Designed to meet growing demands for a small, compact, but powerful shiphandling tug, the ASD 2411 concept was first introduced to the towage industry in a paper presented to the International Tug and Salvage Convention in 2002. The new vessel was developed by Damen's Tug & Workboat project team, based in the Netherlands at Gorinchem, and is the result of considerable market research, calculation and tank testing.

Once the design was finalised Damen Changde was given the task of constructing the first two prototype vessels, an order later increased to four. China was originally chosen as the venue for construction in the expectation that the new vessel will meet demands for this type of tug in the Far East and Australasia.

The Changde yard has been dramatically modernised by Damen and with the company's own production and quality standards in place, the end product is a vessel built to very high standards. Among the improvements carried out in the yard are new construction and assembly halls and a sophisticated vessel transfer and slipway system. In accordance with Damen Standard production methods, also adopted by Damen Shipyards Changde, the vessels are only launched when they are 100% outfitted and finished.

Damen is also using two shipyards located in Viet Nam where ASD 2411 production is also taking place, with a similar integration of Dutch expertise and standards.

The original ASD 2411 design criteria was governed by a two-man crew requirement demanding a moulded length of less than 24m. A final moulded length of 23.95m was decided and because the tug is designed to have a bollard pull equal to the much larger ASD Tug 3111 series, a slightly larger moulded beam of 10.7m was chosen.

On deck, the layout aft is very different from any other Damen ASD tug. Because the vessel tows mainly over the bow, a spacious fore deck was considered essential and a fore deck layout identical to the ASD Tug 3111 was adopted. The new afterdeck layout was also necessary to enable standard engine room access hatches to be fitted, in keeping up with other Damen tugs. These engine room access hatches, located adjacent to the aft towing bitts or winch, must be big enough to allow the main engines to be removed or re-placed. This required additional stiffness in the deck structure and special care to achieve adequate sealing.

Although primarily intended for two-man operation, it was obvious that some clients would require more crew accommodation and to that end accommodation for a crew of up to five persons has been provided, all at main deck level. Because the deckhouse of the ASD 2411 is located further aft and directly above the engine room the main engines are, as standard, installed on resilient mountings in order to achieve the same low noise levels as the larger ASD 3111. The exhaust silencers, normally fitted below the accommodation, are in the this tug resiliently mounted on the bottom frames in the aft of the engine room.

Adsteam Ferriby is a vessel of 24.55m in length overall, with a beam of 11.49m, and a maximum draft of 5.40m, designed for operation by a small crew. The hull form incorporates several features found in other well-established Damen ASD tugs. These include a smooth, rounded, form with a heavily chamfered stern and deep box keel. An unusual design of aft skeg is an open extension of the box keel to facilitate docking supported by two struts in a 'V' configuration. This arrangement was the result of considerable study and is intended to enhance course stability without degrading the tug's ability to side-step or turn. In the early days of towage, tugs were often described as being a 'floating engineroom'.

This is certainly the impression that immediately comes to mind with this vessel. Below decks the hull has three main areas, a massive engineroom allowing a very practical layout, the Azimuthing drive compartment, and a forward compartment subdivided into an auxiliary machinery space, workshop and provision for various stores.

Dedicated tanks are allocated for 74.8m 3of fuel oil, 15.4m 3ofwater ballast, 7.5m 3of fresh water, 5.7m 3of foam compound and 4.8m 3of lubricating oil.

Two Caterpillar 3516B TA HD/D main engines provide 5,592 brake horsepower at 1,600rev/min to drive a pair of Rolls Royce US 255 propulsion units. The main engines and auxiliary machinery make use of box coolers (incorporating an anti-growth system) and a forced ventilation system rated at 60,000m 3/hour is installed.

Power is transmitted through Twin Disc MCD 3000-3 LD slipping clutches to drive the 2,600mm diameter propellers of the fully azimuthing units.

The main engines and propulsion units are widely spaced in the sizeable engineroom, with a shaft line that has been kept as straight as possible. Located between the main engines are two Caterpillar 3304B T generator sets rated at 106kVA, 50Hz, 400v, each. A further Caterpillar 3306B TA, located forward of the port main engine, powers the fire fighting pump, supplying 600m 3/hour at 10 bar to a single manually operated monitor at bridge deck level. Hydraulic power for the deck machinery is supplied by two pumps, one located on the forward end of each main engine.

On trials Adsteam Ferriby achieved a bollard pull of 70.4 tonnes ahead and 65.0 tonnes towing astern, with an almost identical free running speed of 13.2 knots ahead and 13.0 knots astern. The agility demonstrated by this tug is phenomenal and handling characteristics going astern and during shiphandling are reported to be first class.

While shiphandling the tug tows from a hydraulically driven, split drum, Kraaijeveld winch and anchor-windlass on the foredeck. The two-speed winch has a line pull of 18 tonnes at 11m/min or 9 tonnes at 22m/min, with a brake holding load of 150 tonnes. No deck machinery has been fitted aft and the only provision to tow astern is the mounting of a substantial, centrally located towing post.

Substantial fendering is fitted comprising block, 'D' section and cylindrical rubber mouldings.

Particular attention has been given to the bow and 'shoulders' where most heavy contacts take place while working in close contact with ships in the 'push-pull' mode. To reduce the likelihood of damage to the tug during operations of this kind, especially while working under the flare at the bow and stern of a ship, the exhaust uptakes are steeply angled, the superstructure chamfered and the wheelhouse configured for maximum clearance.

A well-glazed wheelhouse is typical of other vessels in the Damen range with excellent all round visibility. The tug-master has a single control position at the forward end of the wheelhouse, between the two main units of a 'slit' console.

A main Rolls Royce propulsion unit/engine speed controller is located on each side of the console in the usual way. The winch controls are also located and easily accessible on the left console.

A Simrad AP-50 auto-pilot is provided, along with a Cassens & Plath Compass, a Furnuno FR-1505 Mk III radar, GP-90 GPS and FE-700 Echosounder. Two Sailor RT 4822 VHF radios are fitted, along with a Furuno Navtex NX-500 and two Jotron TR-20 VHF hand sets.

The fully air-conditioned accommodation has provision for up to five persons in three cabins, one single for the captain, one single engineers cabin with an additional 'Pullman style' berth and a double for the crew.

A galley, mess room and the usual sanitary facilities are also incorporated. Noise levels in the accommodation and wheelhouse are further reduced by means of 'Dampa' acoustic insulated ceilings and 'Boldt' floating floors.

After the excitement of demonstrations in Rotterdam, a trouble-free delivery voyage across the North Sea and a christening ceremony in Grimsby, Adsteam Ferriby quickly took up station with the Adsteam fleet.

The tug is now part of the large Immingham fleet serving not only the enclosed dock system but also major oil, bulk cargo and vehicle carrier berths on the river Humber. In that environment Adsteam Ferriby works along side the larger Damen ASD 3111 Lady Laura in a fleet that also has several Voith tractors. Initial feedback indicates that this latest, smallest addition is proving very popular among crews and clients.