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TB 55-1900-232-10
Chain is an important component in the connection between the towed vessel and the tug. It usually appears m
the form of pendants or bridles at the towed-vessel end of the towline The chain components serve one or
more of the following purposes:
a. A chafing-resistant strong terminal connection to the towed vessel
b. An equalizing device (bridle) to share the towing load between two strong points located port and
starboard of the towed vessel's bow (or stern)
A means of absorbing dynamic loads in the tow- line, by virtue of its weight, which increases catenary in
the towline.
The traditional Navy die lock chain, with the stud integrally forged into the link, is no longer manufactured.
Nonetheless, large amounts of die lock chain remain throughout the Fleet and this type chain is perfectly
acceptable for all uses for which it was designed. The Navy now purchases "flash butt welded stud link" chain
that is similar in appearance to high quality, commercial anchor chain, usually referred to as "welded" or "stud
link" chain. In this appendix, this new Navy chain will be called "stud link" chain for the sake of simplicity. Navy
stud link chain is slightly stronger than standard Type 1 die lock chain, they may be used interchangeably.
Until recently, commercial "DiLok " chain was made by one manufacturer, Baldt, and is slightly stronger and
heavier than Type 1 standard Navy die lock chain. Section D-11 discusses the strength of the various chains
that may be used in towing.
D-2.1 TRACEABILITY. 'Traceability, or the ability to trace a chain and what has happened to it back to its
source, is an important element in accident investigation as well as in general product- improvement efforts For
identification, a corrosion- resistant metal tag is attached to the end link at each end of each shot or length of
Navy chain. Included among data plainly marked on the tag is a manufacturer's serial number that permits
tracing the chain back to its manufacturing source. The manufacturers also provide information with new chain
that covers size, type, material, proof tests, certification, etc. This information should be maintained in the
Towing Hawser Log, see Appendix F, and updated as necessary for chain that is used as an integral part of the
towline connection.
D-2.2 MARKING. Navy chain, whether die lock or stud link, is marked in accordance with MIL-C- 24633 (Ref.
Commercial chain used in marine service, including "DiLok,' is controlled and certified by the various marine
classification societies such as the American Bureau of Shipping (ABS), which certifies all US. Flag vessels
and many foreign ships. Marine stud link chain is made in three grades, as shown in Table D-2. Grade 2 is most
prevalent. ABS requires chain to be marked on the end link of each shot, or every 15 fathoms, if the chain is
continuous-i.e., without connecting links. The markings include:
a. Certificate number
b. Chain size
Classification society stamp (a Maltese Cross for ABS)
d. Designation of the type of chain, e g., AB/1, AB/2 or AB/3


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