Two RAstar 3800 Tugs from Robert Allan

Monday, January 18, 2010
Photo courtesy Robert Allan Ltd.

The Rawasi and Morooj, a pair of RAstar 3800 Class high performance terminal/escort tugs, have just entered service with their Owner, Bakri Navigation Co. Ltd. of Jeddah, Saudi Arabia.  Both tugs were built by NGV Tech Sdn. Bhd. in Malaysia.  The Rawasi was delivered to the Gulf region in late October 2009, and the Morooj in January 2010.

The RAstar family of tug designs represents a truly unique and significant development in offshore tug design.  The hull form incorporates a significant outward flare (or sponson) on the upper hull sides.  This concept was developed by and is unique to tugs designed by Robert Allan Ltd.  When the tug is heeled over under influence of the towline during an escort operation, the "weather" sponson is submerged and a large righting force is generated to improve the stability, thus increasing the towline force.  In addition, the hull has a large foil-shaped skeg, also designed to provide increased indirect forces.  This design approach is far superior to simply making a tug "fatter" on the waterline, and results in better fuel economy in all aspects of operation.

The RAstar hull form also provides dramatic reductions in roll amplitude and roll accelerations compared to old-style, wall-sided hull forms, and thus provides a much safer and more comfortable platform for the crew.  This type of performance was one of the stated objectives of the international SAFETUG JIP in which Robert Allan Ltd. are an active participant, and the RAstar hull form demonstrates superior performance to any concepts evaluated during that project.  Extensive private model tests indicate that the roll accelerations of a RAstar hull are about 60% lower than in a typical hull form of the same overall dimensions and displacement.

These tugs are equipped for typical tanker support, ship-handling and escort work, with a Plimsoll model PC-HATW/GDDG-26-10/130 double-drum hawser winch on the fore deck, with a capacity on each drum for 100 metres of 88mm diameter nylon towline.  The aft deck is equipped with a Plimsoll model PC-HTW/SD-65/150 aft towing winch, with a capacity for 300 metres of 138mm diameter nylon towline.

The accommodation is to a very high standard for a crew of up to sixteen persons.  The spacious Officer's cabins are located on the upper deck, each with private en-suite facilities.  Two additional Owners' and Officers' cabins are located on the main deck, and below decks are four more crew cabins, all served by common lavatory facilities.  The fully equipped galley serves a large common lounge/mess area on the main deck.

In common with the majority of Robert Allan Ltd. designed tugs, a great deal of attention was paid throughout the design process to mitigate the propagation of noise and vibration.  This includes the essential resilient mounting of the main engines, isolation of all exhaust system components, and the extensive use of visco-elastic floating floor systems throughout.  The shipyard executed all these requirements well, and the reward was an extremely quiet ship throughout, as attested to by the very low noise level results recorded at full power.

The wheelhouse is designed to provide maximum all-round visibility from a single split type master console.

The Rawasi and Morooj were built in accordance with Bureau Veritas Class notation:

BV 1 X Hull, X Mach, Tug, FIRE FIGHTING SHIP 1 with WATER SPRAY, Unrestricted Service
 
The propulsion machinery consists of a pair of Caterpillar model 3606 diesel engines, each rated 2,030 kW at 1,000 rpm.  These each drive an HRP model 8611 Z-drive unit with a 2,600mm diameter fixed pitch propeller.

The Fi-Fi 1 Fire-fighting capability is provided by a pair of main-engine driven pumps, each rated 1,365 cu.m per hour, which serve a pair of Hamworthy monitors and a self-protection water spray system.

Auxiliary power is provided by a trio of Volvo diesel gen-sets, each rated 250 ekW.

The principal particulars of the RAstar 3800 Class tugs are as follows:
Length, o.a.    124.6 ft
Beam, moulded    47.5 ft
Depth, moulded    20.6 ft
Maximum operating draft    16.7 ft

Capacities are as follows:
Fuel oil    46,759 gal
Potable water    45,966 gal
Lube oil    528 gal

On trials, the Rawasi and Morooj met all performance expectations, with the following results:
Bollard pull, ahead    68 tonnes
Bollard pull, astern    67 tonnes
Free running speed, ahead    13.3 knots at 100% MCR

(www.ral.ca)

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