A second pair RT Discovery and
RT Endeavour were delivered by the Cheoy Lee Shipyards in Hong Kong, to the
same owners for use by Kotug and their joint venture partners in Port Hedland, Western
Australia. These two vessels represent the first part of four-tug order placed with
Cheoy Lee, with the prospect of further additions in the near future. This batch
are virtually identical to the Hybrid version, described in this feature, but have
diesel propulsion systems, slight differences deck machinery, and are equipped
The ART 80-32 was designed by naval
architects and consultants Robert Allan Ltd (RAL) of Vancouver with significant
input from Kotug and Rotortug BV reflecting some 25 years of consolidated
operational experience. After previously working together on several design
projects an agreement between Rotortug BV and RAL was signed in 2012 which made
Robert Allan the exclusive designer of all Rotortugs worldwide. Likewise Damen
Shipyards and Cheoy Lee Shipbuilders were given the right to build and market
Rotortugs as part of their own sales portfolios.
The hullform for the ART 80-32
incorporates many features developed by RAL for high performance escort tugs and
adapted to suit the Rotortug concept to provide enhanced stability, sea-keeping
and escort performance. The design process involved a detailed Computational
Fluid Dynamic (CFD) study of different hull forms to determine the preferred
hull characteristics. After considerable research the resulting double chine hull
incorporates a pronounced sheer, a semi-raised foredeck, small bilge keels and
sponsons to minimise the possibility of ‘deck-edge immersion' during escort operations. At the same time it was essential to retain
and enhance the Rotortug’s unique omni-directional manoeuvrability and
Design and construction of the
new ART 80-32 series meets the class requirements of Lloyds Register of
Shipping with the following notation:+100 Tug+ LMC,UMS,IWS. They are vessels of
491gross tons, measuring 31.95m in length overall, with a beam of 12.60m and a
maximum draft of 6.93m.
On trials all four tugs
achieved bollard pull figure exceeding the specified 80 tonnes pulling in
either direction along with a free running speed of 13.5 knots sailing ahead and
astern. The agility of this new breed is spectacular, manoeuvrability and
station keeping are quick and precise,
along with side stepping capability to port and starboard at 7.5 knots.
When RT Evolution, the first
Hybrid version of the ART 80-32, arrived in its home port of Rotterdam it
caused considerable interest. Your MJ correspondent is grateful to Kotug and
Rotortug BV for the privilege of visiting and taking a trip on the new vessel.
At first sight RT
Evolution is of a spacious and clean design an impression that prevails
throughout the vessel. The decks and full height bulwarks have been kept as
free as possible from unnecessary obstructions and the inherent sheer of the
hull is plain to see. Shiphandling fenders at the bow comprise an
upper row of 800 mm diameter cylindrical rubber moulding with a lower course of
‘W’ section moulded rubber blocks. The stern is protected in the same way and
the sheer lines have two rows of ‘D’section
300 mm x 300 mm lightweight Polymarine foam moulding.
A single drum, electrically
driven towing winch, manufactured by DMT, is installed fore and aft. The
forward winch incorporates a windlass for the vessel’s single anchor. The drums
on both winches have a brake holding capacity of 230 tonnes and accommodate a
230m towline of 80mm diameter ‘Ultra-line’, with a 20m forerunner (pennant) of
64mm diameter Dyneema connected by means
of a Kotug patented ‘ ‘Ko-link’. The towline from each winch is deployed via an
‘A’ configuration tubular towing staple lined with stainless steel. The precise
positioning of the staple on the deck forward and aft is critical in order to
provide a safe and effective tow-point.
A spacious engineroom houses
all three main engines, two auxiliaries and most of the necessary ancillary
equipment. Each of the "C" rated, IMO Tier II Compliant, Caterpillar 3512C HD main engines is rated
at 1765 kW (2365bhp) running at 1800 rev/min. Power is transmitted from each
main engine to a Schottel SRP 3000 fully azimuthing thruster with a 2.3m
diameter fixed pitch propeller, via a Twin-Disc MCD 3000 LD slipping clutch. Also located in each shaft-line is a
Westinghouse-Teco 500kW motor/generator.
The Schottel azimuthing
thrusters, two forward and one aft, are located in separate compartments
separated from the engineroom by transverse bulkheads and watertight doors.
Each unit is fitted with frequency controlled electric steering motors designed
to achieve the required response time of one 360 degree rotation in 16 seconds.
RT Evolution has two auxiliary
generators of different capacities. A Caterpillar C18 diesel driven generator
of 450ekW provides current for the Hybrid propulsion system and winches. A
smaller Caterpillar generator C9 of 200 ekW supplies the ship’s systems,
battery charging and the Hybrid system when required.
