APS - Annapolis Performance Sailing


Sailboat Shackle Types & Uses

Sailboat shackles are the primary connection link in all manner of rigging systems.  They are used on line, blocks and rigging to make strong, lasting connections quickly and easily.  Stainless steel shackles are strong and corrosion resistant. They have a long service life, making them a top choice for most connections on a sailboat.

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Manufacturing Types

Manufacturing styles will vary between shackles and can dictate the shackles strength/load capabilities.

  • Formed sheet – Sheets of stainless steel are cut and pressed into the shape of a shackle over a form.  These are lightweight and the least expensive shackle, but the least strong.  These shackles universally use a clevis pin with a circular ring to secure them closed
  • Bar with coined ends – Round bars of stainless steel are pressed into the shape of a shackle using a form.  The ends are ‘coined’ with a hydraulic press to flatten them for drilling to accommodate the pin.  This creates high strength shackles at a moderate price point.  Pins will be formed from similar bar stock, threaded on one end, and ‘coined’ to a flat head on the other.
  • Cast – Molten stainless steel is poured into a mold which forms the body of the shackle.  This type of shackle is rarely used on a sailboat. This manufacturing technique is used to produce much larger industrial or architectural shackles.
  • Forged – Stainless steel is heated and pressed into a form under intense pressure.  This pressure realigns the grain of the metal to be more in line with the load it will support, thus making the shackle much stronger than a simple cast shackle. These are the strongest types of shackles.

Material Types

Stainless steel shackles are the most corrosive-resistant and are therefore ideal for marine applications.  Generally, they are made of type 316 stainless steel, which is considered “marine grade”. This steel contains molybdenum, which makes it the most resistant to corrosion in a marine or saltwater environment.

Pin Types

  • Clevis pin with a securing circular ring (ring-ding) allows you to reliably secure the shackle without the aid of tools.  Ring dings can snag on lines and cloth, so take this into consideration when choosing.  Once installed, the circular ring is often taped flat to the shackle to reduce snagging.
  • Slotted head threaded pins are fairly flush with the shackle body and tend not to catch on things like other pin types might.  They require the use of a flat screwdriver to install and uninstall.
  • Flat head threaded pins have a pronounced flat ‘ear’ on the end of the pin that allows for finger installation initially, and a final tightening with a pair of plyers or a rigging tool.
  • Drilled flat head threaded pins have the advantages of an undrilled version, but also allow you to more permanently secure the pin (mouse) with stainless seizing wire.
  • Key (lever) locking pins have a pin that is secured with a ¼ turn locking action.  The pin head is captive, and shaped/extended (single-winged or extended in one direction) out such that you can get a bit of leverage with your fingers to rotate and engage the locking action upon full close.

Captive vs. Non-Captive Pins

Threaded shackle pins are usually noncaptive, meaning that once it is unthreaded from the tapped lug of the shackle on the far leg, it can slide out and be completely removed from the shackle.  This can be helpful when installing in tight spaces, but can also lead to dropping and losing the pin overboard.  Captive pins are mated to the shackle such that you can unscrew the threaded pin from the tapped lug of the shackle, and slide it out to the point that the throat of the shackle is complete open and clear of the pin for fitting/attached, but the pin stays attached to the other shackle leg at the pin’s very end so you don’t lose it.

Shackle Types

Bow Shackles (Anchor Shackles)

The rounded design and larger loop shape of these shackles reduce their overall strength as compared to a D-shackle, but also allow them to take loads from multiple directions.  They are most commonly used on sailboat for connecting chain to an anchor where the chain/rode pulls from multiple angles on a dug-in anchor.  They are also the only shackle type recommended for bridle hoisting from multiple angles/attachment-points (imagine a bridle system to lift a dinghy on deck). 

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NOTE on Anchor Shackles: These are most often referred to interchangeably as a bow shackles, but a true anchor shackle will have a smaller “O” shape (smaller inside diameter in the rounded area), and are usually made of galvanized steel.  They will typically have the working load limit (WLL) stamped into the shackle.  For ground tackle requirements on a sailboat, either shape is typically fine – bow or anchor.

D-Shackles (Dee-Shackle)

These are a fairly narrow shackles shaped like a loop of chain (like the letter ‘D’).  Their shape is optimized for two directions of pull (straight line), which make them great for connecting pieces of gear together – blocks to padeyes or eye straps, eye spliced lines to blocks, blocks to traveler cars, etc.  D-Shackles are the most commonly found shackle on sailboat, and all other shackles are generally a variation on them.

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Long D-Shackle (Headboard Shackle)

These are a longer version of the D-shackle and are used for securing to objects with an attachment point that is located away from the outside edge or recessed.  They are also used to lengthen attachment assemblies, or raise attached gear or hardware.

Wide D-Shackles

These are similar to a standard D-shackle, and have a wider internal width.  They allow you to attach to objects that are irregular shaped or wider than normal.  Their load capacity is lower if the pin is point loaded towards its middle, as compared to a standard D-shackle.

Twist Shackle (90 degree shackle)

They allow two objects with 90 degrees difference in orientation to be joined, or to change the orientation of similar objects.  They are used most often when the objects are simple and do not articulate.  On sailboats they may be used to attach a simple loop block (or other gear) to a toe rail, pad eye or other attachment point that requires the block’s orientation to be permanently changed by 90 degrees.

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Halyard Shackles

They are most commonly used to attach a halyard to the head of a mainsail.  The shackle will have a retaining bar to keep the eye of a halyard captive so the shackle cannot slip off when the pin is open.  The shackle will generally have a key or lever type locking pin for easy finger (no tool) operation.

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Swivel Shackles

These shackles allow you to join two pieces of gear allowing them to freely rotate 360 degrees and also articulate on the pins.  The swivels may be either plain or low friction ball bearing.  They are used when it is desired that the angels of the attached gear change while loaded.  This could be a block attached to a fix point with a swivel shackle so that the block freely swivels, and the line can be adjusted from any angle.

2-Way Links

These allow you to attached two pieces of gear at 90 degrees of alignment to each other in the most compact space posible.  Attached gear is able to articulate on the pins in two different planes from each other.  This is a more compact solution to using a twist shackle.

Shackle Load

Load Direction – If you are using a shackle where the load on the shackle loop can vary from 0 to 90 degrees, you will need to use a bow shackle.  They are the only shackle designed to take multi angle loads.  For this reason, they are universally used for anchor connections.  The shackle is run through the last link of the chain which rests in the “O” part of the shackle, and the pin is secured through the fluke of the anchor.  The shackle cannot articulate side to side, so if the anchor is dug in and out of alignment with the load/direction of the chain, the chain can slide around inside of the “O” of the shackle by design, and not damage the shackle. D shackle and their variants are for straight line loading only, and should not be subjected to side loads like this.

Effects of Side Loading – Side angles of the load on a bow shackle will diminish the shackle’s strength.  Generally speaking at 0 degrees of side load (straight, inline load), the shackle will retain 100% of its load capacity.  At 45 degrees side load, you retain 70%, and at 90 degrees you retain only 50% of the shackles load capacity.

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