SEAWAY 



85 



position of long crested ones. In making fiiis super- 

 position, the air-pressure coefficient cannot be assumed 

 to remain constant. A short-crested wave form is ex- 

 pected to have a lower pressure coefficient than the long- 

 crested one. Jeffreys indicated a ratio of 1:2. This 

 feature appears to have been neglected by Miles, Section 

 4.5. The usual spectral definition of the energy j)er unit 

 sea area does not appear to be sufficient in questions of 

 energ}^ transfer from wind. It appears to be necessary 

 to consider the flow of energy, i.e., energy transport, 

 which occurs not only in down-wind but in oblique di- 

 rections as well. The mean transverse-energy flow can 

 be neglected in an infinitelj' wide fetch and uniform wind, 

 but becomes important in narrow fetches and in fetches 

 with wind-velocity gradient in the lateral direction. 



20 Wave Growth in Cyclonic Wind. In the projects 

 on energy transfer suggested in the foregoing, rectilinear 

 wind and predominating waves tra\-eling in wind direc- 

 tion were considered. The action of a cyclonic wind 

 should also be investigated. In this case, at each incre- 

 ment of the fetcii, new wind-generated waves appear 

 with dominating direction at an angle to the previously 

 generated waves. Also there is a lateral wind-velocity 

 gradient. The problem of the total wave-energy growth 

 and the wave-directional spectrum must be established 

 for this condition. The prol)lem presumably can be 

 approached by a suitable extension of any of the methods 

 listed under project 14). 



Wind-tunnel tests on pressure distributions on wave 

 models with oblique crest directions (both long and 

 short), needed to implement this project, were listed 

 under project 2). 



21 Experiments on Wave Growth in Cyclonic Wind. 

 Experiments with model-tank wave generation by 

 cyclonic wind are desirable in connection with project 

 20). The scale of experiments shcjuld be .sufficiently 

 large so that gravity waves can be generated and capil- 

 lary waves could be neglected. Cyclonic wind can be 

 provided by an upward suction through a bell-mouthed 

 duct placed at a suital)le cUstance above water. This is 

 to be supplemented by a few guide vanes or jets at the 

 outer periphery in order to initiate the spiral air flow. 

 This project can lie considered as an extension of Wiegel, 

 Snyder and Williams' (19.58) work. 



22 Additional Wave-Spectra Measurements. There 

 is a wide disparitj- among the various spectra discussed 

 in Section 6, both in regard to the indicated rates of wave 

 growth and in the ultimate wave characteristics. Addi- 

 tional ocean-wave measurements and analyses are recom- 

 mended, under ideal conditions corresponding clo.sely to 

 the conditions of spectrum formulation. The visual 

 observation-data analysis of Walden, Section 6.52 

 should be repeated using new w;ive data, instrumentally 

 measured and spectrally analyzed. This large project 

 requires, of course, prior completion of several lesser 

 projects to be outlined. 



23 Theory of Shipborne Wave Gage. At the time 

 of writing, Tucker's (11)526, 1956) shipborne wave gage 

 appears to be the most suitable for ocean-wave recording 



on weather-observation ships. A theoretical analysis of 

 its performance was given by Pierson (0-1957), and it 

 appears to the author that such errors as are unavoidable 

 are not important in the case of a small ship on large 

 waves. On the other hand, a theory of the relationship 

 between the water pressure at a submerged gage and the 

 wave height has heretofore been used only in a crude form 

 with a rule-of-thumb correction for imll interference. 

 Development of this theory to include a more accurate 

 evaluation of the hull-wave interference is recommended. 

 It is particularly important for the measurement of the 

 iiigh-frequency wave components. 



At the same time, the choice of the most favorable 

 position for the gage installation may be investigated. 

 In particular, proximity of the gage to bilge keels shovild 

 Ije guarded against. 



24 Calibration of Tucker's Gage installation on each 

 ship against an independent stantlard appears to be an 

 evident requirement. It has not heretofore been prac- 

 tical because of the lack of such a standard. The 

 problem may be solved by installing wave gages on 

 suitable oft'-shore structures (Texas Towers) against 

 which a ship's gage can be calibrated. 



25 Installation and Routine Use of Tucker's Gages 

 on all w('ath('r-obser\'ation ships is recommended. 



26 Shipborne Analyzing Equipment. In observa- 

 tions made heretofore with Tucker's gage, analysis of 

 the records was subsecjuently made on shore. The col- 

 lection of a large amount of wave data (and ultimately 

 synoptic oV)ser\'ations) recjuires that analyses be made 

 aboard ships and the spectral wave description be radioed 

 in a compact form. The development of suitable, simple, 

 compact and rugged analyzing equipment for routine 

 shipborne use is therefore needed. Application of the 

 rapidly developing transistor techniciues appears to be 

 indicated. 



27 Use of Wave-Measuring Buoys (Dorrestein, 1957; 

 Voznessensky and Firsoff, 1957) appears to be practical 

 on a sampling basis in a not- too-rough sea. With addi- 

 tional de\'elopment, .such buoys may be adapted to 

 measuring the directional-wave spectrum. Develop- 

 ments in this direction are recommended. They can 

 take the form of simple and cheap disposable devices, 

 or the more elaborate ones which will have to he set out 

 and sul)st'(|ueutly retrie\-e(l. 



28 Installation and Use of Wave-Measuring Devices 

 on Off-Shore Structures (Texas Towers) is recom- 

 mended. By extending the techniques developed by 

 Barber (Section 8.72), the determination of a large 

 number of directional wave spectra is feasible and should 

 he made. Again, it is recommended that the analyzing 

 equipment outlined in project 26) be used on the same 

 structure and that accumulation of a great mass of data 

 for later analysis be a\'oided. Howe^'er, the practice of 

 accumulating measurements for data analysis on shore 

 may be resorted to temporarily pending the availability 

 of the analyzing equipment. The nature of the record- 

 ing must be matched, however, to the analyzing equip- 

 ment to be used. Data are needed on a statistical basis 



