Marine landing structure with omni directional energy absorbing characteristics

A shock absorbing boat landing (10) is provided for attachment to a marine structure (14) such as an offshore platform or the like. The system (10) has a landing frame (16) which is supported by two pairs of upper and lower shock cells (22a and 22b). The landing frame (16) is pivotally coupled at (40 and 42) to the operative arms (26) of the shock element so that relative rotation between the operative arm (26) of the shock cells and the frame (16) can occur about a vertically extending axis whereby improved shock absorbing characteristics can be obtained.

TECHNICAL FIELD 
The present invention relates to boat and barge landing assemblies for 
attachment to marine structures to protect the structures from damage from 
contact with vessels such as barges and boats and the like, and in 
particular to a boat landing assembly for attachment to a marine structure 
wherein the boat landing assembly is provided with means for absorbing 
shock efficiently in not only the normal but also lateral directions. 
BACKGROUND ART 
In the production of the worlds petroleum reserves it has been a practice 
to erect offshore platforms from which drilling and production of these 
petroleum products can be accomplished. To service these platforms, 
vessels such as boats and barges are used to transport men and material to 
and from these platforms. When loading and unloading equipment, it has 
been necessary to dock these vessels against the platforms to unload 
equipment and supplies. It has also been a practice in the past to 
construct boat landings on these marine structures adjacent to the water 
levels for use in docking these vessels at the platform. These boat 
landing assemblies have been designed to protect the platform and the 
vessel from damage due to collision between the vessel and the platform. 
In some instances, boat landings have been provided with shock or energy 
absorbing devices to assist in preventing damage from collision. 
As the need for petroleum products is increased, offshore drilling and 
production of the world's reserves has moved from the shallower areas of 
the Gulf of Mexico where mild climates are present to deeper waters such 
as the North Sea where severe climates create enormous wind and wave 
forces on vessels servicing the platform. Prior art boat landings designed 
for shallow waters and mild climates have not provided the required energy 
absorbing characteristics in all directions of normal loading during the 
use of these assemblies. 
An example of a prior art boat landing is shown in the U.S. Pat. No. 
3,937,170, entitled "Bumper Guard and Arrangement for Water Covered 
Areas." This boat landing system consists of a rigid metallic frame with a 
plurality of resilient strips mounted on the exposed surface thereof to 
contact the vessel. It is important to note that the entire assembly is 
rigidly welded to the legs of the platform, and the energy absorbing 
characteristics of the system are accomplished through compression of the 
rubber strips thereon. 
Another example is found in the United States Pat. No. 4,058,984, entitled 
"Marine Cushioning Unit." This patent discloses a boat landing structure 
coupled to the platform through a plurality of shock mounts. This system 
provides good shock absorbing characteristics in a direction normal to the 
face of the boat landing structure but, because of the location of the 
element 16, lateral components of shock are not efficiently absorbed 
because of the necessity of compressing a shock element 16 to absorb 
lateral shocks. Therefore, this system does not accommodate lateral 
loading on the landing structure. 
Another prior art bumper system which does not absorb shock loads in the 
lateral direction is shown in U.S. Pat. No. 3,933,111, entitled "Dock 
Bumper Unit." In this system, the presence of shock loading on the bumper 
system by forces applied normal to the surface of the bumper is 
recognized. However, the patent teaches that lateral displacement of the 
bumper relative to the pier in response to components of dynamic forces 
exerted parallel to the bumper is rigidly restrained at all times. This is 
achieved by use of vertically inclined counter elements which exert 
generally lateral tensile forces between the bumper and the pier. Thus, 
the system of this patent does not provide an energy absorbing function 
for forces which are applied in the direction other than normal to the 
face of the bumper system. This structure rather than solving the problems 
of lateral loading suggests a structure which provides no shock absorbing 
characteristics in a direction lateral to the bumper. 
Another system is shown in U.S. Pat. No. 3,564,858 and is entitled "Boat 
Landing for Offshore Structure." In this patent the landing system 
illustrated is connected to the platform by upper and lower elements. The 
upper elements appear to be the major shock absorbing element of the 
system. It also appears that the upper shock absorbing element has no 
shock absorbing characteristics in directions parallel or lateral to the 
face of the fender assembly. The plunger of the shock absorber, however, 
does function to pivotally connect the shock absorbing element through a 
pin joint or the like to the fender assembly. It appears, however, that 
this pivot in the arrangement lies in a horizontal axis and does not 
provide for absorption of shock loads applied in a lateral direction. 
Another prior art system for protecting marine structures is shown in the 
pending Application Ser. No. 845,111, filed Oct. 25, 1977, and now 
abandoned. In this system, a boat landing structure is supported at its 
ends by upper and lower shock cells. The operative element of which is 
welded to the boat landing thus preventing relative movement between the 
shock cell and the boat landing. If lateral loads are applied to the 
system, the shock must be taken up in compression of the resilient element 
in the shock cell thus preventing any substantial lateral shock absorbing 
characteristics in the system. 
