OCEANOGRAPHY AND THE MARINER 



conditions. Care is taken to avoid crossing of or sailing opposite 

 standard tracks. Shipmasters and commands have written many 

 comments regarding the ship routing programs. Besides the ad- 

 vantages of more economical operations and time savings, routing 

 programs reduce worry on the part of the shipmaster by alerting 

 him to forthcoming weather conditions. These programs also enable 

 greater utilization of new crews. 



Natural conditions and artificial methods exist for abating or 

 somewhat calming the high seas. The most important natural 

 abater is ice, which occurs only in higher latitudes. Hail, snow, and 

 seaweed also exert calming effects, though they are considerably less 

 than the effect of ice. Artificial methods of reducing wave height 

 include breakwaters and the distribution of storm oil. 



By measurement and analysis, oceanographers have shown the 

 sea surface to be a complex composed of many different wave trains 

 occurring simultaneously. Each of these trains has its own period, 

 height, length, and direction of travel. Waves are measured from 

 stationary platforms and along shores by means of electronic wave- 

 staffs, pressure diaphragms, radar, and with instruments similar to 

 tide gages. They can be measured from moving craft with sonic 

 siirface scanners, inverted echo sounders, and with accelerometer 

 devices. Floating electronic wavestaffs and expendable accelerom- 

 eter devices have been used successfully in open-ocean measurement 

 of waves. 



PHYSICAL PROPERTIES 



Until about a decade ago, physical oceanography was probably 

 one of the least understood science subjects. In general, its results 

 found most practical application in the solution of marine fisheries 

 problems. Therefore it was considered more of an adjunct to the 

 field of marine biology, and, for this reason, most of the earliest 

 advanced studies of physical oceanography stemmed from complex 

 investigations made by investigators more interested in the general 

 approach (classic oceanography). Specialized investigators were 

 interested in the geographic approach. More recently, physical 

 oceanography has evolved an aggi-egation of highly trained research- 

 ers, each a specialist in his own right. Because of the existence of 

 several similarities between oceanic and atmospheric problems, many 

 meteorologists have been inducted into and successfully adapted to 

 the field. 



Some of the more common physical properties of sea water are 

 temperature, salinity, density, pressure, ice, water color, transpar- 

 ency, and sound velocity. Less commonly known or determined ones 

 are specific heat, osmotic pressure, eddy viscosity, electrical conduc- 

 tivity, etc. Development of instrumentation for use in securing 

 measurements of the most common of these parameters has been 

 fairly rapid in recent years. The least common parameters are 

 usually determined by complex mathematical calculation and formu- 

 lation from one of a combination of the common parameters. 



Much greater improvement in future instrumentation will be 

 necessary before the study of physical oceanography can parallel the 

 pace of present-day meteorology. Original instrumentation, instru- 

 mentation in numbers, and the feasible means of utilizing this 

 instrumentation are needed before we will be capable of attaining 

 our desired degree of worldwide synoptic observations. 



Surface temperatures are obtained by the simple means of a 

 scientific mercury thermometer, the bulb of which is immersed in a 

 small attached container filled with sea water by submersion. Some 

 injection temperature values are reported as surface values. How- 

 ever, since they are taken at various depths at engineroom intakes 

 on ships, submarines, and offshore structures, they are unreliable for 

 precise oceanographic work. Continuous recording of temperature 

 for industrial research purposes is made with a thermograph. 



The present common method of obtaining deep sea temperature 

 data involves the use of paired specially constructed reversing ther- 

 mometers, one protected by enclosing it in a glass sheath and the 

 other unprotected. Through comparison of the two temperature 

 readings obtained after reversing the thermometers and application 

 of correction factors, one can readily determine the water tempera- 

 ture and correct depth at which the thermometers were actuated. 

