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2 Organi di trasmissione - maggio 2011
CASE-HISTORY
Customized solutions
for Gyrofin Stabilizer System
Ciprian Radu
RKB Bearing Industries – Advanced Software
Engineering Unit
“Gyrofin Stabilizer System”
is a special project developed
by RKB Bearing Industries in
cooperation with a prestigious
European shipbuilding
corporation. The main scope of
this project was to design some
customized roller bearings to be
used for a stabilizer fin system
of a maritime ship. The ideal
solution has been found by
RKB Technical Team Unit in two
big size Application Optimized
spherical roller Bearings (AOB)
with inner bores up to 950 mm,
for support of both sides of
the fin shaft. Our engineering
solution is supported by
design process, which involves
MTDS (Main Technical Data
Sheet) calculations, 2D-3D
CAD, and FEM analysis, and
manufacturing technology,
which means high quality
materials and sophisticated
machining processes.
The operating economics of
a cargo or cruise ship are
affected by the motions
and forces due to rolling,
which can cause ship damage
and discomfort to the
crew and passengers. To solve these problems
a variety of roll stabilization systems
has been developed [7]. Anti-rolling tanks
and fin stabilizers are typical examples of
roll stabilizing devices. Of all stabilization
systems, the fin stabilizer is most effective
when a ship has relatively high speed, due
to its active control [9]. Fin stabilizers are
widely used for cargo and cruise ships requiring
high seakeeping performance in
waves. The fin stabilizer system is a hull
stability equipment used for reduction of
ship rolling up to 90% by using the generating
lift of the fins extended to both sides
of a ship [4; 6].
Active control stabilizer fins are usually
mounted on rotatable stocks at the turn of
the bilge near the middle of the ship. The
fin angle of incidence is continually adjusted
by a control system (gyroscope) that is
sensitive to the rolling motion of the ship.
The stabilizer system that uses a gyroscope,
as a control unit, is called gyrofin stabilizer
system [5; 2]. The gyrofin stabilizer develops
lift forces that generate roll moments about
ship’s center of gravity. In this way, the roll
moments are arranged to oppose the moment
applied by the waves and the roll motion
is reduced [7].
Usually, at speeds above 10-15 knots, stabilizer
fins are the most effective solution to
stabilize a ship. However, since fins usually
are not designed for ships operating at low
speed, their effectiveness decreases as ship
speed reduces [7; 3].
Retractable fins are often specified for cargo
and cruise ships. The active fins can be withdrawn
into the hull when the ship operates
in calm weather conditions to eliminate their
small resistance with the water (figure 1) [5].
Technical specifications for
gyrofin stabilizer system
Gyrofin stabilizer system is designed as a
complete system consisting of a hydraulic
driven fin, fin drive unit, electro-hydraulic
power unit, electric power controls and gyroscope
control unit (figure 2) [6].
Gyrofin stabilizer is an active system designed
to reduce the rolling when the ship
is in the water. Every ship has two stabilizer
fin systems, one for port side and one for
starboard side [10]. The arrangement being
such that, the gyroscope senses the ship rolling
movement and commands the electrohydraulic
power unit to correct that movement
by inclining the fins to the oncoming
flow by fin drive unit, and a net upward lift
force is developed on the descending side
of the ship.
The fin drive unit contains the shafting,
bearings, seals, drive components locking
device and all other mechanisms and components
to produce the driving forces and
Fig. 1 - Retractable gyrofin.
9 ottobre 2010
