Because of the great difference in strength between Grade A and Grade B shackles, pay
particular attention to the presence or absence of the HS mark, indicating a high strength
shackle. The user must be sure that proper shackles are used in the system.
Grade B, High Strength shackle pins and bolts are marked by the raised letter "HS" on the head. Grade A shackle
pins are not specifically marked.
Screw-pin shackles, other than the special forged shackles for stoppers, must never be
used for connections in towing rigs. The pin could back out due to the constant vibration
set up by the hydrodynamic actions on the towline. Although screw-pin shackles are a
commonly used type of marine shackle and afford a quick and simple means of
connecting and disconnecting, the screw- pin shackle should not be used for connections
in a towing rig
Cotter keys are not used in towing, despite MIL-S- 24214A (SHIPS) drawings.
Never weld on forged steel shackles. The welding process can weaken the shackle.
Navy shackles are made of forged steel; welding to forged steel shackles can reduce the strength of the shackle by as
much as 30 percent Shackles should never be welded on; neither should pins be secured by welding The nuts on safety
shackle pins are secured by a small bolt, with two jam nuts to secure the pin nut. Cotter keys are not used in towing,
despite MIL-S-24214A (SHIPS) drawings.
5-5.4.2 Other Connecting Links . In addition to safety shackles, there are several other connecting devices used in
rigging chain and wire pendants, bridles, etc. These include
Detachable links (Navy and Kenter-type)
Detachable anchor connecting links (Pear- shaped or detachable end link)
The plate shackles shown in Appendix I are commonly used to make connections to the flounder plate and to
connect chain and wire pendants.
Never weld detachable links. The welding process can weaken the links.
When inspecting chain, inspect the detachable links to determine whether they have
been properly assembled. The key slot must be in the proper place and the match
marks must be identical and matched. This is necessary because detachable links are
hand-fitted to ensure proper assembly and full strength. All assembled links should be
visually inspected and sounded.
The practice of welding detachable links closed to assure security of the towing rig is one that continually plagues towing
commands Welding detachable links should never be allowed It is much safer and more cost-effective to use a hairpin to
secure the tapered pin in the link This ensures that it will not come apart, while simplifying eventual disassembly and re-
use of the link. Details for modifying detachable links for use with hairpins are contained in Appendix D. Detachable links
should not be used in instances where they might be subjected to bending or twisting.
5-5.4.3 Wire Rope Termination.
Three types of wire rope terminations normally are