Mooring or breasting structures are known in the maritime arts for guiding and securing vessels to a fixed location on a body of water for loading, unloading or storage. One particular type of mooring or breasting structure, known as a dolphin, consists of groups of elongate piles having a first end driven into the bed underlying the body of water and a second end extending above the body of water for contacting the vessel.
Ideally, in order to avoid damage to either the vessel or the dolphin upon a vessel impacting the dolphin, the dolphin must possess considerable powers of resistance and also a high degree of elasticity. Oberschulte, U.S. Pat. No. 1,837,998, is illustrative of one dolphin structure which attempts to provide the combination of resistance and a high degree of elasticity. Oberschulte teaches providing a plurality of vertical hollow metal piles which are interconnected at their lower ends along a length to be imbedded into the bed underlying a body of water. The remaining portion of the piles, which extend above the bed, are unconnected along their remaining length to provide a resilient structure above the bed for elastically opposing horizontal loads. Not only does such a structure help dissipate the energy of a vessel striking fenders surrounding the piles, but by having the piles unconnected "pull out forces" which might otherwise lead to pulling of the piles from the bed are avoided. However, the structure taught in Oberschulte fails to optimize energy dissipation.
The prior art has recognized that fender piles can be utilized as part of a mooring structure in order to help dissipate the force of an impact of a vessel. Illustrative fender structures are those shown in Peterson, U.S. Pat. No. 2,420,677;
Bergfelder, U.S. Pat. No. 4,919,572; and Julian et al, U.S. Statutory Invention Registration H402.
Peterson teaches a fender pile having a distal end rigidly embedded in a sea bed and a proximal end in abutment with a support structure such as a pier supported on a number of piles. Peterson further teaches providing shock absorbing springs at a select point along the length of the pile for allowing the pile to bend as a horizontal load is applied while preventing the pile from bending beyond its elastic limit.
Bergfelder teaches a prestressed concrete fender pile having a proximal end rigidly secured in a sea bed with a distal end abutting a pier or the like. The concrete fender pile is prestressed with high strength fiber prestressing elements which are resistant to the corrosive effects of water. Bergfelder teaches the fender pile as being able to dissipate energy by the pile bending in response to a horizontal load between the distal end and a point above the proximal end of the pile at around the level of the bed.
Julian teaches an energy absorbing prestressed concrete fender pile which includes a rubber fender or insert between the fender pile and the pier, but which otherwise dissipates energy by deflecting in the same manner as described above with regard to Bergfelder.
While each of these fender systems is somewhat effective in helping to dissipate energy which might ultimately have to be born by the pilings of a dolphin, they can result in high bending moments near the proximal end of the fender pile, which can lead to failure of the fender pile. None of these structures therefore present an optimal solution for dissipating horizontal loads.
Holly, Jr., U.S. Pat. No. 3,852,968, teaches providing cantilevered torque arms with bumpers at their distal ends attached to vertical steel piles. Impacts on the bumpers create torsion and bending forces in the piles to help dissipate energy of an impact. However, Holly requires that the vertical piles be secured against axial rotation at their base, which can be difficult and expensive to achieve. Thus, while making effective use of torsion to absorb a load, the structure taught in Holly is prohibitively expensive in many applications.
One additional known way to assist in the dissipation of energy and to protect a vessel and a fender from wearing from contact therebetween is to provide a bumper on the load impacting fender. Walker, U.S. Pat. No. 3,541,800; Leblanc, U.S. Pat. No. 4,411,556; Thomerson, U.S. Pat. No. 4,338,046; Sluys, U.S. Pat. No. 4,357,891; and Aks, U.S. Pat. No. 3,486,342, teach a number of bumper structures for use on a fender.
While each of the structures discussed above provides some teaching of energy dissipation for fender or dolphin structures, none of them teach an inexpensive, simple to construct dolphin structure which optimizes energy dissipation through the use of each element of the dolphin structure.
The present invention is directed toward overcoming one or more of the problems discussed above.