of 20 tonnes and a line pull of 4 tonnes at 10m/min. This drum is used to deploy an additional line from the bow when making fast alongside another vessel.

SD Reliable and its sister ships are each powered by two Caterpillar 3512B TA HD+/C diesel main engines rated at 3000bkW at 1600 rev/min, a total of 4023 bhp. The engines are coupled via a lengthy shaft line to a pair of Rolls Royce US 205 CP fully azimuthing propulsion units. The latter incorporate controllable pitch propellers of 2150mm diameter. Flexibly mounted main engines and flexible couplings in the drive-line serve to reduce noise and vibration levels considerably.

Extensive trials with this first vessel demonstrated conclusively the ability of the tug to operate effectively in either direction. A bollard pull of 42.5 tonnes was achieved pulling ahead and 42.7 tonnes astern. The results from speed trials reported a maximum speed ahead of 13.1 knots and 13.3 knots astern.

The main engines are cooled via ‘box coolers’ and pumps coupled to the front end of each engine supply hydraulic power for the deck machinery.

Electrical power is supplied by two Caterpillar C4.4 TA auxiliary generator sets, located in the engineroom, supplying 123kVA at 400V – 60 Hz. The associated switchboards are located in an annexe to the engineroom access. Main engine and propulsion system are protected by a Praxis Maxiguard alarm and monitoring system giving indications of major faults at display panels in the engineroom, and wheelhouse.

Also located at the after end of the engineroom, adjacent to the auxiliary generators, is the 600cu/m/hr fire pump, driven by a Caterpillar 3406CT diesel. The pump supplies water to a manually operated monitor mounted aft of the wheelhouse at the bridge deck level. The monitor is suitable for fire fighting, carrying out boundary cooling and other safety related functions.

All accommodation aboard SD Reliable is located at main deck level. Provision is made to accommodate six persons in two single and two double berth cabins. Facilities include a well-fitted galley, a spacious mess room capable of seating 12 persons, dry and frozen goods stores and sanitary spaces. Durable modern insulated linings are used throughout and Dampa acoustic ceiling materials and Bolidt floating floors have been installed in the wheelhouse.

The wheelhouse is of typical Damen design with good visibility and a single control position. A  ‘Captain’s’ chair, mounted on a central track, enables the tugmaster to operate the controls while facing in either direction. SD Reliable can operate as a true ‘double ended’ vessel, with a dual lighting system that allows appropriate mandatory navigation lights to be selected according to the direction of travel.

A navigational and communications package has been selected to enable the tug to operate effectively in its designated roles. These include an Alpha Seapilot automatic pilot, two JRC JMA-5210-4 radar sets, a Kotter magnetic compass, a JRC JLR 30 GPS compass, a JRC J_NAV 500 GPS and Seiwa Explorer Echosounder and Chart plotter. Sailor VHF radios include an RT5022 set with DSC and an RT2048. Two GMDSS approved handheld VHF portable radios are also included.

SD Reliable, and sister ships SD Bountiful, SD Resourceful, and SD Dependable, have all the ingredients necessary in a versatile, highly manoeuvrable tug designed specifically to serve ships of the Royal Navy. SD Bountiful will be delivered in April 2010, followed by SD Resourceful in May and SD Dependable in July.

At much the same time Damen have been completing the first of two azimuthing stern drive (ASD) tugs to SD Marine Services. These were built to the Damen ASD 2509 standard design of 25m shiphandling and coastal tugs. The first, named SD Independent, was delivered to Portsmouth Naval base in October of this year and is the first vessel in the ‘package’ to have an ASD (stern-drive) propulsion system. This vessel and its sister ship SD Indulgent, due to be delivered early in 2010, is being used to provide essential training for masters and crews in the use and advantages of this type of omni-directional drive.

Copyright – Maritime Journal – December 2009