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 TB 55-1900-232-10
More recently, two phenomena have led to development of traction machines that overcome problems inherent
in the typical winch:
a. The use of large, long, generally synthetic fiber hawsers The poor compression rigidity of the fiber
hawsers precludes transmitting the tensile load directly to a storage reel because the hauling part
would embed itself in the preceding layers of stored rope. Furthermore, this fiber's large bulk,
compared to that of comparable wire hawsers, requires a relatively large storage volume which is
impractical for reel-type storage. The unused fiber hawser generally is stored in a bin or dedicated
compartment, which may be adjacent to the traction machine. The traction mechanism operates on
the hawser and separates the hawser's unloaded, stored portion from its deployed, tensioned portion.
b. The second phenomenon, not yet seen in the U.S Navy, is the advent of very powerful tugs (on the
order of 10,000 horsepower and larger) which require very long, heavy, wire hawsers. These ships
often have two hawsers and towing machines. Each hawser may be 72 mm (2 7/8-inch) diameter and
as much as 1,800 M (5,900 feet) in length. Each such hawser weighs about 38 long tons and requires
a massive reel to store it, while also being robust enough to withstand direct application of tensile
loads carried by the hawser. Optimal location of the towing point is at the main deck, on centerline,
close to mid-length of the ship. This is prime space for arrangement purposes and presents a
significant drawback to stability when large weights are needlessly located at that height.
Consequently, these large tugs frequently use traction machines to transport and hold the wire, while
the unused wire is stored at more appropriate locations on relatively light storage reels. These reels
need only sufficient power to take up the slack between reel and traction machine. Wire hawser
traction machines are similar in principle and appearance to the fiber line machines familiar to the U.
S. Navy.
K-1.2.4 Quick Release of the Hawser under Tension. Emergency conditions, such as the tow's sinking or
being set toward danger, require quick release of the hawser, often while under strain Fiber hawsers may be cut
with an axe. Wire hawsers may be cut with an oxyacetylene torch or power cutters Each is hazardous and may
be impossible in a heavy seaway. The towing hook has an advantage in that it can be tripped, often remotely,
to release the hawser. For the typical reel-type towing winch, the reel can be disconnected from the driver
mechanism so that it will free-wheel, allowing the hawser simply to pull itself off the reel. The bitter-end
connection of the wire to the reel is easily defeated by the momentum of the wire coming off the reel. Traction
winches generally are able to be disconnected, and can be overhauled by the tensioned hawser. However, a
rapidly-running, large-diameter fiber hawser presents significant hazards to personnel and equipment. Unless
the bitter end of the hawser is very close to the traction mechanism, the unloaded portion of the hawser may
have to be cut.
K-1.2.5 Protection of the Hawser. There are two principal concerns The first is minimizing damage and wear
to the hawser because of scuffing, abrasion, small-diameter bending, crushing of stored layers under loaded
turns on a reel and protection from adverse environmental conditions. The second principal concern is
protection of the hawser from overload due to surges caused by relative movements of tug and tow in a
seaway. The former considerations are addressed by careful design of arrangement of towing machines and
deck equipment. The latter concern (overload) is met in part by proper operating parameters (speed, scope of
hawser and course) and often by inclusion of automatic payout and retrieval features in towing machinery. Both
concerns are further eased by use of towing machinery instrumentation that provides hawser tension and scope
readouts. This instrumentation may operate independently of towing machinery. The next section expands on
the reasons for including automatic features on towing machinery.
K-2
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