[0001] In a first aspect the present invention relates to a vessel comprising a system for
transferring persons or goods from the vessel while subjected to waves and/or swell
towards a substantially stationary destination, wherein the system comprises a platform
for supporting the persons or goods during transfer, and platform actuators connecting
the platform to the vessel and adapted for moving the platform relative to the vessel
in such a manner that the platform is maintained spatially in a substantially stationary
position.
[0002] Its main field of use is offshore industry where it is a known problem to transfer
persons or goods from a vessel which moves in consequence to the influence of, among
others, the swell, waves, currents and wind relative to a (substantially) stationary
destination such as, for example an offshore drill rig, offshore wind turbine or another
large vessel.
[0003] In response to this problem a vessel has been developed in accordance with the preamble
of the main claim. Such a vessel is known from
WO2007/120039.
[0004] The known system comprises a movable platform, a so called Stewart platform, which
is actuated by six piston-cylinder assemblies in response to the motions of the vessel,
in such a manner that the platform maintains a (substantially) stationary spatial
position, thus a stationary position relative to the stationary destination. For the
actual transfer of the persons or goods the platform may be provided with a gangway,
crane or alike.
[0005] It has appeared that during use of such a vessel the platform and platform actuators
are constantly activated for achieving the desired compensation and thus exert considerable
forces of inertia onto the vessel. Especially in case of lightly damped vessel motions
(such as rolling for monohull vessels and also pitching for multihull vessels) this
may prove disadvantageous. This situation may even be worse because vessels with respect
to such barely damped motions move at or near to their natural frequencies and the
excitation by the platform activators occurs exactly at those frequencies. As a result
of the occurring resonance rather small excitations already may lead to large amplitudes
of the resulting vessel movements.
[0006] It is an object of the present invention to provide an improved vessel of the above
type and to prevent or diminish occurring resonance effects.
[0007] Thus, in accordance with the present invention a vessel is provided which is
characterized in that the system further comprises at least one compensation mass for at least partially
compensating motions of the vessel caused by the activation of the platform actuators
and by the resulting motion of the platform relative to the vessel, wherein a compensation
actuator couples the at least one compensation mass to the vessel for a movement relative
thereto.
[0008] The compensation actuators compensate the excitations of the vessel caused by the
accelerations of the platform and platform actuators, by moving the at least one compensation
mass in such a manner that the mentioned excitations are counteracted by opposite
excitations.
[0009] In one embodiment of the vessel the compensation actuator is adapted for counteracting
a rotational motion of the vessel around at least a first axis of rotation. For example
it is conceivable that the compensation actuator is adapted for counteracting a rolling
and/or pitching movement of the vessel.
[0010] In another embodiment of the vessel it is possible that the at least one compensation
mass is adapted to be moved linearly by its compensation actuator(s).
[0011] The at least one compensation mass may comprise multiple masses, each with dedicated
compensation actuator(s). For example, two compensation masses may be provided which
are adapted to be moved linearly by their respective compensation actuators substantially
in parallel to the longitudinal axis of the vessel and in parallel to transverse axis
of the vessel, respectively. These masses may be used primarily to counteract longitudinal
and transverse motions of the vessel.
[0012] In such a case it is conceivable too, that both compensation masses are combined
into a single mass which is adapted to carry out the linear movements in parallel
to the longitudinal axis of the vessel and in parallel to transverse axis of the vessel,
respectively.
[0013] Constructively, it is advantageous when the compensation actuators comprise assemblies
of linear guides and linear actuators. However, also other devices for achieving a
linear motion of the compensation mass or masses may be used.
[0014] In yet another embodiment of the vessel according to the present invention the compensation
actuators are adapted for offering the at least one compensation mass a rotational
movement with three degrees of freedom and a linear movement with three degrees of
freedom. This offers the compensation mass a full range of movements for compensating
nearly all excitations of the vessel.
