Various types of prior art artificial reef systems have been placed on the ocean floor in the vicinity of the shore to prevent beach erosion. In these known systems a principle purpose is to provide a subsurface breakwater structure for deflecting water currents and thereby reduce the damaging force of the waves as they impact on the beach. Another purpose is to provide a structure that has the characteristics of a natural reef and thus is attractive and protective of fish and aquatic organisms. In the case of a breakwater, waves passing over the subsurface structure break a sufficient distance off shore to reduce the energy carried by the waves as they continue on toward the shore. As a result, the speed is diminished and sand carried by the water is permitted to be deposited on the beach rather than being removed by undertow, i.e., the reverse underwater current caused by receding waves.
Examples of prior art artificial reefs are shown in U.S. Pat. No. 5,102,257, issued on Apr. 2, 1992 to Richard E. Creter, and U.S. Pat. No. 2,069,715, issued on Feb. 2, 1937 to John B. Arpin. These reefs utilize reinforced concrete modules having a triangular prismatic shape, placed in side-by-side fashion and coupled together to form a submerged breakwater. The Creter reef module weighs about 12 tons when constructed to the dimensions disclosed in the patent. Other similarly shaped artificial reef modules constructed from reinforced concrete have been known to weigh 20 tons.
Another known arrangement for providing an artificial reef is the use of a pliant bag filled with water and submerged off shore, as disclosed in U.S. Pat. No. 4,958,956, issued Sep. 25, 1990 in the name of Massahiro Tanaka, et al. Because the bag is resilient it deforms as waves pass over it and part of the wave energy is dissipated which in turn is claimed to reduce wave size.
An artificial ocean reef utilizing modules with a general dome shaped configuration on a steel reinforced slab is shown in U.S. Pat. No. 5,215,406, issued Jun. 1, 1993 in the name of J. Harold Hudson. These modules in the preferred embodiment are formed from concrete and have a hemispherical shape with access ports for creating water flow to mimic a natural reef.
The use of corrugated plates made of flexible material such as polyethylene held on frames suitably placed on the ocean floor is also disclosed in the prior art. U.S. Pat. No. 4,171,174, issued Oct. 16, 1979 in the name of Ole J. F. Larsen shows several embodiments of artificial reefs in which this principle is embraced.
Many of the known artificial reefs used as submerged breakwaters to protect against beach erosion comprise structure that is difficult and costly to fabricate, transport and install. For example, in one application a series of prefabricated concrete modules are used, each of which weighs as much as 20 tons. This massive structure not only contributes to the cost but also requires significant amounts of labor in the production as well as the installation of such modules in the submerged operational environment on the ocean floor. Bulky cumbersome objects of this nature are inherently difficult to handle and transport as well as maintain due to the magnitude of their weight. These problems become even more pronounced in view of the undersea water currents usually prevalent in the off shore environs in which breakwaters are installed and maintained.