HANSA 03-2018

Schiffstechnik | Ship Technology
No seawater ballast – no barriers
Later this year, Hyundai Mipo Dockyard is scheduled to deliver a highly innovative
LNG bunkering vessel ordered by Bernhard Schulte Shipmanagement (BSM). The design
rises to challenges of today and tomorrow, writes Felix Selzer
The 7,600 m³ gas supply vessel (GSV)
was ordered in late 2016 and is currently
under construction with Lloyd’s
Register (LR) class at HMD’s Ulsan site.
»The project started as a TEN-T project
as part of the EU’s LNG Masterplan in
2012 to get LNG into the Rhine-Main-
Danube waterway. We applied for one
part of the program that was to supply
LNG into Constanta in the Black Sea and
to get it into the Danube where it would
then be transhipped as far as Vienna,«
John Eltringham, Project Director at
BSM, explains to HANSA.
To win the competition and get funding
for a bunker and feeder vessel, BSM
had to be very novel and innovative in
every aspect of the ship. One of the many
criteria was that the hull shape had to be
suitable for rivers and canals including a
very efficient bow and stern with reduced
wake.
The canal system posed also dimensional
constraints. BSM needed 6,000m3 of
LNG to make the ship viable and the design
had to be very much like a standard
ethylene carrier with type C tanks and aft
accommodation. To get the forward view
in line with SOLAS requirements, the accommodation
was put in the front. »Our
designers BMT Titron suggested that we
looked at a traditional supply boat design
with accommodation in front but to use
a diesel electric propulsion system. If we
used that we would have more benefits:
With forward accommodation, forward
engines, stern azimuthing thrusters and
type C tanks midships, we could balance
the ship much better and get the center
of gravity much closer to the center of
buoyancy. So we get away without seawater
ballast,« Eltringham describes the development
process.
With the entry into force of IMO’s Ballast
Water Management Convention in
September 2017, ships constructed on or
after this date are required to be fitted
with a ballast water treatment system at
delivery. The new GSV cleverly circumvents
this requirement. The ship will
only have a little quantity of fresh water
on board which is only used for trim
purposes and does not leave the ship. The
concept from BMT Titron was taken over
by HMD and developed further into a
mature design.
The shipyard extended the beam and
increased the permanent ballast by a few
hundred tons. The difference in draft is
2.25 m from fully laden to ballast, the hull
draft including cargo is only 2.85 m. »That
is the good thing about LNG, it is not the
heaviest cargo. The design just lends itself
to the seawater ballast free concept,«
Eltringham explains. HMD also had to
address speed management by deadrise.
Dead-rise is known to help improve
the ship’s stability, which is critical to a
»ballast-free« vessel, but it is also likely
to deteriorate its speed performance. To
counteract this, HMD developed a better
performing dead-rise hull shape, tested
through wet model tests.
The gas process is the key
Another key feature that enables the seawater
ballast-free concept is the twin
propulsion system with two azimuth
thrusters. The smaller propeller diameter
enables the vessel to achieve full immersion
in all operational conditions.
»Some of our innovation was just too innovative,«
Eltringham says. »We wanted to
use lightweight covering almost like modern
high-rise building cladding, which is
airtight and structurally very strong. But
that was a step too far for HMD, so we
went back to a traditional steel canopy
deck. We are still under 1,000 t in a maximum
condition of ballast – without seawater,
which is great, because now we don’t
need a ballast water treatment system.«
The designers have also been innovative
on the gas process, the power station
arrangement and the transfer and other
Source: BSM
64 HANSA International Maritime Journal – 155. Jahrgang – 2018 – Nr. 3