shackle

A shackle is a U-shaped piece of metal secured with a pin or bolt across the opening, or a hinged metal loop secured with a quick-release locking pin mechanism. They are used as a connecting link in all manner of rigging systems, from boats and ships to industrial crane rigging. As an automotive term, it refers to a link connecting the leaf spring to the frame.

A carabiner is a variety of shackle used in mountaineering.

Types

Pin shackle

A pin shackle is closed with a clevis pin. Primarily used above the deck, pin shackles used to be the most common shackle used aboard boats. Pin shackles can be inconvenient to work with at times because they are secured using something else, usually a cotter pin or seizing wire.

Threaded shackle

The pin is threaded and one leg of the shackle is tapped. The pin may be "captive", to prevent it from dropping loose. The threads may gall if over-tightened or have been corroding in the salt air, so a liberal coating of lanolin or a heavy grease is not out of place on any and all threads. A shackle key or metal marlinspike are useful tools for loosening a tight nut.

Mousing

For safety, it is common to mouse a threaded shackle that is going to be left done up for some time in anything like a critical application. This is done by passing a couple of turns of mousing wire through the hole provided for this purpose in the unthreaded end of the pin and around the body of the shackle's hoop.

Alternatively, some threaded shackles are provided with a hole through the threaded end of the pin beyond where it emerges from the threaded hole. A cotter pin or a couple of loops of mousing wire through this hole serves the same purpose and secures the shackle in a closed position. Nylon Zip-Ties are also commonly used in applications such as theater where the shackle must be secured, but easy removal of the mousing is required.

In this context, 'mouse' and 'mousing' are often pronounced with a harder 's', like mouze and mouzing.

Galvanic corrosion

See main article Galvanic corrosion

Note that when mousing, the introduction of any other metal into permanent, direct contact with a safety-critical shackle may seriously reduce its (or the other metal's) useful life, especially under water and more especially under sea water. Frequent wetting or immersion, followed by exposure to the air again, is absolutely the worst combination. This is particularly relevant to shackles that form part of permanent moorings and anchor cables. For this reason, specially alloyed mousing wire is available and should be exclusively used for this purpose at all times. The use of galvanised or stainless steel cotter pins can have similar drawbacks.

Snap shackle

A snap shackle spliced to a line.

As the name implies, a snap shackle is a fast action fastener which can be implemented single handed. It uses a spring activated locking mechanism to close a hinged shackle, and can be unfastened under load. This is a potential safety hazard, but can also be extremely useful at times. The snap shackle is not as secure as any other form of shackle, but can come in handy for temporary uses or in situations which must be moved or replaced often, such as a sailor's harness tether or to attach spinnaker sheets. Note: When this type of shackle is used to release a significant load, it will work rather poorly (hard to release) and is likely to have the pin assembly or the split ring fail.

D-shackle

Also known as a chain shackle, D-shackles are narrow shackles shaped like a loop of chain, usually with a pin or threaded pin closure. D-shackles are very common and most other shackle types are a variation of the D-shackle. The small loop can take high loads primarily in line. Side and racking loads may twist or bend a D-shackle.

Headboard shackle

This longer version of a D-shackle is used to attach halyards to sails, especially sails fitted with a headboard such as on Bermuda rigged boats. Headboard shackles are often stamped from flat strap stainless steel, and feature an additional pin between the top of the loop and the bottom so the headboard does not chafe the spliced eye of the halyard.

Twist shackle

A twist shackle is usually somewhat longer than the average, and features a 90° twist so the top of the loop is perpendicular to the pin. One of the uses for this shackle include attaching the jib halyard block to the mast, or the jib halyard to the sail, to reduce twist on the luff and allow the sail to set better.

Bow shackle

With a larger "O" shape to the loop, this shackle can take loads from many directions without developing as much side load. However, the larger shape to the loop does reduce its overall strength. Also referred to as an anchor shackle.

References

• Edwards, Fred (1988). Sailing as a Second Language. Camden, ME: International Marine Publishing. ISBN 0-87742-965-0.
• Hiscock, Eric C. (1965). Cruising Under Sail. Oxford University Press. ISBN 0-19-217599-8.
• Marino, Emiliano (1994). The Sailmaker's Apprentice: A guide for the self-reliant sailor. Camden, ME: International Marine Publishing. ISBN 0-07-157980-X.

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