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 TB 55-1900-232-10
centerline bullnose, chock or fairlead near the tow's centerline.
If the tow has a configurational, operational or directional stability problem that would make a single pendant inadequate,
a bridle should be rigged. Barges with square bows are rigged with bridles because of the stabilizing effect produced by
the bridle Some barges have a hull form and/or appendages which increase the directional stability of the barge. These
barges may be rigged with a pendant, rather than a bridle, attached on centerline. Chain is the preferred material for
bridles in deep ocean tow- ing and often complements or substitutes for the wire pendant. Chain's advantage over wire
derives from its greater weight per foot, which deepens the catenary, and from its superior resistance to chafing. As a
rule of thumb, the size of chain to use for bridles and pendants should be at least equal to the size of chain used to
anchor the tow An exception is for larger ships, where the 21/4-inch beach gear chain carried by Navy towing/salvage
ships is appropriately sized for the power and hawser size of the tow ship.
Because chain and wire bridles and pendants often are subjected to wear and abrasion during towing, it is recommended
practice to "over-design" to allow for wear, particularly for long tows. Tables in Appendices B and D provide the breaking
strength and weight per foot of various types of wire and chain. These tables can be used together with the calculated
towline tensions and factors of safety obtained from Table 5-4 to determine whether the available selected wire or chain is
sufficiently strong.
Emergency tows of merchant ships frequently use the tow's own anchor chain as a tow pendant. Appendix D also
includes data describing commercial chains A wire reaching pendant frequently is used with a chain pendant to simplify
connecting up the tow.
5-5.4
CONNECTION JEWELRY. The connect- ing components or towing jewelry utilized in rigging the tow system
include a variety of shackles, chain detachable links, special fittings such as flounder plates, end terminations for wire and
synthetic line, and splices in wire rope and synthetic line.
5-5.4.1 Safety Shackles. General purpose Navy shackles are described in detail in MIL-S-24214A (SHIPS) (Ref 14)
and in Appendix D. There are two types, two grades and three classes of shackles Of these twelve categories only four
are useable as tow- line connectors. These are as follows:
a. Type I Anchor Shackles
Grade A-Regular
Class 3-Safety Bolt and Nut
b. Type I Anchor Shackles
Grade B-High Strength
Class 3-Safety Bolt and Nut
c. Type II Chain Shackles
Grade A-Regular
Class 3-Safety Bolt and Nut
d. Type II Chain Shackles
Grade B-High Strength
Class 3-Safety Bolt and Nut
Navy shackles are permanently and legibly marked in raised or indented lettering on the shackle's body identifying the
manufacturer's name or trademark, shackle size and recommended Safe Working Load (SWL). Grade B shackles are
further marked with "HS," signifying high strength. SWL of both Grade A and Grade B Navy safety shackles is suitable
for sizing hardware for lifting purposes. However, SWL cannot be used as a substitute for, or m addition to, the
recommended factors of safety listed in Table 5-4 See also Appendix D for more detail on the application of factors of
safety to shackles.
5-28
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