Note: Descriptions are shown in the official language in which they were submitted.
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Turret device
A turret device which is moored to the ocean floor, and a
floating structure which is supporting the turret device and
can turn around it. The turret device comprises a lower
radial plane bearing with relatively small width and large
diameter. This bearing will hold the substankial part of
the horizontal forces acting on the vessel. An upper
spherical axial bearing with relatively small diameter
sup~orts the vertical forces which are acting on the turret,
and a possible unbalance between the horizontal forces from
the mooriny line(s) and the lower bearing. A mechanism
allows rapid disconnection and reconnection ~ the turret.
Turret devices f~r mooring o~ ~hips are known amongst other5
from us-patents 3191201 and 3279404. The drawbacks and
deficiencies of known turret devices are mainly connected
with their dimensions. These turrets are large and heavy,
and this ~auses the manufacturing to be time consuming,
20 difficult and expensive. Further, the large dimensions of
the turret necessitate a correspondingly large well (cut-
out) in the hull. This well can be difficult to arrange
when modifying an existing ship, and under all circumstances
the laxge cutout represented by the well must be struc-
turally compensated by substantial rein~orcements in thewell area.
Hull deformations cause the bearing designs to be compli-
cated.
If the vessel is to be disconnected from its anchor mooring
lines, this must be done by disconnecting one anchor line at
a time. Such operation is time consuming and can be
critical in an emergency situation.
The ahove mentioned turret devices are positioned midship or
in the ~orward half of the ship.
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There are also smaller turret devices positioned in front of
the ship's bow. The connection to the ship consists of a
strong bearing housing which is transferring all the bearing
forces. This bearing housing is positioned below the water
surface. The structure which is supporting the bearing
housing must be relatively strong because of the sea forces,
which are largest in this part of the ship, and the bearing
forces which are acting in all directions. Emergency
- release of the respective mooring lines is impossible
because the lines are fixed to a plate below the bearing.
Emergency release of the comparatively strong bearing
arrangement below water is also practically impossible.
Riser tubes are conducted through the center of the bearing
and ~urther through a tubular structure up to a fluid
transferring swivel on leve~ with the forecastle deck.
.
There is also a loading buoy, NP 864496, which is clamped to
the bow of a ship with two rigid clamps of several meters
diameter, one upper and one lower. When releasing thiS
buoy, the clamps must be detached and the loading buoy with
its bearing arrangement is released from the ship.
.
The particular advantages obtained by this invention is a
simple and light weight turret with a flexible bearing
arrangement which is simple to install in the vessel, and a
coupling mechanism which makes possible a simple engagement
and release between the turret and the vessel. This
- invention comprises a turret arrangement with very limited
dimensions. It is simple to release the anchor moored part
of the turret in an emergency situation, or if the floating
structure is to be temporarily moved for transportation of
cargo, repairs or other reasons. The reconnection when the
floating structure is returned is also simple.
The essential features of this design are the bearing
arrangement and the coupling mechanism. A lower bearing
- which only takes horizontal forces, is fitted in the area
where the horizontal component of the anchor mooring forces
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are acting. Thereby it is almost only axial forces which
shall be transferred further to the upper bearing, where
also the coupling mechanism is ~itted.
However, the point of attack for the horizontal component of
the anchor mooring line force will vary slightly if there
are several mooring lines. When the horizontal component of
the mooring line force deviates from the center of the lower
bearing, there will be a moment. This moment is transferred
as a bending moment in the structure, and it is resisted by
a small horizontal force in the upper bearing.
The upper bearing is shaped like a spherical axial bearing.
Thereby it can absorb large axial forces and moderate radial
forces, at the same time as it will align itself in the
direction of the center of the lower bearing. Such flexible
alignment is important on floating structures, where defor-
mation between the various parts of the hull easily occurs.
.
The upper bearing is made with relative small diameter, and
in this way also the diameter of the coupling mechanism can
be kept small. A small diameter gives small frictional
bearing losses, at the same time as it simplifies tha design
of the coupling mechanism, and it provides ample clearance
when the top of the turret is t~ pass the lower bearing. To
obtain space for one or a few riser tubes in center of the
bearing, the diameter of the bearing mus~ be approximately 1
meter, but strength in the bearing and the coupling
mechanism can permit a smaller diameter.
