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 TB 55-1900-232-10
TABLE 5-3. Operating Range for Automatic Towing Machines on Various Types of Ships.
Types of Ships
Operating Range (lbs.)
Icebreaker (AGB)
35,000 - 80,000
Salvage Ship (ARS 6/38)
35,000 - 80,000
Submarine Rescue Ship (ASR)
24,000 - 60,000
Fleet Ocean Tug (ATF)
24,000 - 60,000
Towing and Salvage Ship (ATS)
15,000 - 96,000
Fleet Ocean Tug (T-ATF)
N/A
Salvage Ship (ARS 50)
25,000 - 115,000
NOTE
The tension (in lbs.) for the automatic operating mode can be set at any
point within the operating range shown.
manila and sisal (natural fiber) lines and wire ropes for hawsers. Since the early 1970s, nylon and other synthetic-fiber
lines also have been used for towing, both as hawsers and as pendants, with varying results. The following section
details the current engineering technology for design and selection of tow hawsers.
5-5.2.1 Required Strength. For a given tow assignment, towline tension forces and the appropriate factor of safety
are controlling elements in the initial selection of hawser size and tug Steady towline tension values may be calculated
according to the methods outlined in Paragraph 5-3. Calculate or approximate steady towline tensions for several wind
and wave conditions. The three main conditions are:
a.
Most favorable wind and sea conditions.
b.
Most probable winds and waves as forecast.
c.
Worst-case maximum winds and waves.
Obtain the appropriate safety factors from Table 5-4 and apply them for the tow system configuration to be used. Unless
it is known that dynamic loads will increase the steady state tensions by more than 100 percent, apply the safety factors
obtained from Table 5-4 to the steady state tension to determine the required hawser strength. The safety factor shown
in Table 5-4 should be increased appropriately if the tow is unfamiliar or there is significant uncertainty concerning the
degree of dynamic loads of the hawser.
Appendix N provides a means of estimating the extreme tension on a statistical basis. When these techniques are used,
use a safety factor of 1.5 against the "extreme tension". This does not supersede the Table 5-4 factors of safety. Both
must be checked since either may control for a specific set or circumstances.
5-24
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