[0015] In such a case it is possible that the compensation actuators comprise six linear
actuators, such as hydraulic or pneumatic piston cylinder assemblies which each at
both ends by means of universal joints are connected to the vessel and the at least
one compensation mass, respectively. Basically, such an arrangement will correspond
with a known arrangement of actuators used to move the platform.
[0016] In a special embodiment of the vessel according to the present invention, the at
least one compensation mass is defined by an auxiliary platform moved by auxiliary
platform actuators substantially similar to the platform and platform actuators and
adapted to be moved substantially in counter phase to the motion of the platform and
platform actuators. The auxiliary platform and auxiliary platform actuators will counteract
(and compensate) the excitation caused by the platform and platform actuators.
[0017] To be most effective, a compensation mass theoretically should coincide with the
platform and platform actuators; however, because of possible concurrent technical
difficulties of such a theoretical arrangement, in practice there will be a small
distance between those parts of the system. Thus, in accordance with another embodiment,
the at least one compensation mass may be located substantially at the same level
as and close to the platform and platform actuators. The relative position between
those parts then may be optimised with respect to the best compensation of the excitation
in view of the most important movement of the vessel (for example rolling in monohull
vessels and pitching in multihull vessels).
[0018] In another embodiment of the at least one compensation mass is located below the
platform and platform actuators. Also in such a case the compensation mass may comprise
an auxiliary platform moved by auxiliary platform actuators substantially similar
to the platform and platform actuators; but also other types of a compensation mass
are conceivable, for example using linear guides and linear actuators.
[0019] In yet another embodiment, the vessel further comprises control means for controlling
the compensation actuators of the at least one compensation mass adapted to generate
control signals for said compensation actuators based upon the movement of the platform.
Such an embodiment directly uses the movement of the platform (for example based upon
the control signals for its platform actuators) to generate the required control signals
for the compensation actuators of the compensation mass.
[0020] However, it is possible too that the vessel further comprises control means for controlling
the compensation actuators of the at least one compensation mass, which control means
comprises sensors for sensing the motion of the vessel and means for generating control
signals for said compensation actuators based upon an output of said sensors. As a
result also the movements of the vessel (irrespective the origin thereof, for example
due to the activation of the platform or due to environmental influences such as waves,
current or wind) are used as an input to generate control signals for the compensation
actuators of the at least one compensation mass.
[0021] Then, in one embodiment of the vessel, the control means may be adapted to generate
control signals for said compensation actuators for counteracting rolling and pitching
of the vessel. But also other movements of the vessel (depending on the type of vessel)
may be compensated.
[0022] In a second aspect, the present invention relates to a system for transferring persons
or goods from a vessel towards a substantially stationary destination for use on a
vessel according to the present invention. According to the present invention such
a system comprises a platform for supporting the persons or goods, and platform actuators
adapted for connecting the platform to the vessel and moving the platform relative
to the vessel in such a manner that the platform is maintained spatially in a substantially
stationary position, and further comprising at least one compensation mass for at
least partially compensating motions of the vessel caused by the activation of the
platform actuators and by the resulting motion of the platform relative to the vessel,
and compensation actuators mountable to the vessel and to the at least one compensation
mass for a movement thereof relative to the vessel.
[0023] Hereinafter the invention will be elucidated by means of the drawing, in which:
Figure 1 schematically shows a first embodiment of a system for transferring persons
or goods according to the present invention,
Figure 2 schematically shows a second embodiment of a system for transferring persons
or goods according to the present invention.
Figure 3 schematically shows a third embodiment of a system for transferring persons
or goods according to the present invention, and
Figure 4 schematically shows an embodiment of a compensation mass as it can be mounted
on one or more locations of the vessel.
[0024] Referring to figure 1 only a small part of a vessel 1 is illustrated showing a system
for transferring persons or goods from the vessel towards a substantially stationary
destination mounted on an upper deck. Such a system generally comprises a platform
2 for supporting the persons or goods, platform actuators 3 connecting the platform
2 to the vessel 1 and a gangway 4 mounted on the platform 2.