The coupling mechanism is in principle a multiple thread
screw joint with a'pitch large enough to cause unscrewing
due to the axial force in the turret. The turret is not
rotating in this situation and is moving vertically
downwards with one coupling part, while the other coupling
part is suspended in, and is rotating with, the upper
bearing. In the engaged position the two coupling parts
must be secured relative to each other to prevent relative
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rotation.
The lower bearing is made as a plain bearing with substan-
tially larger diameter than the upper one, such that the
structure above can pass through the bearing with ample
clearance. A large diameter also gives the possibility of a
narrow bearing for the same surface pressure. Small width
bearings have less tendency for edge pressure when mis-
aligned, and when the anchored part of the turret is to be
released, the axial movement to clear the outer bearing
surface is small. This is important by emergency release.
The turret arrangement will consist of three main parts:
15 1) The turret,
2) ~he upper spherical axial bearing with release mechanism
and
3) the outer ring of the lower radial bearings with its
attachments to the hull.
In the lower part of the turret there is a table or a bottom
plate to whicb the anchor mooring lines are fixed. If there
is only one linej it must be fixed in the center, and in
that case it would be natural to replace the line with a
torsional rigid tubular element which is connected by a
cardan joint.
Normally, several anchor mooring lines of chain cable or
steel wire rope are used.
The bottom plate is connected to the inner ring of the lower
bearing through an intermediate structure. This inner ring
must be very rigid to maintain its roundness when the
bearing is strained. The inner ring can be compared to a
wheel with a cylindrical external surface, preferably
stainless. A tube is fixed to the center of the bottom
plate and the lower bearing, and is extending further to the
upper bearing.
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It should be possible to lock the tube ,in several positions
in order to maintain it fixed during inspection, maintenance
or adjustment of the bearings and the anchor line attach-
ment.
One or more riser pipes may be guided inside the tube and
connected above the tube to a swivel with one or several
paths.
The turret may be provided with buoyancy means where
suitable with regard to adjacent structures. It is natural
to consider the buoyancy means in connection with the anchor
lines and their pretension in such a way that the turret
maintains a stable vertical equilibrium below water when it
is disconnected.
The upper bearing shall be looked upo~ as one unit, even
though the inner ring is foll~wing the turret motions and
the outer ring is following the vessel. A sleeve has an
external collar which is suspended in the inner ring of the
bearing. This sleeve can be supplied with internal threads
like a nut, for connection to the turret, but a preferred
embodiment is to extend the sleeve downwards below the
beari~g and provide the sleeve with external t~reads in the
lower part o~ the extended portion. Thereby the exposed
upper end of the vertical tube in the turret can be provided
with internal threads which are very wel,l protected against
contact damage.
In the area between the bearing and the threaded portion the
sleeve can be provided with axial splines for guidance of a
dog clutch. The dogs may engage similar dogs in the top of
the tubular turret, and thereby lock the turret against
rotation relative to the sleeve.
Hydraulic jacks can press the dog clutch out of dog
engagement if a sudden emer~ency situation should arise.
Then the sleeve will rotate on the threads until the turret
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is free.
The threads are preferably coarse trapezoidal threads with
large width. When the turret is to be engaged, this
coupling procedure may be facilitated if the sleeve, which
is suspended in the spherical bearing, can be oriented
towards the center of the turret tube. Guide means can be
fitted on the sleeve or on the turret tube, and by contact
against the tube or the sleeve, the sleeve is oriented.
When the first threads have contact with the opposite
threads, the contact pressure can be used to align the
sleeve in such a way that all the threads get contact.
Externally the upper bearing is supported in a bearing
housing, which is resting in a bracket or the like, fixed to
one of the upper decks or to the upper part of the vessel's
bow.
The outer ring of the lower bearing can in principle be an
elastic U-shaped strap surrounding the rigid inner ring, and
with the two legs ~itted to the hull in order to take the
main load, which is longitudinal mooring load in direction
aft. The mooring load will then be evenly distributed to
the bight in the U, and further to the parallel legs and the
hull.
However, there will also be side forces, and in some cases
also longitudinal forces in direction forward. In order to
take these loads t the outer ring must be complete and have a
certain stiffness in one or two areas. For arrangement in
the bow of a ship, it is natural to make the aft half of the
outer ring rigid, while a natural arrangement in the bottom
of a ship can require the whole ring rigid.
