TOWING MACHINES AND TRACTION WINCHES
The purpose of this appendix is to provide a brief overview of the functions and types of towing machinery
installed in U.S.
Navy tugs and towing ships. It is intended to assist in tow planning by providing an
understanding of the capabilities and limitations of the towing machinery in these ships. This appendix is not a
substitute for specific design or operating data contained in the technical manuals for the equipment installed in
an individual ship.
While some ocean towing is now performed by tug-barge combinations where the tug is mechanically attached
to the tow, this manual addresses the classic towing arrangement of the tug attached to the tow by a fiber or
wire hawser. The towing machinery must be considered the "main battery" of the tug and deserves
appropriate care in selection, design, operation and maintenance. An example of the importance of the
towing machinery is provided by the president of a major privately-owned European salvage and towing
company who reports that, for modern, high power tugs, the cost of the towing machinery at least equals the
cost of the ship's entire main propulsion plant.
K-1.1 NOMENCLATURE . Automatic towing machinery derives from the original "towing winch" Application
of steam power to the towing winch resulted in frequent use of the term "towing engine'." Today, "towing
machine" is the preferred term for automatic towing machinery and is the one used in the NAVSHIPS
TECHNICAL MANUAL. A non-automatic towing winch appropriately is called the "towing winch." The terms
traction "machines" or "winches" are both used, depending upon the number of automatic features installed.
K-1.2 FUNCTIONS OF TOWING MACHINERY.
All towing ships need a means of handling the towing hawser. Functions to be performed include:
a. Attaching the hawser to the tug
b. Adjusting the deployed length of the hawser
c. Stowing of the unused portion of the hawser
d. Providing for quick release while the hawser is under tension
e. Minimizing damage and wear to the hawser while in use and while stowed.
K-1.2.1 Attachment to the Tug . Older, smaller tugs may have no more than a bollard or bitts for attaching the
hawser. Smaller, European tugs often use a towing hook which swivels about a strong bearing on a platform.
More modern tugs generally combine the hawser securing function with the storage and/or transport
K-1.2.2 Adjusting the Deployed Length of the Hawser. Paying out additional hawser when secured to bitts
can be accomplished by hand, but at considerable personnel risk. When using a towing hook, which uses a
permanent eye at the end of a hawser, paying out hawser requires inserting a specific length of additional
hawser. In each case, shortening the length of deployed hawser is much more difficult and necessitates pwer
assistance if the hawser is under strain.
More modern ships incorporate the hawser adjustment function into
a powered winch or traction machine
K-1.2.3 Storage of Unused/Undeployed Hawser . On smaller, older tugs, hawsers may be simply faked down
on deck or stored on a reel which may be powered. Since the advent of wire hawsers, larger ocean tugs
generally combine the hawser securing, adjusting and storing functions into a self-contained winch.