[0025] The platform actuators 3 (which for example may comprise six fast acting pneumatic
or hydraulic piston cylinder assemblies) are adapted for moving the platform 2 relative
to the vessel 1 in such a manner that the platform is maintained spatially in a substantially
stationary position, notwithstanding a movement of the vessel 1 due to external influences
such as, among others, the swell, waves, and wind. As a result the platform 2 may
be kept stationary relative to a (substantially) stationary destination (such as,
for example an offshore drill rig, offshore wind turbine or another vessel) and persons
or goods may be transferred in a safe manner to said stationary destination (for example
by means of the gangway 4).
[0026] The system as described up to this point corresponds with a well known system for
transporting people from a ship to a stationary construction located at sea as used
on vessels to date. In accordance with the present invention, such a system further
comprises at least one compensation mass for at least partially compensating motions
of the vessel 1 caused by the activation of the platform actuators 3 and by the resulting
motion of the platform 2 relative to the vessel.
[0027] In the embodiment according to figure 1 there is a single compensation mass which
by means of compensation actuators is mounted to the vessel for a movement relative
thereto. The compensation mass is defined by an auxiliary platform 5 (which may or
may not be similar to the primary platform 2; it is conceivable, for example, that
the auxiliary platform is defined by a mass with the same mass and inertia as the
primary platform, but without exactly the same outer appearance; as such a gangway
generally will not be present).
[0028] The compensation actuators are defined by auxiliary platform actuators 6. As is the
case with the platform 2, the compensation actuators 6 preferably comprise six (linear)
actuators, such as hydraulic or pneumatic piston cylinder assemblies which each at
both ends by means of universal joints 7 are connected to the vessel 1 and to the
at least one compensation mass 5, respectively.
[0029] The auxiliary platform 5 and auxiliary platform actuators 6 are adapted to be moved
substantially in counter phase to the motion of the platform 2 and platform actuators
3. As such, the compensation mass may be adapted for counteracting a rotational motion
of the vessel 1 around at least a first axis of rotation (for example for counteracting
a rolling and/or pitching of the vessel).
[0030] Basically the compensation actuators 6 according to the embodiment of figure 1 are
adapted for offering the compensation mass (auxiliary platform) 5 a rotational movement
with three degrees of freedom and a linear movement with three degrees of freedom.
For compensating the movement of the vessel 1 caused by the forces generated by the
system for transporting people from the ship to the stationary platform in general
only the rotation around the longitudinal axis of the vessel 1 and/or the rotation
around a horizontal axis perpendicular to the longitudinal axis need to be compensated
as due to the shape of the vessel 1 that are the only movements that might show increasing
oscillations as a result of the forces earlier mentioned. In situations that the compensation
mass 5 compensates only for rotation around one or two axis it is sufficient to let
this compensation mass 5 rotate around one or two axis and linear movements of the
compensation mass 5 are not required. The number of compensation actuators can than
be reduced to one or two compensation actuators 6 that let the compensation mass 5
oscillate in one or two orthogonal planes respectively.
[0031] In the illustrated embodiment the compensation mass 5 is located immediately below
the platform 2 and platform actuators 3 (specifically below the upper deck of the
vessel 1), but it is conceivable too that it is located substantially at the same
level as (and preferably close to) the platform 2 and platform actuators 3. In a further
embodiment, a smaller compensation mass 5 might be located in front or behind the
platform 2 or at both sides of platform 2.
