Rimorchiatori Napoli gets the first big Compact RAstar 2700 – by Jack Gaston

As originators of the ‘Compact Tug’ concept and developers of the high performance RAstar hull form, designers Robert Allan Ltd of Vancouver in Canada were stimulated by the owner’s demands to take the logical step of combining the two. A tug was required with a high shiphandling and escort performance but with a length of less than 28m for regulatory reasons.

Cheradi is the first in a series of four tugs ordered by Rimorchiatori Napoli from the San Marco Shipyard of La Spezia in Italy. The new tugs are classed for both harbour and coastal duties and will be used in the various Italian coastal ports served by the company. All four vessels will be virtually identical and comply with RINA Class notation C +Hull, +Mach, Tug, Salvage Tug, Escort Tug, Fi-Fi 1, Water Spray, Oil Recovery Ship, +AUT-UMS, Unrestricted Navigation.

Although the term big ‘Compact’ may seem a conflict in terms, a quick look at the dimensions of this new tug brings home its significance. The tugs have an overall length of just 26.90m, with a moulded beam of 13.25m, a depth (moulded) of 5.00m and a maximum operating draft of 4.85m. Integral tanks can accommodate 108 cu/m of fuel and 11cu/m of drinking water.

A pair of Wartsila 6L26A2 diesel main engines generate a total of 4,080kW (approximately 5,544bhp) running at 1,000rpm to power Lips model CS250-S/WN-K fully azimuthing propulsion units. The latter incorporate 2,600mm diameter propellers. On trials conducted in late December 2009, this combination delivered a bollard pull of 76.1 tons towing ahead and 70.7 tons astern and a free running speed of 13.5 knots.

That level of performance was previously assured by extensive model testing undertaken at the Vienna Model Basin under the direction of Offshore Research Ltd of Vancouver on behalf of Robert Allan Ltd. Although model testing of tug designs is rare in this size range due to the size and power of this tug, and the requirement to achieve maximum escort capability, it was considered beneficial to conduct the tests and thus satisfy the shipyards’ concerns regarding performance guarantees.

In common with all the RAstar series, this new tug is expected to far outperform its typical ‘wall-sided’ competition, offering a far superior escort towing performance and reducing roll motions by at least 50%. Model testing predicts indirect steering forces in excess of 100 tons at 10 knots for this design. The RAstar hull form is also far more energy efficient, as the reduced waterline beam reduces free running resistance considerably in comparison to old style tugs of similar overall proportions.

The main towing winch on the foredeck is a double drum, hydraulic winch supplied by Romagnoli of Italy. A 70 tons capacity tow hook is mounted on a radial arm, located on the after deck for harbour towage. An obligatory anchor is stowed aft, out of the way of the main working deck forward.

Electrical power is supplied by a trio of Volvo diesel powered auxiliary generators, two of 160 kW and one harbour set of 90 kW.

Cheradi is equipped for fire fighting to Fi-Fi 1 standard. The fire pumps are driven from the front end of the main engines via Kumera step-up gearboxes, which also drive the main hydraulic pumps supplying power to the winch.

The RAstar 2700 Class tugs are outfitted for a crew of up to six persons in modern and well equipped accommodation, all above the main deck.