In common with most Damen products the ASD 3211 has been steadily refined, with minor but significant changes made in the light of operational experience.

As a result this most recent series of vessels has a bollard pull 10 tons greater than the first tugs delivered in 1996.

All three vessels are owned by BP Shipping Ltd and registered in the Isle of Man and managed by Scottish company Targe Towing Ltd of Montrose. The latter are responsible for manning and efficient operation of the fleet. In operational terms the tugs are virtually self sufficient, with highly qualified crews capable of carrying out all of the day to day operational, administrative and maintenance tasks. Targe Towing have been responsible for the tugs and towage operations at the BP Hound Point oil terminal since BP first put their own tugs in place in 1993.

The tugs meet the requirements of Lloyds class; +100 A1 Escort Tug +LMC UMS Fire Fighting 1 with water spray. The hull design is optimised for a good stern first and indirect towing performance and incorporates a long box keel, a heavily fendered bow and an open stern. Particular attention has been given to the cylindrical fendering on the forward 'shoulders', a feature essential in tugs working alongside large ships in the 'push-pull' mode.

Another area to receive considerable thought was the fire fighting system on all three tugs. Additional pumping capacity was specified by BP to ensure that the vessels could, if necessary, support on shore fire fighting operations, with the result that the capacity aboard each vessel actually exceeds the requirements of FiFi 1.

Each vessel is 32.22m in length overall, with a beam of 11.24m and draft (aft) of 5.50m.

The all welded hull structure includes fully enclosed bulwarks, increasing stiffness considerably and reducing maintenance costs.

A large clear after deck, fitted only with a crane, bitts and tow hook, affords a good working area for the deployment of booms, hoses or other pollution control activities. Internal tanks can accommodate 171m 3of fuel oil, 56.8cm 3of fresh water, 48.3m 3of water ballast and 24.1m 3of foam compound.

Other, smaller, dedicated tanks are provided for lubricating oil, hydraulic oil, sewage, sludge and dirty oil.

Castle Point , and its sisters, are each powered by two MAK 6M25 main engines running at 750rpm (MCR) to produce a total of 5,310bhp. Power is transmitted to a pair of Rolls-Royce Aquamaster US255CP propulsion units.

The latter incorporate 2,700mm diameter controllable pitch propellers, obviating the need for slipping clutches and giving the tugmaster precise control of thrust from each unit. On trials the tugs achieved a bollard pull ahead of 66.7 tons, 64 tons pulling astern, and an almost equal free running speed ahead and astern of approximately 14 knots.

Electrical power is supplied by two Caterpillar 3304B T diesels driving 106kVA alternators and a 60kVA harbour set powered by a Caterpillar 3304B NA engine. Aboard Corringham , an experimental array of solar panels has been positioned around the slopping upper surfaces of the superstructure and is designed to automatically recharge the 24 volt emergency systems, a particularly useful feature if the vessel is on standby.

The electrical switchboards and a Praxis alarm and monitoring system are located in a small soundproof control room located forward of the engineroom.

Norgear - Kumera step-up gearboxes mounted on the front end of each main engine drive the main fire pumps and hydraulic pumps for the deck machinery.

Towing gear comprises a heavy duty split drum towing winch from DMT (a Damen product) on the foredeck and a Mampaey 100 ton quick release tow hook aft. The hydraulically powered towing winch is combined with an anchor windlass, for the two 495kg 'high holding power' anchors, and has a brake holding capacity of 175 tons and maximum line pull of 82.5 tons at 6m/min. One drum is equipped with a Marlow Superline/Steelite HMPE towline of 56mm diameter and 200m in length for general shiphandling operations and the other a 68mm diameter towline of the same material and length for escort operations. The former has a maximum breaking strain of 228 tonnes and the latter 343 tonnes. The winch is controlled from the wheelhouse and in the escort mode can maintain a pre-set towline length and tension.

Other deck equipment includes two 1 ton capstans by North Sea Winches and a Palfinger 48000 ME hydraulic deck crane. The crane is located in the portside, adjacent to the towing bitts and hook, giving good coverage of the after deck.

Also available on the crane is a winch and lifting wire attachment with a safe working load of 2 tons.

The fire fighting and self protection dousing system is supplied by a pair of Nijhuis HGT fire pumps, each with a capacity of 1,850m 3/hour at 13.4 bar, coupled to the main engines as previously mentioned.

Two remotely controlled Skum water/foam monitors rated at 1,200m 3/hour are mounted on a platform between the exhaust uptakes. The entire output from the fire pumps is distributed to the monitors etc via a massive fire main, one end of which emerges from the after end of the superstructure just forward of the towing bitts and terminates in a large bolted flange. This provides the connection point for an optional distribution manifold (carried on each tug) that can be readily put in place to facilitate a large number of standard fire hose connections.

The wheelhouse configuration follows that now familiar Damen style for this type of vessel, with full length windows giving excellent vision from the single control position, including overhead and down to deck level.

Propulsion, engine and winch controls are well laid out on consoles on either side of the 'captain's' chair. Other instrumentation is situated on overhead consoles and on a vertical panel on the portside.

Navigational equipment includes two Furuno FR-1505 Mk III radars, a Furuno GP-90 GPS system, and a Furuno FE-700 echo sounder. The magnetic compass is a Kotter type supplied by Cassens & Plath, the Gyro Compass is a Litton Navigat X Mk 1 and the autopilot a Plath Navipilot V. Communications equipment is fitted to GMDSS Area 2 standards and comprises one Sailor Compact VHF RT 4822 set with DSC and two C 4900 sets; and a Furuno package including an FS-1570 single sideband radio, NX-500 Navtex and FA-100 ASI system.

Fully air conditioned and heated accommodation is configured for a maximum of up to seven persons in four cabins.

Under normal circumstances a crew of three will operate each tug, increasing to four or more depending on operational requirements. Single cabins are available for the master, chief engineer and one officer and a further cabin is equipped to accommodate up to four further persons. A well equipped ship's office is located below the bridge deck, adjacent to the Captain's cabin. The usual galley, mess room, storage, changing room and sanitary facilities are provided, with living spaces fitted out to a high standard of comfort for crews residing in a relatively remote and isolated location.