Science Fair Project Encyclopedia
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 is known as a shackle. They are very commonly used in outdoor activities such as sailing.
The primary types include pin shackles, threaded shackles, and snap shackles.
- 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. Because pin shackles are secured using something else, usually a cotter pin or seizing wire, they are definitely more complex to work with while hanging in a bosun's chair on a halyard 20-40 feet above the deck wishing you had a third hand.
- Threaded shackle
- The pin is threaded and one leg of the shackle is tapped. The pin may be 'captive', and not able to be dropped into the drink. (There are few sounds more depressing than the ping - plonk as the pin hits the deck and bounces overboard while you're hanging from the masthead...) A threaded pin may also have a hole into which a cotter pin can be inserted. The threads may gall if over-tightened or have been corroding in the salt air, so a liberal coating of lanolin is not out of place on any and all threads, and a shackle key or metal marlin spike are useful tools for loosing a tight nut. Unlike the pin shackle, a threaded shackle can stay together just with threads. For safety, however, it is usually wired or cotter pinned to secure in a closed position.
- 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 (a potential safety hazard, but also 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.
Shaped and Specialty Shackles
- A narrow shackle shaped like a loop of chain, usually a pin or threaded pin closure. This is probably the most common shackle type, and most others are a variation on the theme. The small loop can take high loads primarily in line. Side and racking loads may twist or bend this shackle.
- This longer version of a D shackle is used to attach halyards to sails, especially sails fitted with a headboard such as on Marconi 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.
- 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.
- 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 over-all strength.
- Edwards, Fred; Sailing as a Second Language; International Marine Publishing Company; © 1988 Highmark Publishing Ltd.; ISBN 0-87742-965-0
- Hiscock, Eric C.; Cruising Under Sail; Oxford University Press; Second Edition © 1965 Oxford University Press; ISBN 0-19-2175222-X
- Marino, Emiliano; The Sailmaker's Apprentice: A guide for the self-reliant sailor; International Marine; © 1994 International Marine/Ragged Mountan Press; ISBN 0-07-157980-X
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