[0001] The present invention relates to a port ramp having a pontoon float, and forming
a connecting path between a roll-on/roll-off ship and a quay in a harbour installation
being subjected to variations in water level, and wherein a ramp bridge is vertically
pivotably connected to the edge of the quay and to the pontoon respectively.
[0002] Port ramps having a pontoon float are normally used as a connecting path between
ship and quay when loading and unloading roll-on/roll-off ships in harbours being
subjected to variations in water level, e.g. caused by the tides. A port ramp of this
kind is known, e.g. from SE-A 415.583. This prior construction comprises a comparatively
large pontoon float. The reason for this large float is primaly to minimize the trim
movements occuring when a heavy vehicle is moving over the pontoon float. Modern handling
of goods into and from a roll-on/roll-off ship implies horizontal transfer of heavy
goods units, resulting in assymmetrical loading of the pontoon float, in relation
to its centre of floatation. From this follows trimming which must be minimized in
order to reduce the stresses on the ramp and enable vehicle movement. The large pontoon
floats necessary for this effect is, however, expensive to build and is space consuming
in a harbour installtion. SE-A 419.741 discloses a device for reduction of heeling
forces on a pontoon float, who are caused by a load passing over it. This device uses
a system with chains, counterweights and a balance mass to balance the heeling moment
caused by a load moving over the pontoon float. The benefits of this device, i.e.
the possibility to reduce the size of the pontoon float, is limited by that the weight
of the balance mass and the chains have to be carried by the pontoon float. Further,
this arrangement is expensive and rises the cost of maintenance.
[0003] The object of the present invention is to provide a device making it possible to
reduce both size and cost of a pontoon float affording a vehicular track for handling
of roll-on/roll-off cargo, and with excellent trim characteristics.
[0004] According to the invention the port ramp is characterized in that at least one hydraulic
cylinder s pivotably mounted between the ramp bridge and the pontoon float, that both
hydraulic cylinder fluid chambers are interconnected via at least one check valve
and connected to a fluid reservoir, in order to slow down the speed of pivot angle
variations between the ramp bridge and the pontoon float, so that these together
form an interconnected, rigid unit in relation to the load produced by vehicles intermittently
moving over the pontoon float, as well as independently pivotable units in relation
to the action of variations in water level, e.g. caused by the tides.
[0005] Preferably, the damping means comprize at least one hydraulic cylinder, which is
pivotably mounted between the ramp bridge and the pontoon float.
[0006] According to another preferable embodiment of the invention, the hydraulic cylinder
fluid chambers are interconnected via at least one check valve and connected to a
fluid reservoir.
[0007] One embodiment of the invention will now be described with reference to the accompanying
drawings, wherein:
Fig. 1 is a side view of a port ramp according to the invention,
Fig. 2 diagrammatically illustrates a hydraulic circuit belonging to the invention,
and
Figs. 3 and 4 show the ramp in reduced scale and at two different water levels.
[0008] In the figures, 10 refers to a quay and 11 in its entirety to a loading and off-loading
ramp for vehicular goods and which is anchored to the quay and has a pontoon float.
The ramp 11 is connected to the quay edge via a horizontal pivot 12, which is elastically
mounted in the quay structure via fender means 13. The pivot 12 and fender 13 are
bridged by a flap 14. The port ramp 11 comprises a pontoon float 15 and a vertically
pivotably mounted ramp bridge 11a, which is principally equally supported by the quay
and the pontoon float 15, and bridges the distance between these. This distance which
is equal to the length of the ramp bridge 11a, is so chosen that the gradient of the
ramp bridge is not too steep, even during extreme tidal conditions.
[0009] The quay 10 preferably forms, which is not shown in the figures, a L-shaped angle
and is equipped with mooring means for the pontoon float 15.
[0010] At a conventional port ramp of this kind the pontoon float 15 tend to trim (pivot
about its centre of floatation) when a terminal truck 17 moves onto it from a ship
18. This trimming moment complicates the transfer of cargo into or from the ship 18.
[0011] In order to avoid this trimming, the port ramp 11 according to the invention is
equipped with damping means in the form of hydraulic piston cylinders 19 who are pivotably
mounted with one end in the ramp bridge 11a and the other in the pontoon float 15,
respectively. The piston cylinders 19 are connected to a hydraulic system shown in
fig. 2, which is so arranged that it facilitates a certain bleed of hydraulic fluid
between both fluid chambers 19a, 19b of each piston cylinder, i.e. from one side of
the piston 19c to the other side. This bleed of fluid is so adjusted that the port
ramp 11 can adapt its float level to the normal variations in water level, e.g. caused
by the tides. However, during the much more rapid development occuring when a terminal
truck 17 passes over the pontoon float 15, only a small amount of hydraulic fluid
will have time to pass from one fluid chamber to the other, so that the bridge ramp
11a and the pontoon float 15 will cooperate as a rigid unit having its pivoting axis
in the pivot 12 at the quay edge. This means that the total waterline area of the
pontoon float will be influenced under load and therefore utilized, resulting in
that the pontoon float 15 may be constructed smaller and less costly than in prior
art constructions of this kind.
[0012] The hydraulic system shown in fig. 2 comprises check valves 20. Further, there are
cut-off valves 21 allowing locking or insulation of some part of the system, i.e.
for exchange of some component. Connection pieces 22 are mounted in the system allowing
connection, e.g. of a hand pump into any part of the system. Nonreturn valves 23 are
mounted in parallel with the check valves 20 to avoid resistance on the suction side
of the piston 19c. Both piston cylinders 19 are connected to a mutual reservoir 24
containing hydraulic fluid and a rubber bladder 25 which communicates with the external
atmosphere. The complete hydraulic system is normally pressure free and thus only
acts to dampen the movements of the hydraulic pistons.
[0013] Figs. 3 and 4 show the port ramp 11 in two different extreme water level conditions
wherein the pontoon float 15 maintains its parallel trim in relation to the water
surface. Since the drive surface of the pontoon float 15 thus in unloaded condition
always is parallel to the water surface, the transit of a terminal truck between the
ship and the pontoon float is facilitated regardless of the float level of the ship
in relation to the pontoon float.
[0014] The above described and disclosed embodiment is only one example of the invention
and the details of it may be altered in several ways within the scope of the appendant
claims. For example, the damping means 19 may be differently designed and in different
ways connected to the ramp bridge and the pontoon float. The check valves 20 may be
adjustable for different load conditions.
A port ramp having a pontoon float, and forming a connecting path between a roll-on/roll-off
ship and a quay (10) in a harbour installation being subjected to variations in water
level, and wherein a ramp bridge (11a) is vertically pivotably connected to the edge
of the quay and to the pontoon (15) respectively, characterized in, that at least one hydraulic cylinder (19) is pivotably mounted between the ramp
bridge (11a) and the pontoon float (15), that both hydraulic cylinder (19) fluid chambers
(19a, 19b) are interconnected via at least one check valve (20) and connected to a
fluid reservoir (24), in order to slow down the speed of pivot angle variations between
the ramp bridge (11a) and the pontoon float (15), so that those together form an
interconnected, rigid unit in relation to the load produced by vehicles intermittently
moving over the pontoon float (15), as well as independently pivotable units in relation
to the action of variations in water level, e.g. caused by the tides.