The outer ring can also be a polygon with a bearing element
in each corner. This is a preferable embodiment because the
araa of the expensive self-lubricating bearing material can
be limited, and good access to the bearing elements may be
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had.
On deck a winch is preferably arranged for hoisting the
turret during connection and for lowering the turret during
disconnection.
The same winch or one or two other winches can be used to
tighten or slacken the anchor lines.
The Figures 1 - 6 show examples of embodiments of the
invention. The vessel can turn freely 360 degrees around
the axis of a turret 12, which axis is vertical. The
bearing arrangement of the vessel l and the turret 12
consists of an upper spherical thrust bearing 2,3 which
mainly is carrying vertical loads, and a lower bearing 4,5
which only carries radial loads. The upper spherical
bearings 2,3 and the attached coupling mechanism 31, 32 or
35, 36, have a relatively small diameter and are well
protected above the sea surface 11.
The lower bearing 4,5 is preferably a self-lubricating
sliding bearing which can operate submerged in sea water.
The inner ring 3 in the upper bearing is through the
coupling mechanism fixed to a tube 6, which is connacted ko
the inner ring 4 in the lower bearing, and ~urther to the
bottom plate 7, which is moored to the ocean floor by a
number of anchor lines 8.
The rotating part of the turret 12 further consists of a
sleeve suspended in the inner ring 3 of the upper bearing
and coupling the bearing to the tube 6, brackets 14, inner
ring 4 in the lower bearing and the bottom plate 7. The
turret 12 may also be equipped with buoyancy means 15, or
closed spaces providing buoyancy. The purpose is fully or
in part to compensate for the weight of the turret 12 and
also the vertical component o~ the tension in the anchor
lines 8. Thereby the turret 12 can obtain a stable
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equilibrium a distance below the surface 11 if it should be
decided to uncouple the turret from the ship 1 for a period.
In this case the connection between the sleeve for the inner
ring 3 and the tube 6 must first be released. When the
turret 12 is to be reconnected to the ship, the turret can
be lifted by means of a line from a winch 29 through the
bearing 2,3.
One or more riser pipes 9 can pass through the tube 6, and
the medium in the pipes can be transferred to or from the
ship by means of swivels 10. One or two winches 30 on deck
can be used to tighten or slacken the anchor lines 8.
Figure 1 shows the turret 12 arranged in the ~ow of a ship
1. The outer ring 2 in the upper bearing rests in a bearing
housing 38 on the deck 16 above a tubular shaft 2Z surround-
ing a cutout in the flared bow. The sleeve 35 is suspended
in the inner ring 3 of the spherical bearing and is engaged
through a multiple thread connec~ion with a hub 37, which is
welded to thP top of the tube 6. A dog clutch 36 can slide
axially on the sleeve 35 and lock it for rotation xelative
to the hub 37. These details of the spherical bearing and
the coupling mechanism are shown in more detail on Figure 5.
The horizontal plate 23 participates in thQ connection of
tha outer rin~ 5 to the hull 1. Ins~de the hull plating a
plate is shown dotted in line with the plate 23. ~he
brackets 14, which also may be a full con~, can guide the
inner ring 4 into the outer ring 5 during connection o~ the
turret 12.
Figure 2 shows a horizontal section at the lower bearing
4,5. The inner ring 4 should be relatively rigid to
maintain its roundness, while the outer ring 4 for large
fore and aft loads acts as a tensioned band along the part
of the periphery 5' which is forward relative to the ship 1.
The tension in this band 5' is transferred directly into a
tension stay 19, which transfers the tension into the hull
of the ship 1, which in this area is very strong. If the
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tension stay 19 is penetrating the shell plating as shown in
broken lines, the tension strain can be distributed to a
large area.
The load in the band 5' is best equalized if it is flexible
and can con~orm to the rigid surface 4, but there must o~
course be sufficient cross section area in the band to
withstand the tension. The second part 5" of the outer ring
is not loaded by the main force, which is fore and aft
forces pointing aft, but it is reasonable to stiffen it 5"
by means of the plate 23 to absorb the atwarthship forces
which might occur.
