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 TB 55-1900-232-10
not occur frequently in the tables, but does happen sometimes when shifting between different families of
curves on Figures L-2 through L-5. This is caused by the curve-fitting program, which attempts to provide the
best fit at about 70 percent of hawser strength, accepting some error at lower tensions.
The hawser tension trends for the previous examples do not experience the abnormality demonstrated here. It
may be assumed that the extreme tension probability with 1,800-foot scope of wire will be better than, or
certainly no worse than, at 1,200-foot scope.
L-5.5 ARS 6/38 CLASS. The ARS 6 and 38 Classes have the same hawser as the ATF 76. Limits of mean and
extreme tension are 96,000 and 192,000 pounds, respectively.
The Appendix G example predicts a tow speed of 4.4 knots at 47,000 pounds hawser tension. Mean tension is
satisfactory in this case. Because of the lower speed, enter Table L-13 at the 25-knot wind/3-knot tow speed
section.
Wave
Wire
Extreme
Direction
Scope
Curve No.
Tension
0
1,000
6
131,000 lbs.
0
1,200
4
103,000 lbs.
0
1,500
31
117,000 lbs.
0
1,800
30
105,000 lbs.
These predicted extremal tensions are well under the allowable dynamic tension of 192,000 pounds, and the
tow may be performed with acceptable risk. Towing speed is limited by the available power of the towing ship.
As in the previous case, note that there is an apparent increase in predicted extreme tension as the table shifts
from one family of curves (straight lines in figure L-2) to another family. These differences should not be taken
literally; it can be assumed that longer scope will reduce the risk of extremal tensions resulting from ship
motions.
L-10
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