Note: Descriptions are shown in the official language in which they were submitted.
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1 STABILIZED MONOHULL VESSEL
This application relates to a vessel, preferably for
petroleum activities, with carrying capacity generally
comprised by one single hull, carrying a main deck and
6 arranged for use in marine petroleum activity with treatment
and storage of petroleum fluids both on the field and
accosted under land.
More specifically, the application is on a large
monohull vessel being applied for several different
11 processes, e.g. a so-called "FPSO"; a floating production,
storage and off loading vessel, also performing processing
of petroleum fluids, or a conversion plant especially for
conversion of petroleum fluids to other, preferably fluid
petroleum products, and not necessarily chemical processes
16 but also physical processes, e.g. cooling to LNG. The vessel
is arranged for use both connected to the oil producing
field via pipelines connected at a rotating turret in the
vessel. The vessel also has a plane transom stern, thus it
may lie with its stern to the quay.
21 In this way dead time is avoided during well work over
and halted petroleum production, in that the vessel may be
moved to other wells or along the quay where it may work
with petroleum fluids delivered from gas storage tanks
onshore. At the same time the vessel will be arranged with
26 large storage tanks 11 for petroleum fluids in order to have
a buffer capacity both. if it in periods must receive more
petroleum fluid than what can be processed, or if there are
discontinuities in the reception petroleum fluid to be
processed. The tanks 11 may be arranged with bulkheads and
31 baffle plates and a design of the free surfaces in order to
work out of phase with the vessel s rolling and pitching.
Under stationary operation at sea, especially with a
vessel performing continuous work in rough sea, the vessel
will experience rolling, pitching and heave movements due to
36 the waves. The rolling, pitching and heave movements will
normally have each their dominating or natural frequency.
Swell will also lead to slow rolling and heave even in calm
sea. Periodic rotation movements as rolling and pitching are
generally disadvantageous in that pressure, flow and forces
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1 in all processes on board vary due to the more or leas
periodic accelerations and rotations. It is also
disadvantageous to the crew and their work operation that
the vessel rolls and pitches. If these vessel movements are
reduced in amplitude and frequency, the work on board may
6 generally be done better and more efficiently. Further the
wave movements from the vessel will propagate further to
pipelines connecting the vessel with wells on the seabed,
and to anchoring devices. It is desirable to reduce these
vessel movements to a large extent. By reducing the vessel
11 movements for such a vessel the tolerance of the vessel for
bad weather is extended, so that operations which under the
known art must be interrupted due to the weather, may be
restarted earlier on dropping wind, and to be interrupted
later on increasing wind. A vessel according to the present
16 invention will thus have a longer proportion of operation
time at harsh weather conditions. An additional moment of
the invention is that by reduced roll- pitch and heave
movements the load due to vertical acceleration and bending
of risers, coiled tubing, and load on drilling fluid pumps,
21 moorings and other equipment, is reduced to a lower level
than by using vessels according to known art.
Such problems with roll, pitch and heave moments and
other wave movements may be counteracted by using the
present invention comprising a vessel, preferably for
26 petroleum processing and storage, which carrying capacity
primarily is comprised by one single hull, with a main deck,
and where the new and inventive trait is comprised by one,
essentially horizontal dampening device reaching out on
either side of the hull, under the water line, extending
31 preferably along the entire length of the hull.
Further inventive traits by the vessel is to be found
in the subordinate claims.
A vessel according to the invention will for this
purpose be very large and is arranged to carry a production
36 plant and a processing or conversion plant for petroleum
fluids, i.e. gasses and liquids. Several of these processes
depend on stabile and relatively predictable pressure
conditions. In addition to the fact that the vessel will
have reduced roll and heave, parts of the vessel's after end
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1 according to the invention will have an area of reduced
heave, partly at the cost of a little increase of heave for
the bow because the dampening device in the preferred
embodiment of the vessel increases in width sternwards along
the ship s side, and in addition cooperates with a second
6 dampening device at the stern. However, the size of the
vessel will do that the weakly increased heave motion of the
vessel will not give a considerable disadvantage. Also there
will not be performed any processing activity in the bow
area because the vessel according to a preferred embodiment
11 will have its crew section in the bow towards the weather
due to small amounts of gas which can leak from such a large
processing device.
Another purpose with the vessel is that it shall be
able to store petroleum fluids immediately after production
16 from wells on the seabed and deliver and load petroleum
fluids, either directly, or in processed form further to
shuttle tankers which can tie up to transfer lines astern on
this vessel. The width of the vessel s stern will then
function as a breakwave where shuttle tankers may be
21 situated completely or partly leeward of the vessel because
the vessel in a preferred embodiment is designed to be
turned with the bow towards the present weather, i.e. the
combination of waves and wind.