Two Corvus Lithium Polymer
battery packs are housed in a specially designed compartment adjacent to the
engine room, with its own ventilation, monitoring and alarm systems.
Access to the engine room is through
the engine control room and its adjacent switchboard room at main deck level
which to offers a degree of acoustic isolation from the crew accommodation.
The Xeropoint Hybrid power
integration system installed in RT Evolution and its sistership was devised by
the Canadian company Aspin Kemp Associates Ltd (AKA) and is a refined version
of that developed for use in Kotug’s hybrid Rotortug the RT Adriaan. The latter
was one of an earlier series of Rotortugs built in 2010 and retrofitted to
become Europe’s first true Hybrid tug in November 2011. RT Adriaan has been in
service almost continuously since its conversion and has achieved a reduction
in fuel consumption of approximately 15% and reductions of 44% Hydrocarbons,
33% NOx and 38% SOx emissions. The new ART
80-32 Hybrid Rotortug is expected to improve on those figures thanks to the
vessel’s improved hullform and hydrodynamic characteristics.
An important advantage of the Hybrid
system is to ensure that the diesel engines onboard the vessel are operating as
close as possible to their designed optimum and most efficient condition. In most
diesel driven tugs the main engines only operate at maximum power for as little
as 2% of their working lives. With a hybrid propulsion system much of the slow
speed, low load, operation is carried out using electrical power from the
batteries or from diesel generators operating close to their most efficient
condition. Among the added advantages are reduced maintenance costs due to lower
main engine running hours. Reduced noise levels in a Hybrid vessel improve
working conditions for the crew. In all Rotortugs there is greater propulsion
system redundancy thanks to the triple thruster configuration. In the Hybrid the
electric motors are also available in the event of a main engine failure.
The Hybrid propulsion system
is very simple to operate from a panel on the wheelhouse console. Two small
rotary switches on the panel, with associated indicator lights, give the
Captain complete control of the ‘hybrid’ system. One selects HYBRID or
NON-HYBRID propulsion. The other selects any one of five operating modes STOP –
IDLE – TRANSIT 1 – TRANSIT 2 – ASSIST. The ‘Xeropoint Hybrid’ colour display
screen mounted on the overhead console shows in diagrammatic form the entire
propulsion system, the active components and the flow of electrical and diesel
power. A similar display is mounted on the AKA control cabinet in the switchboard
With HYBRID selected on the switch panel and the mode selector set to STOP - No engines are running and the
vessel’s own electrical system is fed by the battery pack via the main
switchboard. When fully charged the batteries can maintain vessel services for
up to 8 hours. Once the battery capacity falls below 30% one auxiliary generator
will come on line. Alternatively if shore power is available the batteries can
be charged and the vessel systems maintained.
In the IDLE mode thrusters are powered by the motor/generators in the
shaft-line on batteries alone, enabling the tug to maintain position with a
maximum speed of 3 knots for about 1 hour.
With TRANSIT 1 selected the thrusters are powered by the
motor/generators with both auxiliaries running to give vessel speeds of up to 7
knots. The vessel systems are supplied and any surplus power is used for
With TRANSIT 2 selected the port and starboard thrusters are powered by
their electric motor/generators from the main switchboard and the centre (aft)
main engine drives the aft thruster to give a vessel speed of up to 11 knots.
The motor/generator in the aft shaft line acts as a generator and if necessary
one auxiliary will go on-line automatically.
In the ASSIST mode all thrusters are being driven by the main engines for
towage assistance and speeds of up to 13.5 knots. The motor/generators supply
the vessel services and any surplus power is used for battery charging.
The wheelhouse aboard RT
Evolution is one of the vessel’s most striking features offering exceptional
all-round visibility through full height windows. Located in the centre is one
of the first Alphatron – Alphabridge Tugboat consoles to be fitted in a vessel
of this type. Comprising two ergo dynamically designed consoles with a central
Captain’s chair mounted on rails, the consoles contain the majority of controls
and instruments required to operate the tug. At each end of both consoles is a
semi-retractable screen, one with the radar display, switchable for the river
and sea sets, and the other a multi-function screen displaying navigational and
other functions. The Captain’s chair can be turned and positioned to face in
either direction and the displays are arranged to ensure that the screen
functions are always in the same position. All of the other controls and instruments
are cleverly grouped together on purpose designed panels. An overhead console
is provided for radios and other instrumentation and includes a centrally
mounted screen showing the Xeropoint data.
RT Evolution has fully climate
controlled accommodation fitted out to a high standard for a maximum of six
persons, although in Rotterdam a crew of three is the norm. The main deckhouse contains the
entrance lobby, galley, mess, a WC and two single en-suite cabins for the
Captain and Engineer. The lower deck contains two double berth en-suite cabins,
a laundry, and galley stores.
By Jack Gaston