[0032] The system further may comprise control means (not illustrated) for controlling the
compensation actuators 6 of the compensation mass 5, adapted to generate control signals
for said compensation actuators 6 based upon the movement of the platform 2 (and the
movement of the platform actuators 3). Further additional control means (not shown)
may be provided, also for controlling the compensation actuators 6 of the compensation
mass 5. Such additional control means may comprises sensors(not illustrated) for sensing
the motion of the vessel 1 and means for generating control signals for said compensation
actuators 6 based upon an output of said sensors. As a result control signals for
the compensation actuators 6 may be calculated in such a manner that the compensation
mass (auxiliary platform) 5 carries out a movement for in an optimal manner compensating
(counteracting) an excitation caused by the movement of the platform 2 at one hand,
and an excitation caused by a movement of the vessel 1 at the other hand (which may
be caused by the movement of the platform 2 but also by external influences, such
as wind, current and waves).
[0033] Of course it is also possible that the control signals for the compensation actuators
6 of the compensation mass 5 are directly derived from the original control signals
for the platform actuators 3 (for example having substantially the same magnitude
but an opposite sign, depending on the characteristics of the system in general and
of the compensation mass in specific).
[0034] Referring to figure 2, a second embodiment of a vessel with system according to the
present invention is illustrated. The upper part of the system (which, basically represents
a state of the art system) is similar to the system for transporting people from a
ship to a stationary construction located at sea as described before and therefore
the description thereof is not repeated.
[0035] The lower part of the system according to this second embodiment comprises two compensation
masses 8,9 which are adapted to be moved linearly by respective compensation actuators
10,11 (for example in parallel to the longitudinal axis of the vessel 1 and in parallel
to transverse axis of the vessel, respectively). The compensation actuators 8,9 (which
may comprise any type of linear actuators, such as for example cylinder piston assemblies,
cable drives, gear racks) are devised for moving the compensation masses 10,11 to
and fro, for example along linear guides 12,13 attached stationary to the vessel 1
and located immediately under the upper part of the system, for instance immediately
under the upper deck.
[0036] Although this second embodiment shows two separate compensation masses each adapted
for a to and fro movement in a specific direction, it is also conceivable that both
compensation masses 8,9 are combined into a single mass which is adapted to carry
out linear movements in different directions (for example in parallel to the longitudinal
axis of the vessel and in parallel to transverse axis of the vessel, respectively)
and, thus, in combination may carry out movements in any other direction (in a plane
extending through said two original directions) or even along a curved trajectory,
if needed (in said plane).
[0037] The operation of this second embodiment generally is similar to that of the first
embodiment (although, because this embodiment only allows the compensation mass or
masses to be moved in a more restricted manner, its capability for compensating or
counteracting excitations may be less). Control means and sensors may be provided
in accordance with the first embodiment.
[0038] Referring to figure 3 a third embodiment of a vessel with system according to the
present invention is illustrated schematically. The figure 3 shows the vessel 1 with
a platform 14 mounted on the rear of the vessel. Platform actuators 15 move the platform
14 and maintain the platform 14 in a stationary position while the ship moves in waves
and/or swell. It will be clear that the platform 14 can rotate on a turret 18 that
is mounted on the deck, that the platform 14 can move in height by changing its inclination
and that the length can be adapted as required. In the shown embodiment transverse
compensators 16 are mounted on deck in front and at the rear of the turret 18 and
the longitudinal compensators 17 are mounted under the deck. In other embodiments
these positions can be different and are dependent on the available space and the
required compensation.
[0039] Referring to figure 4 an embodiment of a compensation mass as it can be mounted on
one or more locations of the vessel is illustrated schematically. In the embodiment,
an actuator 20 can move a mass 19 can move over a rail. As shown the actuator 20 comprises
a motor, for instance a hydraulic motor, that drives a gear that engages a rack mounted
in the direction of the rail. The actuator 20 and the mass 19 are mounted under a
cover 21 to protect them against the environment.
[0040] The invention is not limited to the embodiments described before, which may be varied
widely within the scope of the invention as defined by the appending claims. For example,
the compensation mass may have a mass which differs from the mass of the platform
(with or without its actuators) and may be moved in any other appropriate manner,
for example as a pendulum with a pendulum arm with specific length by means of three
linear actuators positioned around said pendulum arm.