Cutouts 24 in the plate 23 can be made to reduce the
vertical wave forces during pitching of the ship 1.
Figure 3 shows a preferred embodiment where the outer ring
20 in the lower bearing is made as a polygon. The drawing
shows a hexagon, but to avoid large point loads against the
inner ring 4, it is preferable to have more sides.
In each corner between two sides a bearing segment 21 is
arranged. The radial force acting on the bearing ~egments
is distributed as tension force in the two adjacent sides.
The maximum fore and aft ~orce transferred to the tension
stay 19 will be the same as in Figure 2. However, the
design using a polygon is simpler because it does not
require fine manufacturing tolerances. The band 5 must be
rolled relatively round, while inaccura~ies in the polygon
20 may be corrected at each bearing segment 21, for instance
by the casting of plastic material 33 behind the bearing
segments, by spacer plates behind each bearing segment, by
individual adaption of steel brackets in the corners, or by
a combination o~ any of these three methods.
The part of the band 20 in the extension of the tension stay
19, will have the same tension as the stay 19, as long as
the total anchoring force is in the fore and aft direction.
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This part is designated 20'. The further course of the band
20 towards the bow of the ship is designated 20".
Figure 4 shows an embodiment where the turret 12 is
extending through the ship. ~he outer ring 2 of the upper
bearing is fastened to a holding device (not shown) in
connection with the deck 16. The bush 32 is here shown
above the inner ring 2, and has a releasable connection 31
to the tube 6. The outer ring 5 in the lower bearing is
connected to the bottom 17 of the ship. The outer ring can
also in this proposal be a polygon 20. When the outar ring
is built into the hull as shown, it is natural that the
periphery acts as a flange to reinforce the cutout in the
bottom 17. However, it is obviously also possible to
arrange a separate reinforcement of the hull and suspend the
outer ring 5, 20 in several tension bands extending in
different directions.
Water will leak through the bearing 4,5 in the bottom, and
20 bulkhead 18 between the bottom 17 and deck 16 must therefore
be arranged to prevent the leakage from proceding.
A vertical watertight shaft 26 can give access for inspac-
tion one by one of the terminations for the anchor lines 8.
In such cases the turret 12 is locked against rotation
relative to the ship 1. The winch 30 can be used to adjust
the tension in the anchor lines 8 through guiding of an
ancillary line through the shaft 26.
A guiding plate 34 is centering the inner ring 4 when it is
to be guided from below into the outer ring 5. A pawl
device 27 which is fixed to the deck 16, can pivot downwards
into one of several notches 28, 28' in the tube 6 to lock
the turret 12 against rotation. The pawl 27 is shown in
broken lines positioned in one of the notches 28.
Figure 5 shows details of the spherical bearing and of the
coupling mechanism on Figure 1. The center 41 o~ the
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spherical bearing 2,3 is shown. Between the sleeve 35 and
~he cover 40 a spherical surface is shown wikh the same
center 41. Actually, there is a narrow gap where this
spherical surface is shown, but if, in an extreme situation,
5 lift should occur on the turret 12, the cover 40 will
counteract at this spherical surface. The bearin~ housing
38 shall be bolted to a reinforcement of the deck 16, - not
shown. The locking mechanism to prevent rotation of the
turret during maintenance works etc. shown in principle by
the pawl 27 and notches 28 on Figure 4, can simply be
arranged by bolts between the cover 40 and the sleeve 35 in
this Figure.
The sleeve 35 externally has several buttress threads 43,
having so large a pitch that the threaded joint is not
selflocking. The shape of the threads are only shown in
section on the right side, while the threads in the section
on the left side are shown dotted. The opposite hub 37 has
internal buttress threads, which are shown in matching
contact sith the threads 43. A dog clutch 36 can slide on
axial splines on the outside of the sleeve 35. One 39 of
several dogs are shown in engaged position against a
matching dog on the hub 37, which is thereby prevented from
rotation relative to the sleeve 35. The dotted contour 36'
shows the upper disengaged p~sition of the clutch 36, when
it is lifted by means of the jack 42 or the hub 37.
Lifting lugs 44 are ~onnected to the hub 37. On the outside
of these lifting lugs are guiding edges 45 which during
entering will guide against a conical guiding surface 46 on
the inside of the sleeve 35 and provide orientation towards
the hub 37.
