practical survey speed and could substantially reduce overall survey time. 

 The types of vessels used for coring operations are usually slow, and unless 

 the vessel to be used is already known, a speed of about 5 knots is reasonable 

 for estimating time schedules. 



131. Downtime due to weather is often a significant factor in explora- 

 tion costs. With surface -towed acoustic sources and receivers, the quality of 

 seismic reflection records progressively deteriorates when waves exceed 1 m in 

 height. Similarly, the efficiency and safety of coring operations deterio- 

 rates as wave heights increase. While some improvement in seismic reflection 

 data can be achieved by using submerged source and receiver combinations that 

 are less affected by wave motions, much time may also be lost when wave 

 heights become hazardous to the vessel, and all operations must be suspended. 

 It is, therefore, advantageous to schedule field operations to coincide with 

 the season of most favorable weather and/or sea conditions. This can be 

 determined best by analysis of historical sea and swell data for the explora- 

 tion area. 



132. Downtime can also occur because of malfunction of essential equip- 

 ment. This can be avoided or minimized by having a trained technician in the 

 field party who can maintain and repair equipment, and by having backup equip- 

 ment either on hand or available on short notice from the manufacturer or 

 equipment rental source. 



Equipment 



133. A list of equipment needed for the exploration program should be 

 compiled during the planning stage for the purpose of cost analysis and pro- 

 curement of necessary items. A sample equipment list, modified from Prins 

 (1980), is contained in Appendix A. The most costly and important items are 

 the vessels used for support of the geophysical and coring operations. It is 

 essential that vessels contain enough space to accommodate the equipment, and 

 are capable of operating under the expected predominant sea and swell condi- 

 tions. Although some vessels are designed for marine research activities and 

 have special features to facilitate use of the types of equipment required for 

 an exploration program, installation of these items in an otherwise suitable 

 vessel can usually be accomplished in one or two days. 



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