Material or article handling – Marine loading or unloading system
Reexamination Certificate
2002-10-02
2004-11-02
Hess, Douglas (Department: 3651)
Material or article handling
Marine loading or unloading system
C414S137900, C414S139500
Reexamination Certificate
active
06811368
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
Description of Attached Appendix
Not Applicable
BACKGROUND OF THE INVENTION
This invention relates generally to the field of loading ramps for ships and more specifically to a roll-on/roll-off system and process for equipment transfer between ships or a ship and quay.
Bridges, ramps and trusses have been used for millennia and constitute a mature field of engineering. New designs have evolved as new applications have arisen, larger spans have been required, it has been necessary to carry heavier weight or new materials have become available. New materials and assembly processes have led to changes in design producing larger, stronger and lighter structures. The weight of a bridge or ramp is important because it can be a significant proportion of the total weight that must be supported.
One emerging application is for a ramp spanning two platforms that may be moving about fixed points. Examples are between two ships, between a ship and a quay or between deep-sea oil rig platforms. Such ramps have been used in so-called roll-on/roll-off ships. When deployed these ramps allow a container to be driven directly between a ship and a quay. In military applications very heavy equipment such as tanks may be loaded or unloaded in this way.
As ships become larger there are many instances when they must be offloaded in deep water onto smaller ships in order to transfer their cargo to port. Military equipment may need to be offloaded where no port is available. In these situations the swell can cause substantial motion, especially in the smaller ship, making roll-on/roll-off cargo transfer impossible in all but the most benign conditions. In addition, the weight of existing ramps, which typically are 30 meters or longer, limits the length of the span. Clearly there is a need for a roll-on/roll-off cargo transfer system that can accommodate the conditions that prevail in deep water. It is also clear that such a system should be lighter in weight than ramps currently in use.
A number of designs have been proposed for ramps or bridges allowing vehicles or passengers direct access to a ship or floating platform. Most of these use one or more rigid ramps attached with hinges to accommodate some types of motion between the two ends. Hetmanski (“Ramp engagement device”, U.S. Pat. No. 3,735,440-1973) teaches the design of one type of hinge that allows a rigid ramp to pivot and disengage when necessary. Kummerman (“Movable access ramp for vehicles”, U.S. Pat. No. 3,846,860-1974), Vulovic (“Loading ramp securing system”, U.S. Pat. No. 3,971,090-1976) and Vulovic (“Ship loading ramp”, U.S. Pat. No. 4,043,288-1977) use horizontally hinged, rigid ramp sections to accommodate the difference in height between a quay and a ship's cargo deck allowing for changes due to tides or loading. Rolling is also accommodated. In all three of these patents one or both ends of the ramps may slide. While this may allow some slight fore-and-aft, lateral, or skew motions of the ship the range of motion is extremely limited.
Mori et al (“Slidable mobile bridge”, U.S. Pat. No. 3,715,769-1973) teaches means to position a ramp vertically and horizontally relative to a ship. The positioning means is then disengaged from the ramp which simply rests on the ship and quay. Again, this allows only a limited range of motion between ship and quayside.
Subsequent inventors added ball-joints to some ramp sections to allow greater freedom of movement. Stress was also reduced in these designs since ball-joints transmit no moments. Serrano (“Footbridge for connection between a fixed installation and an oscillating installation”, U.S. Pat. No. 4,162,551-1979) describes a permanent bridge with a rotating platform at one end and a platform supported on a ball-joint at the other. Three hinged, rigid sections are used to connect these platforms. Six degrees-of-freedom are accommodated with this design, however, the two end sections must have an acute angle from horizontal in order to allow lateral movement. This angle makes it impossible for such as structure to be used for vehicles in roll-on, roll-off applications. Wipkink et al adopted a similar approach (“Connecting bridge for personnel to connect two mutually movable marine structures”, U.S. Pat. No. 4,169,296-1979). Two sections were used and an additional pivot, with a vertical axis, was provided between the sections. This patent has no teaching regarding the angle of the ramp sections from the horizontal. If these sections are nearly horizontal, as would be desired for traversal by vehicles, lateral movement could not be accommodated.
Lucien (“Ramp apparatus”, U.S. Pat. No. 4,581,784-1986) uses a single rigid ramp section with a gimbal at one end and roller at the other to accommodate relative movement. It would be difficult for vehicles to traverse the gimballed end of the ramp where rapid, extreme motions would occur.
In Rawdon et al (“Hinged cargo ramp”, U.S. Pat. No. 5,253,381-1993) two ramp sections are horizontally pivoted with an additional pivot, between the ramp sections, that is oriented in the longitudinal direction. Only a limited number of degrees of freedom can be accommodated.
Kane et al specifically address roll-on, roll-off applications (“Ramp junction”, U.S. Pat. No. 5,359,746-1994). A rigid ramp is fixed to a quay by a kingpin, allowing certain degrees of freedom, and to a floating platform by sliding feet. The range of motion that may be accommodated is intentionally limited by shackles.
Sekiguchi et al (“Ship weight cargo loading and unloading system”, U.S. Pat. No. 5,511,922-1996) deal with the problem of matching the motion at the end of a ramp to a stationary deck. Vehicles are carried on a lift table that can tilt about two axes to match movement of the ramp. Castelli et al also deal with this problem (“Dynamic ramp interface system”, U.S. Pat. No. 6,192,541-2001). A platform is disposed between two ramps that can accommodate rotations about two horizontal axes. The end of each ramp is provided with “fingers” that form the transition between each ramp and the platform. Although this is claimed to be useful in high sea states the transition between rigid ramp sections is still made over only a relatively short portion of the ramp's length.
All of the aforementioned structures share a common feature: the ramp is composed of rigid sections and relative motion, where it is allowed, is concentrated at specific points. This is undesirable for roll-on, roll-off applications where the range of motion may be large, such as in high sea-states. Stresses, especially dynamic stresses, are extremely high at the points where the ramp is attached.
Streeter et al (“Method and apparatus for connecting a passenger boarding bridge to a movable body”, U.S. Pat. No. 5,950,266-1999) address the problem of positioning a ramp in a passenger boarding bridge such as is widely used in air and ferry terminals. They provide a system of sensors that control the movement of the passenger bridge in order to maintain a constant attitude of a bridging ramp. While this can accommodate small amplitude motions the size and mass of the passenger bridge make it impossible to reach large amplitudes and velocities.
Three patents teach the use of a flexible ramp for connecting movable platforms. Fisher (“Flexible staging platform and the like”, U.S. Pat. No. 3,994,036-1976), Ryan (“Combined marine ramp transfer and mooring system”, U.S. Pat. No. 4,003,473-1977) and McLain (“Articulated bridge”, U.S. Pat. No. 6,292,968-2001) teach the use of ramps or bridges that can flex to accommodate displacements at the ends as well as rotations about the vertical axes. Stresses at the mounting points are greatly reduced by this flexure. All of these structures are, however, designed for light loads or short spans. The extra strength that would be required for roll-on, roll-off applications would necessitate stiffening of these structures, reducing their ability to deform a
Blank Basil Eric
Deyhim Alexander Khosro
Advanced Design Consulting USA, Inc.
Hess Douglas
Schneiderman Anne M.
LandOfFree
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