1. Vessel comprising a system for transferring persons or goods from the vessel while
subjected to waves and/or swell towards a substantially stationary destination, wherein
the system comprises a platform for supporting the persons or goods during transfer,
and platform actuators connecting the platform to the vessel and adapted for moving
the platform relative to the vessel in such a manner that the platform is maintained
spatially in a substantially stationary position, characterized in that the system further comprises at least one compensation mass for at least partially
compensating motions of the vessel caused by the activation of the platform actuators,
wherein a compensation actuator couples the at least one compensation mass to the
vessel for a movement relative thereto.
2. Vessel according to claim 1, wherein the compensation actuator is adapted for counteracting
a rotational motion of the vessel around at least a first axis of rotation.
3. Vessel according to claim 2, wherein the compensation actuator is adapted for counteracting
a rolling and/or pitching movement of the vessel.
4. Vessel according to any of the previous claims, wherein the at least one compensation
mass is adapted to be moved linearly by its compensation actuator(s).
5. Vessel according to claim 4, wherein the at least one compensation mass comprises
multiple masses, each with dedicated compensation actuator(s).
6. Vessel according to claim 5, wherein two compensation masses are provided which are
adapted to be moved linearly by their respective compensation actuators substantially
in parallel to the longitudinal axis of the vessel and in parallel to transverse axis
of the vessel, respectively.
7. Vessel according to claim 6, wherein both compensation masses are combined into a
single mass which is adapted to carry out the linear movements in parallel to the
longitudinal axis of the vessel and in parallel to transverse axis of the vessel,
respectively.
8. Vessel according to any of the claims 4-7, wherein the compensation actuators comprise
assemblies of linear guides and linear actuators.
9. Vessel according to any of the previous claims, wherein the compensation actuators
are adapted for offering the at least one compensation mass a rotational movement
with three degrees of freedom and a linear movement with three degrees of freedom.
10. Vessel according to claim 9, wherein the compensation actuators comprise six linear
actuators, such as hydraulic or pneumatic piston cylinder assemblies which each at
both ends by means of universal joints are connected to the vessel and to the at least
one compensation mass, respectively.
11. Vessel according to any of the previous claims, wherein the at least one compensation
mass is defined by an auxiliary platform moved by auxiliary platform actuators substantially
similar to the platform and platform actuators and adapted to be moved substantially
in counter phase to the motion of the platform and platform actuators.
12. Vessel according to any of the previous claims, wherein the at least one compensation
mass is located substantially at the same level as and close to the platform and platform
actuators.
13. Vessel according to any of the claims 1-11, wherein the at least one compensation
mass is located below the platform and platform actuators.
14. Vessel according to any of the previous claims, further comprising control means for
controlling the compensation actuators of the at least one compensation mass adapted
to generate control signals for said compensation actuators based upon the movement
of the platform.
15. Vessel according to any of the previous claims, further comprising control means for
controlling the compensation actuators of the at least one compensation mass, which
control means comprises sensors for sensing the motion of the vessel and means for
generating control signals for said compensation actuators based upon an output of
said sensors.
16. Vessel according to claim 15, wherein the control means are adapted to generate control
signals for said compensation actuators for counteracting rolling and pitching of
the vessel.
17. System for transferring persons or goods from a vessel towards a substantially stationary
destination for use on a vessel according to any of the previous claims, comprising
a platform for supporting the persons or goods, and platform actuators adapted for
connecting the platform to the vessel and moving the platform relative to the vessel
in such a manner that the platform is maintained spatially in a substantially stationary
position, and further comprising at least one compensation mass for at least partially
compensating motions of the vessel caused by the activation of the platform actuators
and by the resulting motion of the platform relative to the vessel, and compensation
actuators mountable to the vessel and to the at least one compensation mass for a
movement thereof relative to the vessel.