Although these prior art bumper systems are representative of the systems 
currently in use and have proved satisfactory in some environments, they 
have not proved entirely satisfactory where the absorption of lateral 
loads or shocks is necessary. 
DISCLOSURE OF THE INVENTION 
A shock absorbing boat landing is provided for protecting a marine 
structure against excessive shock loads in directions not only normal to 
the face of the landing system but also in directions having lateral 
components parallel to the face of the landing system. The system utilizes 
a conventional boat landing frame which is coupled through a vertically 
extending axis to shock absorbing elements which have energy absorbing 
characteristics not only in a direction normal to the face of the landing 
system but also in torsion. 
In one embodiment, a pair of shock frames are supported from a platform by 
upper and lower shock cells. A boad landing is pivotally connected from 
the shock frame. The pivot provides movement about a vertical axis to 
allow vertical rotation between the boat landing frame and the shock 
frames. This allows the system to collapse while the shock cells absorb 
energy in a tortional mode when shock loads are applied to the system in a 
lateral direction.

DETAILED DESCRIPTION OF THE INVENTION 
For purposes of understanding the present invention, one embobiment of a 
marine landing structure incorporating the present invention will be 
described. In this description, reference will be made to the accompanying 
drawings. Throughout the description reference characters will be used to 
identify in the drawings various parts and elements of the system. These 
reference characters will be used throughout the description and in the 
various FIGURES of this patent to describe the same or corresponding 
parts. 
In FIGS. 1-3, the details of one embodiment of a marine landing structure 
incorporating the present invention is shown. For purposes of reference, 
the entire system is identified by reference numeral 10. The system 10 is 
shown attached to two legs 12 of a marine structure 14 such as an offshore 
platform, dock or the like. The system is rigidly attached to structure 14 
in a landing area or the like where vessels may come into contact with the 
structure. In the embodiment shown, the system 10 is located at the water 
level and protects legs 12 (and other portions of the structure 14 such as 
fluid conduits, cross braces and the like) from damage by collision with 
vessels such as boats and barges docking against or colliding with the 
structure 14. The marine landing system 10 of the present invention is of 
the type which has an outer facing contact surface up against which the 
vessels can contact. In addition as will be described herein, shock or 
energy absorbing devices are contained in the system 10 and are utilized 
to absorb energy applied to the frame. 
The system 10 has an array of metallic structural elements which are welded 
together to form a rigid elongated landing frame 16. Frame 16 can be 
constructed from various types of members and from various materials. In 
the illustrated embodiment, trusses are used in the design of the frame to 
add rigidity thereto. The outward facing surface 20 (surface facing away 
from the structure 14) provides a contact surface. In the embodiments 
shown, resilient facing is provided for the surface 20. It is understood 
that various designs, shapes, materials and fabrication techniques could 
be used to fabricate the landing frame 16, yet only being important that 
the frame be able to span the landing area and possess sufficient strength 
to withstand impacts from vessels. 
The frame 16 is supported from the legs 12 by two pairs of upper and two 
lower shock cell means 22a and 22b, respectively. These two pairs of shock 
cells are positioned at spaced locations on the structure and near the 
ends of the frame 16. As shown by example in FIG. 2, each of the cells 22a 
and 22b have an outer tubular arm 24 and an inner arm 26. These arms are 
partially telescoped along a horizontal extending axis. The outer arm 24 
of cell 22a is rigidly fixed to leg 12 by welding at a flange 28 provided 
on the arm 24 for that purpose. The outer arm 24 of the lower shock cell 
22b is rigidly clamped to the leg 12 by clamp assembly 30. It is to be 
understood that other methods of attaching the arms 24 to the legs 12 
could be used as dictated by the design considerations yet only being 
important that the arms 24 be securely and rigidly fixed to the leg 12. 
As can be seen in FIG. 3, a shock element 32 is positioned in the annular 
space between the arms 24 and 26. In the embodiment shown, element 32 is 
made from an elastomeric material and is bonded to the interior of arm 24 
and the exterior of arm 26. In addition a shear plate 33 such as described 
in U.S. Pat. No. 4,005,672 can be used. 
The outwardly extending ends of the arms 26 of each pair of cells 22a and 
22b are rigidly connected to a vertically extending shaft or support 
member 34. The arms 26 of cells 22a and 22b and support member 34 form 
rigid shock frames. In the embodiments shown, the arms 26 are rigidly 
fixed to the support by clamp assemblies 36, it being envisioned, of 
course, that other means of rigid attachment could be used such as welding 
or the like. 
In the embodiment shown, the support members 34 are shown extending through 
barge bumper elements 38 which can comprise a plurality of bumper rings 
such as shown in U.S. Pat. No. 4,005,672. 