The invention will below be described with reference to
26 figure drawings, where:
Fig. 1 describes schematically a horizontal plane
view and section of the entire hull with a
dampening devices according to the invention,
Figs. 2 and 2b describe schematically a vertical right-to-
31 left section at A-A', about astern of midship
of the vessel,
Fig. 3 describes schematically a vertical
athwartships section by B-B' a little afore
of the transom stern.
36 Fig. 4 displace a plane section of the main deck
with the vessel situated with the stern
alongside the quay.
Fig. 5 shows a long section along the vessel and the
front of the quay with the vessel lying
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1 ballasted down to a fundament on the seabed.
Fig. 6 shows a sketch of a situation with a vessel
according to the invention stationary in the
open sea over a petroleum fluid producing
well.
6 Fig. 1 describes a schematic plane view and section of
the vessel according to the invention with a waterline
section of a hull 3, and the plane view showing dampening
devices 2 arranged below the waterline. The hull 3 has in a
preferred embodiment even width, but may in alternative
11 embodiments have other development of the width from the bow
to the stern. The vessel has, afore of the midship, a
rotating turret 14. The vessel's stern 32 is primarily plane
and vertical, with a concave cavity 34 in the lower part of
the transom stern 32 with the lower side of the cavity
16 comprised by a dampening device 2~. By the vessels stern the
hull's cross section is extended by projections for
extending generally in the entire height of the vessel from
the bottom plate 40 and up to the main deck 1. The purpose
with these projections 40 is to increase the vessel's
21 directional stability so that it will direct itself towards
the weather when it is moored at sea by means of mooring
devices 400, via the rotating turret 14, e.g. when the
vessel via and production risers 200 is situated connected
to a well at the seabed with petroleum fluids.
26 Fig. 2 and Fig. 3 show vertical cross sections of the
vessel, with the wings or dampening devices 2 in the
preferred embodiment arranged in level with the essentially
plane bottom plate 40 of the vessel. In the hull's 3 stern
there is a concave cavity 34, with bottom of the cavity
31 comprised by a second dampening device 2', which in a
preferred embodiment generally is arranged in level with
bottom plane 40 of the vessel. Due to that the dampening
devices 2 and 2' are in level with and do not reach deeper
than the vessel's bottom plane 40 the possibility exist to
36 ballast the vessel and to set it down on a foundation along
the quay. Because the dampening devices 2 and 2' are
preferably plate shaped and horizontal, they counteract both
rolling, pitching and heave, contrary to if they should have
been arranged vertically, a situation where they would not
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1 be able to counteract pitching and heave to a considerable
degree. The vessel's hull 3 and dampening device 2 and 2~
may be designed in steel, but it is in a preferred
embodiment also possible to build considerable parts of the
vessel in armed concrete. For vessels for the purposes as
6 described above, it is desirable to have a deck area which
is as large as possible and plane o the main deck 1. The
vessel has a large width of the main deck 1. In a preferred
embodiment the main deck has an even width generally from
bow area and the entire length back to the main deck's 1 end
11 entirely at the stem of the vessel. This also reduce the
risk that a wave coming in from the front and being higher
than the freeboard to break in over the main deck 1 astern.
The vessel's hull has a considerably narrower width of the
hull 3 in the waterline than the main deck. This contributes
16 to dampen the effect of vertical movements of the sea so
that the vessel does not heave as much as it would have done
with a larger area inside the waterline.
The purpose with and the effect of the dampening
devices 2 and 2' is to dampen the vessels roll- and pitching
21 movements by dispersing the wave forces and the water flow
around the hull 3, but will also contribute to a certain
dampening of heave (vertical movement). As mentioned above
there will arise a "zero point area" for the vertical
movement somewhere centrally on the stern part of the main
26 deck 1, at the price of a certain increased vertical
acceleration in the bow part. In this area with reduced
vertical accelerations the processing or conversion
equipments demanding the most stabile fluid conditions may
be arranged.
31 Fig. 2 shows a schematic view and vertical cross
section through the vessel, with the dampening devices 2
shown in section. One or more vertical openings 22 in the
dampening device 2 are arranged for permitting a limited
vertical flow-through of water and thereby give a dampening
36 of the waves effect on the vessel, and at the same time to
disperse the energy of the waves. In addition the vessels
rotation moment of inertia around the vessels main axis is
increased due to two reasons:
1: A large mass is added represented by the dampening
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1 devices 2 situated thwartships of the vessels main axis and
with a large separation from the main axis.
2: A certain water mass is bound over each of the
dampening devices 2, which are forced to partly follow the
vessel's rotation movement when the dampening device 2 is on
6 its way alternately at the starboard and the port side when
the vessel rolls.
In addition to that vessel's rolling movements are
dampened in amplitude and frequency due to that the rotation
moment of inertia of the vessel increases, the rolling
11 movements will be hampered by the dampening devices friction
against the water masses due to the water's viscosity when
the water is to be forced outside the dampening devices
alter edge and through the openings 22.
