Ways to Conserve Energy on Board - DNV

Persistent sloshing in partly loaded LNG carrier tanks can cause extensive
damage <strong>to</strong> the tank walls. The software solution GL SeaScout helps
naviga<strong>to</strong>rs find alternative routes <strong>to</strong> avoid excessive sloshing
Pho<strong>to</strong>s: Dps.fo<strong>to</strong>@gmail.com/Romanausks/Surz01 | Dreamstime.com
In heavy seas, vessels can roll by up <strong>to</strong> 30 degrees. With
vessels getting larger and faster and crews often lacking
experience, there is a need <strong>to</strong> forecast ship behaviour
more reliably rather than leaving it up <strong>to</strong> the naviga<strong>to</strong>r <strong>to</strong>
assess the situation when he, or she, is stationed some 50
metres above the waterline. This is especially critical at night.
Vessels and their cargoes are subject <strong>to</strong> heaving, pitching,
slamming, wave loads on deck, and in certain cases, parametric
roll, which can also adversely affect deck cargoes of
containerships. Dr Torsten Büssow, GL’s Vice President Maritime
Software, explains that sloshing produces strong forces
acting against the tank wall, which could destroy or severely
damage a tank; once started, it is often even audible <strong>to</strong> the
crew. Repairs can be extensive, taking three or more weeks,
not <strong>to</strong> mention the costly offhire time. Damage induced by
sloshing could also cause loss of cargo due <strong>to</strong> gas boil-off.
“These are valuable ships and cargoes. Sloshing is a concern
for owners,” Büssow says.
Seakeeping Qualities
During the voyage of a laden LNG carrier (LNGC), the cargo
volume in the tank will gradually shrink due <strong>to</strong> gas boil-off.
This provides the cargo with increasing space <strong>to</strong> slosh in response
<strong>to</strong> the movements of the ship. Impact pressures can
be very high but of short duration, mainly affecting the tank
corners, the tank dome and internal piping.
Over the years, GL has gained considerable experience
in the study of ship seakeeping qualities. “What was lacking
in the past,” says Büssow, “was an onboard component,
such as a fleet management guide, <strong>to</strong> help naviga<strong>to</strong>rs react
appropriately <strong>to</strong> certain sea conditions: Naviga<strong>to</strong>rs need help
in judging the seakeeping behaviour of their vessels so they
can answer questions such as: If my ship swings ten degrees
<strong>to</strong> port, how will this affect its rolling motion?”
Top-Performing Software Solution
To provide a <strong>to</strong>ol for assessing gas carrier and containership
behaviour patterns, Germanischer Lloyd introduced GL
SeaScout, a hydrodynamic integrated software solution for
navigational decision support. Marketed mainly <strong>to</strong> the LNGC
sec<strong>to</strong>r, the new software applies computational fluid
Tool.
CFD-based
simulation
helps <strong>to</strong>
predict
sloshing
occurrence in
certain sea
and sailing
conditions.
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