3c 



the maximum force expected to occur. Since the forces are cyclic, all 

 the connections between the breakwater and anchor should be as flexible 

 and free-moving as possible. Therefore, it is suggested that either 

 galvanized steel or wrought-iron chain be used. Wire cable has been 

 used, but the cable is subject to both axial fatigue and corrosion 

 weakening. All connections should also be oversized to allow for cor- 

 rosion and wear. Secondary methods of connection, such as cotter pins 

 and extra nuts, should be used to prevent disconnection. 



2 . Selection of the Anchor . 



The selection of the type of anchor depends on the maximum mooring 

 force, bottom conditions (i.e., mud, sand, or rock bottom), and the var- 

 ious available methods for placing the anchor. The four basic anchor 

 types normally used with floating breakwaters are deadweight anchors, 

 embedment anchors, screw anchors, and pile anchors. 



The most commonly used anchor is the concrete block deadweight anchor 

 which is usually cast at the site. The design anchor weight (VL.) of 

 these anchors can be determined by the following relationship based on a 

 static analysis: 



F + F 



t r S 



(-£) 



(3) 



where 



y = the coefficient of static friction 



W. = the total weight of concrete anchor in air 



w^ = the unit of weight in water 



w = the unit weight of concrete 



F^ = the lateral mooring-line load 



Fa = the factor of safety 



The embedment anchor is often used by small-boat operators. The 

 holding capacity of embedment anchors vary with the type or marine soil 

 and embedment anchor design. This is discussed by Taylor and Lee (1972) 

 and Berteaux (1976) . 



Vesic (1971) and Jenkins (1976) describe methods for determining the 

 holding capacity of the screw anchor in various soil types. They indi- 

 cate that the maximum holding capacity is equivalent to the capacity 

 developed by a short pile of equal length. Disadvantages of the screw 

 anchor are that they usually have a short length and are difficult to 

 install in firm marine soils. 



13 



