Home' Work Boat World : October 2015 Contents NAVAL ARCHITECTURE AND MARINE DESIGN
Integration of the propulsion system into a ship’s aft hullform
is not a new concept, but is paramount for a “fit for purpose”
ship design. Such integration may often stimulate debate
between two equally important and proud naval professions;
the na val architect and marine engineer. However, perso nal
prejudices aside, the importance of good integration in this
area can be the difference between a “good” ship design and an
One company offering such integration is Servogear, notably
with their Ecoflow Propulsor. Servogear works with the ship
designer and provides a tunnel to integrate in the hull with each
propeller, combined with a rudder arrangement. This not only
allows one company to take responsibility of the gear box, shaft
line, propeller and steering requirements, but they also manage the
propeller, rudder and hull hydrodynamic interaction. By doing this
Servogear take control of the hydrodynamic thrust and wake
coefficients, providing less design variables which further allows
them to optimise their propeller design.
For example, a more evenly loaded propeller in a tunnel gives a
slimmer and lighter design, which means less weight and drag as
well as a higher propulsive efficiency.
The high speed crew boat market is an area where this
concept is gaining popularity with often conflicting vessel
propulsion requirements. The Servogear Ecoflow Propulsor
concept provides an optimum combination of speed, bollard
pull, m anoeuv rability, fuel efficiency and superior vessel control
in adverse weather conditions.
Servogear’s integrated propulsion system
Designed by naval architects Robert Allan Ltd., tugs ‘Resilient’
and ‘Resolute’ were delivered to PSA Marine of Singapore by
Cheoy Lee Shipyards in 2015. They joined their existing sister
tug ‘Rubicon’, completed by the same builder in 2014.
The twin designs are 32 metres long, with a running speed of
12.5 knots and summer load draught of 4.19 metres. The main
propulsion for each tug comprises a pair of Niigata 6L28HX diesel
engines, each rated 1,654kW at 750rpm, and driving a Niigata
ZP-31B fixed pitch Z-drive unit, in ASD configuration.
The vessels can carry a crew of up to 10 people. Deck machinery
includes a forward hawser/anchor winch, aft towing winch, towing
hook, deck crane, mooring bitts at forward, midship and aft deck.
They feature an Azimuthing stern drive (ASD) for ship-assist
service and coastal towing, and are designed to operate in restricted
The lower deck contains four, two crew cabins, a double shower
stall lavatory, a galley store and main switchboard room.
Two identical diesel gen-sets, each with a power output of
112ekW, make up the electrical plant.
Ship-handling fenders at the bow comprise two rows of 800mm
by 400mm cylindrical fenders; a 480mm by 300mm “W” block
type fendering below. A 300mm by 300mm hollow “D” fender
provides protection at the main and foc’sle deck sheer lines, and
500mm by 450mm “W” block type fendering is used at the stern.
Robert Allan Ltd. designs twin tugs for PSA Marine
US dredger builder Ellicott has announced a newly designed
500mm cutter suction dredge, the Series 2070 Dragon.
This unit will eventually replace the series 1870 Dragon as
Ellicott’s standard and in-stock 500mm dredge.
Like the 1870, the 2070 Dragon supplies ample power to the
pump using a dedicated engine rated at 970kW and has a separate
328kW engine, dedicated to the hydraulic system. This dual-engine
system allows for full hydraulic power to the cutter and winches,
even when reduced RPMs on the pump are called for.
The entirely new hull was designed to meet Bureau Veritas rules
for sheltered waters. The new design criteria allows for increased
portability and easier construction in the field. Ellicott
accomplished this by reducing the number of side pontoons from
four to two. In addition the dredge uses a new, simplified bow
Another major improvement is the hydraulic system, which is
now based on highly variable displacement pumps. This approach
allows for lower energy input and thus less fuel usage to get the
same hydraulic powe r to the devices. The 2070 is also equipped
with an electric over hydraulic control system using Parker IQAN
controllers for increased reliability. Options such as anchor booms,
or spud carriage, or swivel elbow discharge can be easily added.
With its design to Bureau Veritas sheltered water rules, 500mm
discharge, five-metre digging depth, and improved portability, the
Series 2070 Dragon is suitable for a variety of projects including
harbour, river and waterway dredging, land reclamation projects,
sand mining, and mining and tailing pond assignments.
Ellicott’s new dredger design allows for increased portability
Servogear’s Ecoflow Propulsor
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