Figure 6 shows a displayed cylinder section of an area near
the lower end surface of sleeve 35 and the upper end surface
for the hub 37, and how the ends of the threads in this area
can be shaped 47, 47', 48, 48' to secure engagement in all
relative angles o~ rotation.
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The procedure for col~nection of the turret device will then
be as follows.
A line is led from the winch 29 through the upper spherical
bearing 2,3 and further through the outer ring 5 in the
lower bearing, and fastened to the top of the tube 6. The
line must pull approximately in center of the tube, and this
can be achieved for instance by connecting the line to two
or more equal lony rope slings, which are fastened to
lifting lugs 44 arranged symmetrically inside the tube 6.
The turret 12 is lifted form its subsurface position until
the hub 37 on the tube 6 passes the outer ring in the lower
bearing, and further until the hub 37 is in position for
entering the sleeve 35. I~ the hoisting line is pas~ing
approximately through the center of the upper bearing, the
conical guiding surface 46 of the sleeve 35 will be guided
by edges 45 of the hub 37 when it is lifted further. The
sleeve 35 then deflects in the spherical bearing. When the
guiding edges 45 have passed the conical guiding surface 46,
the first threads of the sleeve 35 and the hub 37 can be in
contact. The contact pressure will cause the slee~e 35 to
deflect until it is axial with the hub 37, and all the
- threads will then be in contact.
Further hoisting of the hub 37 causes the sleeve 35 to
rotate. During the last part of the rotation, the hub 37
will push the dog clutch 36, but when the dog clutch reaches
th~ dotted position 36', the dogs 39 enter the zone for
engagement with the hub 37, and the dog clutch 36 is falling
*y gravity to the position shown. The dogs 39 will then
prevent further rotation of the sleeve 35 in both direc-
tions.
Simultaneously with the entering of the coupliny at the
upper spherical bearing, the cone 14 has guided the inner
ring 4 of the lower bearing into the outer ring 5.
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Thereafter the tension in one by one or two and two o~ the
anchor lines 8 can be adjusted by means of one or two
winches 30. Before this operation, the ship must be turned
by means of tugs or its own propeller equipment, and the
turret locked by means of the pawl 27 or the like in the
correct position. It is also possible to do a complete
tensioning of all anchor lines in this way if the anchors
are deployed by another ship.
A line which in advance is led through the tube 6 and
~astened to an easily accessible spot on the bottom plate 7,
is loosened from the bottom plate and connected to the riser
pipe 9. ~hereafter the rlser pipe is hoisted by means o~
the winch 29 and connected to the shipls pipe sy5tem through
the swivel lo. When a flexible riser pipe is used, it is
also possible to have it attached inside the tube 6.
When disconnecting the turret, this can be done according to
two procedures, either by controlled lowering by means of
the winch 29, or as a free drop whers the water resistance
is the brake. Solutions adopting part solutions from both
the described procedures can also be used.
By controlled lowering of the turret, the riser pipe 9 is
first disconnected from the swivel lO and lowered by the
winch Z9, and marked with a small buoy. The marking buoy
can for instance be connected to the bottom plate 7 and have
a line connection through the pipe 6.
Thereafter a line from the winch 29 is fixed to the turret,
and the winch is hoisting until it holds khe vertical force
from the turret 12. Jacks 42 can then lift the dog clutch
36, and the turret is lowered until it has found its natural
position of equilibrium below water. The line is discon-
nected from the winch and connected to a marking buoy with
- an ancillary line. The marking buoy can for instance be
placed on deck and connected to an ancillary line led
downwards along the ship side and further between the
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polygon outer ring 20, a bearing segment 21, 3 3 and the
inner ring 4 to an area near deck where it can easily be
reached.
5 By the second procedure, the riser pipe 9 may for instant be
fixed to the tube 6, so that it can simply be disconnected
from the swivel 10. Marking buoy with line can be prepared
in advance on the turret. By activation of the hydraulic
jacks 42 th~ dog clutch 36 is pressed out, and the turret is
dropping under the action of gravi.ty and the vertical force
from the anchor lines, but braked by the water resistance
and the buoyancy until it finds its natural equilibrium.
