OCEANOGRAPHY AND THE MARINER 



Tides are measured visually and mechanically with staffs and 

 gages at numerous coastal stations throughout the world. In certain 

 areas, they have been measured in open waters, e.g., stable platforms 

 located on shoals in the Atlantic Ocean and the Gulf of Mexico. 

 Measurements of sea level changes with precise surveying instru- 

 ments have revealed tidal components with periods greater than 

 those normally perceptible by human, mechanical, or electronic 

 means. A tautly anchored spar buoy has been used as an experi- 

 mental visual staff in the Gulf of Mexico. However, inherent 

 problems due to wind and current drag preclude the use of this 

 method in place of more precise measuring equipment. A variety 

 of glass capillary tubes has been used to measure tides in private 

 research projects. 



The importance of tides and currents to the mariner cannot be 

 overemphasized. In areas where these factors exert their greatest 

 influences, ship's officers should familiarize themselves with out- 

 standing oceanographic factors. Many ships have suffered damage 

 ranging from slight to heavy or have become total losses owing 

 to a lack of tidal knowledge. Good seamanship demands use of 

 up-to-date nautical charts and publications together with full com- 

 prehension of their meaning. 



One might think of the great ocean currents as being nothing 

 more than great rivers of the sea since their lateral limits are rela- 

 tively well defined. However, general ocean currents have neither 

 beginning nor end and thus result in the formation of clockwise 

 patterns in Northern Hemisphere oceans and counterclockwise pat- 

 terns in Southern Hemisphere oceans. General ocean currents are 

 the most important controllers of climatic conditions over land areas, 

 and have become important factors in meteorological studies. 

 Thermal and chemical concentrate changes in seawater are brought 

 about by freezing, evaporation, heating, and precipitation; the first 

 two factors increase the density of sea water, while the last two 

 decrease its density. 



Theoretically then, one would expect the more dense polar 

 waters to sink and replace the less dense equatorial waters which 

 would flow poleward on the ocean surface. This condition would 

 produce simplified ocean current patterns which could readily be 

 understood and predicted. However, the actual current pattern is 

 made complicated by the effects of wind and rotation of the earth 

 (Coriolis force). Ocean currents are the dynamic result of unbal- 

 anced physical conditions tending to right themselves in the direction 

 of equalization. 



Navigational safety took a great turn after the sinking of the 

 TITANIC in 1912. Formation of the International Ice Patrol led 

 to collection of varied data such as temperature, current, ice drift, 

 and bathymetry in the North Atlantic. Benefits derived from the 

 many seasons that the Patrol has operated include the prediction of 

 ice limits and conditions not only for the safety of ships transiting 

 regular shipping lanes in higher latitudes but also the ice-transits of 

 supply and research ships in extreme latitudes. Since the greater 

 part of an iceberg or floe is submerged, the ocean currents are a 

 greater determinant of direction and speed of drift than is the wind 

 influence. Oceanographic ice forecasts have led to many successful 

 convoy transits through icebound waters and have undoubtedly 

 reduced ship damage and loss. 



This aerial photograph shows the "calving" of icebergs 

 from the Antarctic ice sheet 



Project Polynya conducted at Thule Harbor in Greenland has 

 been successful in producing artificial water currents at dockside. 

 Compressed air is distributed through the water from perforated 

 tubes lying on the harbor floor. Lengthening the shipping season 

 by direct application of dynamic principles is of primary concern in 

 this experiment. 



Many harbors, being located near or in river mouths, are 

 subject to heavy silting due to currents. Silting rates for dredging 

 purposes have been determined by oceanographic research projects 

 in many areas. Knowledge of silting, erosion, and current rates is 

 indispensable for the planning of breakwaters, piers, lighthouses, and 

 also various types of oceanic construction. 



Currents are an important factor in the distribution of bio- 

 logical organisms, determining the quantity and area of shell and egg 

 deposition. Transportation of nutrients and plankton vital to the 

 majority of life in the sea is provided by currents, thus determining 

 which areas of the oceans will become commercially important. 

 Marine fouling growth rates also are regulated by the distribution 

 of these nutrients as well as by physical properties of sea water. 



General surface current charts and some detailed information 

 concerning local currents are provided in the Sailing Directions pub- 

 lished by the Oceanographic Office. These publications also provide 

 corange and cotidal line charts, i.e., charts which show lines con- 

 necting points having equal heights and times, respectively, of tides 

 in any given area. All recent editions of Sailing Directions include a 

 rather comprehensive section on the subject of general oceanography 

 for the particular area covered by the publication. 



SEA AND SWELL 



Of all oceanographic parameters, probably the most familiar to 

 sailors are sea and swell. According to definition, "sea" is composed 

 of waves generated by local winds. These waves are relatively short 

 in period and generally advance in the same direction as the wind. 

 "Swell" consists of ocean waves which have advanced beyond the 

 area of their generation. 



Neither of these parameters serves the mariner beneficially, 

 rather they are adverse under most conditions. Sea and swell 

 coupled with intense cyclonic winds are definitely a great cause of 

 severe damage to shipping and loss of life. Fire and explosion 

 damage, sometimes attributed to direct effects of rough seas, also 

 have been correlated with atmospheric thermal conditions. Other 

 forms of meteorological disturbances such as hurricanes and water- 

 spouts are responsible for more damage incurred by ships at sea. 



Waterspout damage is caused by a combination of tornadic 

 winds, suddenly reduced atmospheric pressure, and the deluge of 

 water sometimes released. Although the funnel of a normal water- 

 spout is composed of small water droplets formed by condensation 

 from cooling due to atmospheric pressure reduction, it is believed 

 that the more severe storm spouts carry considerable quantities of 

 sea water up to fair heights. 



Lack of knowledge concerning the structure and properties of 

 waves and swell has been an obstacle to theoretical and practical 

 applications of oceanography in the reduction of ship motions, a 

 desirable goal for all oceangoing vessels. Benefits to be derived 

 from such studies include improvement of speed, cargo safety, pas- 

 senger comfort, and reduction of ship damage. 



Each vessel will respond more violently to waves of certain 

 periods, since this is a function of ship dimensions and center of 

 gravity. When a ship encounters such wave conditions there is 

 little that can be done to alleviate the magnitude of the stress and 

 strain forces, outside of attempting to ease the ship's headway by 

 speed reduction, by change of course, or by altering trim. Structural 

 failures are apt to occur and, theoretically, ships have disappeared 

 without a trace under such circumstances, especially when carrying 

 extremely light or heavy cargoes while subject to pounding. 



The first organized attempts at overcoming hazardous ocean 

 conditions were made by Maury in 1847 by gathering ship logs and 

 collecting oceanographic data. With assemblage of these data in 

 the forms of wind and current charts, the mariner was provided with 

 the means to avoid hazardous areas and to follow best tracks. 



By 1961, at least several commercial companies and two govern- 

 ment units predicted best routes for the mariner. Experimental 

 routing has been conducted by the Oceanographic Office since 1956. 

 Depending on the individual ship requirements, the predictors aim 

 is to forecast either a least-time track, a maximum passenger comfort 

 track, a maximum cargo safety track, or any combination of these 



