SHELL 



shell— The hard outer covering of an inverte- 

 brate; a calcareous, siliceous, bony, horny, or 

 chitinous covering. 



shellfish— Any aquatic invertebrate with a hard 

 external covering, but more commonly any 

 crustacean or mollusk, especially the edible 

 commercial species. 



shell ice— (also called cat ice). Ice, on a body 

 of water, that remains as an unbroken surface 

 when the water level drops so that a cavity is 

 formed between the water surface and the ice. 



(5) 

 shingle— Rounded, often flat waterwom rock fra- 

 ments larger than approximately 16 milli- 



shingle barchanes— Eidges of shingle, with in- 

 tervening troughs of sand, formed in shallow 

 water at right angles to the beach. 

 shingle rampart— A ridge of shingle, about 3 to 

 6 feet ( 1 to 2 meters) high, built by waves on the 

 seaward edge of and parallel to a reef flat. (2) 

 shipboard synoptic system — Electronic ship- 

 board system (hove-to) that collects, records, 

 and prepares for radio transmission the profile 

 of temperature, salinity, and sound velocity with 

 depth. 

 shipborne expendable bathythermograph (BT) 

 — An instrument system designed to record 

 water temperature with depth from a ship mov- 

 ing at speeds up to 25 knots in sea states up to 

 6 (13 to 20 feet) without interference to normal 

 ship routine. It can provide measurements 

 from surface to 1,500 feet with an accuracy of 

 ±2 percent or 15 feet whichever is greater and a 

 temperature accuracy of ±:0.4°F over a range 

 of28°to95°F. 

 ship motion — In perfectly calm water a carefully 

 steered ship moves along a straight course. A 

 point which corresponds to the center of gravity 

 of the ship also moves along this straight line 

 at a constant velocity. In a wave system, how- 

 ever, this point deviates from this simple, 

 straight line motion in six different ways: 



1). Heave, the up-and-down motion of this 

 point as it travels along. 



2). Surge, the fore-and-aft motion of this 

 point as the ship speeds up and slows down 

 when she encounters waves. 



3). Sway, the athwartship motion as the 

 point departs from a straight line path. 



4). Roll, the athwartsliips angular rotation 

 about this point whicli occurs as the ship heels 

 first to one side and then to the other. 



5). Pitch, the fore-and-aft angular rotation 

 about this point which occurs as the bow and 

 stern alternately rise and fall. 



6). Yaw, the horizontal angular rotation 

 about tliis point which occurs as tlie direction of 

 the ship's keel is deflected from tlie direction 

 of her course. 



The first three motions are translational mo- 

 tions, the last three are rotational motions. In 



other words, the first three motions are motions 

 such that the center of gravity actually departs 

 from its straight line motion and the last three 

 motions are motions such that the center of grav- 

 ity does not depart from its position. 

 (46) 



ship observations — ^Meteorological and oceano- 

 graphic data taken for a specific location, ob- 

 served from a ship underway or at anchor. 



ship report — The encoded and transmitted report 

 of a marine weather observation. (5) 



ship synoptic code — A synoptic code for com- 

 municating marme weather observations. It is 

 a modification of the International Synoptic 

 Code. (5) 



Ship Visit Report — A navigational report sub- 

 mitted by ship's personnel. In addition to data 

 affecting the safety of navigation, the reports 

 involve such intelligence as marine and celestial 

 phenomena, weather routing, current data, etc. 



shipworm — (or Teredo). One of a family (Ter- 

 edinidae) of wormlike bivalves in which the 

 shells are limited to the head end. Larvae pene- 

 trate wood, plastics, and other material, and the 

 organisms excavate tmmels (in which they re- 

 main for life) as they grow by rasping away 

 the surrounding material with their ridged and 

 toothed shells. Incurrent and excurrent siphons 

 project from the original entrance hole, which 

 is never enlarged. Ship worms are one of the 

 two most destructive groups of marine borers. 



shoal — 1. A submerged ridge, bank, or bar con- 

 sisting of or covered by unconsolidated sedi- 

 ments (mud, sand, gravel) which is at or near 

 enough to the water surface to constitute a dan- 

 ger to navigation. If composed of rock or 

 coral, it is called a reef. (An offshore hazard 

 to navigation with a least depth of 10 fathoms 

 (20 meters) or less, composed of unconsolidated 

 material.) (62) ^See reef. 



2. (or school). A great number of fish or 

 aquatic animals thronged together or con- 

 sidered as a group, for example, herring shoals. 



3. Having little depth; to cause to become 

 shallow. (61) 



4. To proceed from a greater to a lesser depth 

 of water. (61) 



5. To become shallow gradually. (61) 

 shoal area — 1. An area, dangerous to surface 



ships, in which there are depths of 10 fathoms, 

 or less, over a bottom which is not rocky. 

 2. A shallow area. 

 shoaling — A bottom effect which describes the 

 height of the waves, but not the direction. It 

 can be divided into two parts which occur 

 simultaneously. The one part has to do with 

 the fact that waves become less dispersive close 

 to shore; therefore, since the same energy can 

 be carried by high waves of lesser height, this 

 effect causes a gradual decrease in the wave 

 lieight. In the other part, the waves slow down. 



146 



