1164 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1957 



fathometer records of the Mid-Atlantic Ridge provided by Professor 

 Bruce C. Heezen of the Lamont Geological Observatory. Laying down 

 this slope at a ship speed of six knots requires a slack of 8.5 per cent (see 

 Section 5.1). If the slack were only 5 per cent, the successive cable con- 

 figurations as calculated by the methods of Appendix E would be those 

 shown in Fig. 22(a).* The cable would touch bottom after 2.6 minutes, 



t IN minutes: 







(a) DESCENT 



2710 LBS 



-990' *\ 



1320' 



(b) ASCENT 



Fig. 22 — Successive cable configurations during a 35-fatiiom descent and as- 

 cent lay of cable No. 2 at a 6,000-ft depth with an assumed 5 per cent slack and 

 6-knot ship speed. 



leaving a residual suspension with a half-span of 480 feet and a tension 

 of 525 lbs. The mean tension at the ship would correspondingly increase i 

 by 525 lbs during the 2.6 minute time interval. In even moderately^ 

 rough seas, this tension change could be obscured by the ship motioni 

 tensions. 



Consider this profile next to represent an ascending lay under a shipi 

 speed of six knots. Fig. 22(b) shows the initial {t = 0) and residual cable* 

 configuration. Because of the small incidence angle of the initial straight- 

 line shape, the residual half -span of the catenary is a quarter of a mile 

 (1820 feet) long, and the accompanying residual tension is 2,710 lbs, or 

 roughly that which normally occurs in laying at a depth of f of a nautical 

 mile. At the ship, there would be a decrease in the mean tension of 130^ 

 lbs. corresponding to the 35 fathom decrease in depth. Again, a tension 

 change of this magnitude would be difficult to discern because of ship 

 motion tensions. 



* We have further taken the ratio wh /EA to be 3.1 X 10"^ in this computation. 

 However, the results are very insensitive to change in the wh /EA ratio. 