A standing rim 24 on the dampening device 2 will
16 contribute to reduce the overlying water masses (in relation
to the dampening devices 22) possibility to flow sidewards,
so that these water masses to a larger degree of forced with
the rolling movement of the vessel.
Additional dampening of the vessel's rolling may be
21 achieved by arranging air filled tanks 26, shown in Fig. 2b,
with opening only down toward the water, at either side of
the vessel. The tanks 26 may have an alter wall 26'. Such
stabilizing tanks 26 may be designed in under and in
cooperation with the overhanging main deck 1 of the vessel
26 out over the hull 3 outer side, and also to stiffen up the
dampening devices 2 by means of vertical plates 26" standing
between the hull 3 or main deck 1 and dampening devices 2.
In an alternative embodiment it is possible to let
stabilizing tanks 26 outer wall 26~ extend entirely or in
31 partial connection with the standing rim 24. When the vessel
rolls the water surface will press up the air pressure or
suction down the air pressure in the air column which is
locked above the water surface and below the top of the
tanks 26, which may be comprised by the hull's 3 upper
36 projection or the underside of the main deck 1.
Clearly the vessel must be designed so large that the
vessel's width is made preferably larger than the pronounced
wave length which one wishes to avoid rolling with. Such a
vessel with such a dampening device 2 will namely be forced
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1 to roll in phase with waves of a certain wavelength range in
the order of the vessel's width.
It is also possible to design the dampening devices 2~
astern edge 21~ towards the sea so that it extends like a
generally convex ark 21~ out from the vessel's stern 32,
6 arranged for rejecting vessels which would come too close to
the stern 32.
In alternative embodiments, dampening device 2 and 2~
may consist of a frame with a lattice with several
horizontally arranged lying plates with mutual separation or
11 a grating of similar shape.
In a preferred embodiment the vessel is not designed to
have its own propulsion engines but is designed to have
propulsion by means of tender vessels. It will need tender
vessels during transit. In a preferred embodiment the vessel
16 has power devices 8 for emergency propulsion and dynamic
positioning. The hull 3 is hydrodynamically designed to be
able to lay with the bow 33 towards the weather. Such power
devices may be so-called azimuth thrusters" with horizontal
propeller axle arranged on a rotatable vertical stem
21 comprising a vertical axle and gears, having the propeller
power working freely rotatable through 360° all around the
horizon. These power devices are in a preferred embodiment
arranged astern at the starboard and port side of the hull 3
extending out through the bottom plane 40 under the
26 projections 4. The projections 4 will give the vessel good
directional stability with respect to the direction of the
dominating weather, and reduce the need for machine power to
lie in a good position towards the weather.
Fig. 4 shows a schematic plane view of the vessel
31 situated by the quay. The dampening device 2 has in a
preferred embodiment several vertical openings 22 arranged
to allow a limited vertical water through flow and thus
imposes dampening of the waves~ effect on the vessel. These
openings are designed according to actual wave- and current
36 conditions for ordinary operation. The dampening device 2
(2 ~ ) with the openings 22 (22 ~ ) will thus counteract and
partially delay the flow-through of water and thus work as a
fluid mechanical filter, especially on the vessel's
sidewards rolling, and also vertical movement or heave, and
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1 also pitching. The effect of the filter is mathematically to
reduce the high frequent amplitudes of the vessel's rolling
and heave.
An important prerequisite of the invention is that the
vessel shall comprise a transom stern 32 arranged to lie
6 along a quay, shown in Fig. 5. Devices 340 are arranged for
transport of materials in solid and fluid form, and energy,
mainly between the vessel s stern and the onshore when the
vessel is situated by the quay. The vessel may in this
position under land receive gas from storage tanks or gas
11 pipelines onshore, convert the gas to fluid petroleum
products, e.g. diesel oil, which it exports onshore in to
the quay afterwards. Fig. 5 shows further that the vessel
may be arranged to lie on foundations at the seabed. An
alternative solution is to moor the vessel in the ordinary
16 way with bow moorings out into the sea and stern or quarter
fast towards the quay.
When the vessel is moored on the field, it may be
moored by means of mooring devices 400, e.g. with anchor
lines between the rotating turret 14 and suction anchors in
21 the seabed, and such that the vessel receives petroleum
fluids from wells on the seabed via risers 200. Together
with the risers 200 there may also be arranged signal- and
energy carriers for well control. Such a situation may be
illustrated by Fig. 6, showing how the vessel may lie on the
26 weather and convert gas which is being received through the
pipelines 200. The gas is converted by means of a gas
conversion plant 220 to other petroleum fluids.
One may think of other purposes for the vessel than
using it for gas converting and storage ship on an oil
31 field. However, other applications in an oil field will not
be significantly different from the present invention.
The bottom 40 of the vessel is in the invention not
bound to be plane or horizontal and the dampening devices 2
are not either limited to lie level with the bottom or to
36 have entirely plane shape or to lie entirely horizontal.
