modules, lashed together, form a moored element. Alternate moored elements 

 are displaced seaward in a staggered (checkerboard) layout to facilitate moor- 

 ing. Each array of nine elements has an axial length of about 1,070 feet, and 

 an effective length of about 640 feet. 



In this concept the module is a barge which can be towed short distances, 

 carrying its complement of floats to the point of installation. It can also 

 be transported by various means over the ocean. Upon delivery to the site, 

 the floating modules can be immediately unloaded from the transport ship or 

 barge and temporarily stored at moorings or on the sea floor. Another feature 

 is a provision to refloat the module by introducing low-pressure air into 

 chambers in the structural members. The goals of versatility with respect to 

 transportation, installation, and retrieval time were approached through use 

 of the largest size preassembled units, which make handling less difficult for 

 naval operations. 



b. Concrete Articulated-Frame (Floating) Ballast Tethered-Float Break- 

 water . The Tethered Float Breakwater Ocean Experiment project in 1976 

 selected an articulated ballast concept from several design proposals from 

 private industry. A contract was awarded for the design of an articulated 

 framework of relatively small, triangular modules of reinforced concrete, 

 joined together with flexible connectors at their apexes (Fig. 122). The 

 modules are designed as equilateral triangles 20 feet on each side. The cross 

 section of the legs of the triangle is about 12 inches wide and 20 inches 

 deep. Float attachment points are located on the connectors and at the mid- 

 points of the sides. The triangular modules are designed to be assembled into 

 an articulated frame normally 100 feet wide; the length depends on the number 

 of rows of floats. The breakwater is composed of several of these large 

 assemblies. 



The width of a typical moored element containing 37 rows of floats would 

 be 312 feet. A staggered array of 19 moored elements would be a breakwater 

 with an overall axial length of 1,900 feet, which provides a 7-second break- 

 water with about 1,500 feet of effective length. The major features of this 

 concept include flexibility, obtained through numerous articulations, which 

 permits greater amplitudes in vertical motion of the ballast, eliminating 

 concern about extreme dynamic loads in the tethers. A consequence of the 

 flexible ballast concept is that components are small (the heaviest are the 

 6.5-ton triangles and the 0.5-ton trimming weights). Buoyancy is provided 

 only in the floats. Once assembled and placed in sufficiently deep water, a 

 moored element would be towed with the ballast submerged. 



c . Steel-Frame (Bottom-Resting) Ballast Tethered-Float Breakwater. In 

 1977 the Tethered Float Breakwater Ocean Experiment project developed a 

 bottom-resting system for about a 25-foot depth for installation at an ocean 

 site near San Diego, California. Preliminary performance analysis indicated 

 that cylindrical floats of relatively high density would be the most effi- 

 cient. The Naval Ocean Systems Center, San Diego, California, designed a 

 float made from scrap automobile tires with a ballast module compatible with 

 the float properties (Fig. 123). Two modules were installed in 1978. The 

 float is a stack of five or six used automobile tires filled with polyurethane 

 foam, with the top and bottom of the foam core capped with concrete. A steel 

 hook for connecting the tethers is embedded in the concrete. The float is 

 essentially a cylinder about 2 feet in diameter and 4 feet high, and weighs 

 about 475 pounds with a relative density of 0.56. 



177 



