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 TB 55-1900-232-10
automatic towing machines and load-sensing systems. An automatic towing machine's feedback and load
response provide the capability of reducing dynamic loads and, if necessary, rapidly releasing the towline.
Table 2-2 lists the various classes of towing ships operated by the U.S. Navy. These ships are capable of
long-range tows and other missions. The T-ATF is a multipurpose, long-range, high-horsepower, sea- worthy
tug. It can conduct long-distance tows, and when augmented with additional crew and equipment, operate in
support of firefighting, diving and salvage missions. The ARS 50 is a salvage tug with a double-drum towing
machine. It carries a crew and equipment sufficient to handle independent salvage, diving, damage control
and firefighting capabilities in time of war
The ARS 38 (Rescue and Salvage) and ATS (Towing Salvage) Classes have similar capabilities and sufficient
personnel to perform ocean towing.
Although they have somewhat lower propulsion power than other classes, the ASR (Submarine Rescue) Class
ships, with the exception of the ASR 21 and ASR 22, are equipped with towing machines. They are capable of
rescue as well as routine towing. See Figures 2-1 through 2-6 for information regarding major specifications
and visual appearance of the various Navy ocean tugs.
2-3.2
TUG DESIGN CONSIDERATIONS. The specific items to be considered in the design of an ocean
tug are dependent upon the missions and services that it will be called upon to perform In general, a Navy
ocean tug is a very versatile ship, but its design involves many compromises. The services that the tug may be
required to furnish to its tow can cover a very wide spectrum of needs. For long ocean tows, the tug can be
called upon to provide complete logistic support for the tow and the riding crew, if it is manned During rescue
salvage towing operations the tug may also be required to serve as a supply base and shop for repairs, rigging
and damage control. Trade-offs and compromises must be made in terms of mission and operational factors by
choosing among the many sub-items listed. Appendix J provides data on features and compromises in an
ocean tug.
2-3.3
TUG POWERING AND BOLLARD PULL. The design of the main propulsion power plant must be a
compromise among the needs for high free- running speeds for reaching the scene of a casualty, good
economy with high towline pull for long- distance tows at reasonable towing speeds and high bollard pull. The
latter is necessary for such activities as holding a distressed ship to prevent it from grounding, and for refloating
stranded ships. In the absence of a good automatic towing machine or other accurate means of measuring the
towline tension, as knowledge of the tug's available towline pull and bollard pull is required for controlling the
tension Chapter 5 presents the methodology for estimating towline pull and bollard pull
2-3.4
FENDERS. Fenders are energy-absorbing materials or devices that protect both the tug and the tow
Standard fenders currently in use generally are either molded rubber or specially-designed, foam- filled and
pneumatic-type devices. These are discussed in the following paragraphs and illustrated m Figures 2-7 and 2-
8.
2-3.4.1
Subsurface Fenders. Tugs working along-side submarines should have subsurface fenders
2-3.4.2 Modern Pneumatic And Foam Fenders. Modern fendering is an important part of towing operations
when alongside evolutions are required, either in harbors or at sea Three types of fenders are available They
are high-pressure (5 to 7 psi) pneumatic, low-pressure (1 psi) pneumatic and closed-cell foam covered with
urethane elastomer In the following list, the first six features are most significant Important characteristics
include.
(Text continued on page 2-15)
2-5
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