 A bathythermogram is a record made with an instrument known as 

 a bathythermograph and consists of a continuous trace of tempera- 

 ture plotted against depth at a given location. BT's are collected 

 by naval and merchant vessels the world over and forwarded to the 

 Oceanographic Office for processing, use, and distribution. Hundreds 



of thousands have been collected and processed to date. However, 

 processing this type of data is very time-consuming. Serial vertical 

 temperature distribution values are also obtained by electronic 

 methods incorporating parallel -connected electrical resistors, the 

 values of which are directly dependent on water temperatures, e.g., 

 the thermistor chain and the thermocline recorder. The latter is an 

 improvement of the former in that the quantity of measurable resist- 

 ance change is greater. Resistance thermometers operate on this 

 same principle, however, they are not as sensitive as the thermistor 

 chain or thermocline recorder. 



Water temperatures have been obtained in the past with insulated 

 water bottles to depths of several hundred yards. Owing to the large 

 margin of error in this method, the reversing thermometer or ther- 

 mistor methods are preferred when measuring deep water temperatures. 



On the basis of considerable temperature data, charts have been 

 constructed to indicate survival rates for immersed bodies. 



Cargo temperature is dependent on temperature of the air and 

 sea water, particularly in instances of bulk liquids or highly porous 

 materials; passenger comfort is also to a degree dependent on air 

 temperature and thus indirectly on sea water temperature. Cargoes 

 with temperature values less than the dewpoint of the outside air 

 will suffer condensation damage if ventilated when such conditions 

 exist. In some cases, sea water temperature can either reduce endo- 

 thermic cargo reactions or, conversely, it can cause buildup of cargo 

 temperature. Cold spray or wash from stormy seas can reduce 

 weather deck temperatures sufficiently to produce condensation 

 within warm holds, thus abetting deterioration and waste of cargo. 



Salinity of sea water is based on the quantity of dissolved salts 

 contained in a given amount of sea water after certain chemical 

 changes have taken place. Direct determination of these values by 

 recommended procedure is rarely carried out at the present time, 

 because the method is too difficult and slow. Sea water composition 

 adheres to the Law of Constant Proportions, i.e., the total amount 

 of the major constituents in any two samples is always present in 

 the same relative proportions. Since chloride ions constitute more 

 than half of the total amount of chemicals in sea water, salinity 

 values can be empirically related to chlorinity once the latter has 

 been established by chemical means. A relationship also exists 

 between salinity and electrical conductivity values of sea water. 

 Based on this knowledge, an extremely complicated electronic 

 instrument has been developed and proven suitable for rapid pro- 

 cessing of salinity samples. However, the technical nature and 

 prohibitive cost of these machines have limited their distribution. 

 A smaller portable underwater version of this apparatus, the con- 

 ductivity cell, has been successfully used in many regional surveys. 

 By correlating water temperature and electrical conductivity values, 

 this instrument automatically furnishes the observer with immediate 

 values of salinity. 



Temperature values go hand-in-hand with salinity values to 

 determine the extent and growth rate of marine fouling in all areas 

 by controlling the environment in which the organisms must live. 

 Certain combinations of temperature and salinity values can be 

 highly conducive to corrosion of any type of structure. In particular, 

 equipment constantly bathed in sea water is susceptible to adverse 

 corrosive, contractive, or expansive damage. Condenser failure is 

 iisually due to corrosion of tubes and ferrules. 



Temperature and salinity also combine with pressure effects to 

 form the density values of sea water — values so important in calcu- 

 lating loadlines for freshwater to salt water transits and vice versa. 



Many cases of improper stowage have resulted in loss at sea or 

 serious listing after freshwater to salt water transits. Improper dis- 

 tribution of bulk cargo coupled with low-temperature conditions 

 have proven disastrous for ships in rough waters . Extra buoyancy 

 provided by empty fore and aft tanks and brittleness of metal pro- 

 duced by low temperatures have promoted cracking or complete 

 severance of tankers. 



Density of sea water is an important factor of economy in 

 evaporator operation; the lower the density, the less the amount of 

 fuel that is required. Density of surface water can be measured 

 directly with a hydrometer. However, since it increases with rise 

 in pressure and salinity and decreases with rise of temperature, it 

 can also be determined directly for water beneath the surface from 

 these latter values by use of oceanographic tables. 



Pressure can be used to measure sea and swell heights and periods. 



Currently, importance of the least investigated physical proper- 

 ties of sea water to the mariner is little understood. At best, the 



