Ch. 35] OPERATION OF NAVAL VESSELS 659 



lation, therefore, is a smooth sand where there is little movement; for 

 cables, a mud or sand bottom is preferable to other types. 



Shore Problems 



The stability of beaches and harbors, which affect shore installations 

 such as piers, jetties, groins, and temporary and permanent docking 

 facilities, have been treated in Chapter 15 of this symposium and will 

 not be discussed here. Additional shore problems, however, occur in 

 amphibious operations (Seiwell, 1946). These are of two types: the 

 effects on landing craft, and the trafficability of the beach. The suc- 

 cessful navigation of landing craft through the breaker zone to the 

 beach is not an easy problem, and different techniques may be required 

 under different conditions. Studies made during World War II showed 

 that the factors involved are the angle of approach, size, breaking 

 point, and type of waves, and the topography of the beach and im- 

 mediate offshore area. Coordinated oceanographic and sediment stu- 

 dies are thus required to determine the relative importance of the 

 factors involved and the manner in which conditions change with time. 

 The factors that affect the trafficability of a beach are less well-known. 

 The size and shape, and the size and shape distribution of the particles, 

 which affect permeability, porosity, compaction, and bedding, are 

 known to be important, as are the variations in tide and wave levels 

 and the slope of the beach, which affect drainage and air entrapment 

 (Emery, 1945). Possibly the angle of wave approach and the types 

 of waves may also be a factor. 



Operation of Naval Vessels 



Two applications of submarine geology and sedimentation to the 

 operation of naval vessels are evident. First, detailed topographic 

 maps of the bottom, in areas of some topographic relief, can be used 

 for navigation (Shepard, 1948). The bottom profile along the course 

 traversed by the ship may be matched to the map and the corrected 

 course and location thus obtained. Second, submarines frequently find 

 it necessary to lie on the bottom, either to effect repairs or to avoid 

 detection. At such times the firmness and topography of the bottom 

 are obviously of importance. In warfare, the camouflage character- 

 istics of the bottom may also be important, as a submarine in enemy 

 waters must avoid detection from the air. It may also make use of 

 the acoustic properties of the bottom to evade detection or hinder 

 tracking. A rocky bottom in shallow water will not only hamper the 

 enemy in an echo-ranging search because of the high reverberation, 

 but also may provide colonies of snapping shrimp which will con- 