According to a particular feature of the present invention, the landing 
frame 16 is connected to the support members 34 by means of upper and 
lower pivot joints 40 and 42, respectively. These pivot joints allow the 
frame 16 and members 34 to rotate with respect to each other about a 
vertical axis while preventing any other relative movement between the 
frame and members 34. Surprisingly this freedom to rotate about a vertical 
axis allows the system to more effectively function to absorb loads or 
shocks applied to the system from various directions. In the embodiments 
shown, these joints 40 and 42 comprise sleeves which are fixed to the 
frame 16 and are of a size and shape to fit around the outside of members 
34 and to rotate thereabout. The sleeves could, of course be split sleeves 
as shown in FIG. 2. By removing the rigid connection between the landing 
frame 16 and the shock elements and replacing it with a connection 
providing relative rotation only about a vertically extending axis, the 
system is allowed to collapse in some loading conditions and, contrary to 
what would be expected this lack of complete rigidity at the connection, 
improves rather than diminishes the shock or energy absorbing 
characteristics of the system. The advantages of this unorthodox departure 
from the conventional rigid connection between the elements of the system 
can best be appreciated by considering FIGS. 4-9. In FIGS. 4-6, the system 
is illustrated as a link diagram in various loading situations. In FIGS. 
7-9, the shock cell 22a is shown in various loading situations. 
In FIG. 4, the link diagram shows the system in plan view with the landing 
frame 16 shown as a single link coupled at 40 to the arms 26 to pivot 
about the vertical axis. (For purposes of this diagram, the support 34 has 
been eliminated since it merely comprises a member providing structural 
integrity for the system and support 34 is merely a rigid extension of arm 
26.) Arms 26 are resiliently coupled through shock elements 32 to arm 24. 
Each of the arms is in turn fixed to leg 12. For purposes of explanation 
only, the upper shock cells 22a are shown, but because of their location, 
the lower cells 22b would operate in a similar manner. 
For purposes of this explanation, forces or shock load having components 
solely in the direction normal to the contact surface 20 (and parallel to 
the axis of the shock cells) are shown in the FIGS. 1, 3, 5 and 7 as a 
vector and are identified as F.sub.N. In addition, forces and shock loads 
having components which are transverse to the contact surface 20 (and are 
not parallel to the axis of the shock cells) are shown in FIGS. 3, 6, 8 
and 9 as a vector and are identified as F.sub.L. 
In FIG. 4, the system is shown in its at rest or no load situation. In FIG. 
5, the system is shown with a normal load F.sub.N applied thereto. As can 
be seen, the shock cells 22a react as illustrated in FIG. 7 with a 
telescoping action occuring between arms 24 and 26 to deform the shock 
element 32. This is the classical manner in which shock cells have been 
used to absorb shock. 
In FIG. 6, the system is shown with a load having a lateral component 
F.sub.L. This lateral component causes the three bar linkage 26-16-26 to 
collapse as shown in FIG. 6. This collapsing occurs because of the extra 
degree of freedom present at the joint 40. This collapsing of the linkage 
also provides a surprising result, in that it allows the shock cells to 
deform by axial bending as is shown in FIG. 8. It has been found that this 
lateral deformation of the shock cell provides good shock or energy 
absorbing characteristic. 
If the system is fixed or rigid between links 16 and 26 (as has been the 
practice in the past), these improved energy absorbing characteristics 
would not be present. In FIG. 9, the shock cell 22a is shown with the 
lateral load F.sub.L applied but the connection between links 16 and 26 
rigidly fixed. This fixes the orientation of arm 26 and prevents it from 
rotating. All of the lateral forces are absorbed in compression and 
tension in the shock element 32 as it is deformed between the walls of the 
arms 24 and 26. The limited distance between these two elements causes a 
stiff or poor shock absorbing reaction to the lateral force F.sub.L. 
Thus, it has been surprisingly found that by providing an extra degree of 
freedom about a vertical axis in the coupling between the shock absorbing 
element and the boat landing frame both, the axial and tortional shock 
absorbing modes of the shock cell 28 (shown respectively in FIGS. 7 and 8) 
can be utilized to provide a boat landing system which is not 
directionally sensitive. This is accomplished by utilizing a system which 
collapses contrary to the prior thinking that system should be rigid and 
provides a system which has good shock absorbing characteristics in both 
lateral and normal directions. 
In the embodiments shown, the frame 16 is pivotally connected to the arm 26 
through the member 32. It is envisioned, of course, that this pivotal 
connection can be made directly where space permits by pivotally coupling 
and supporting the frame from the arm 26 itself. It is also envisioned 
that even though the embodiment illustrated shows the use of a bumper ring 
assembly, the system of the present invention could be utilized without 
the presence of the vertical support 34 or the elements 38. It only being 
important that sufficient structural integrity be provided to the system 
to allow that the axis of rotation of the frame with respect to the 
operative arm of the shock element to remain vertical to remain fixed in 
all other directions of relative movement. 
Although one embodiment of the present invention has been illustrated and 
other embodiments have been described in the foregoing Detailed 
Description, it will be understood that the invention is not limited to 
the embodiments described and is capable of numerous rearrangements, 
modifications, and substitutions within the scope of the invention as 
defined by the appended claims.