Shackles
Shackles are the standard method of attaching the anchor to its rode, the section of which closest the anchor is typically chain. They offer better value-for-money than their alternative swivel connectors. They also tend to be the weakest link in terms of physical strength of the entire anchor tackle, so maximizing their quality and reliability is of great importance. Good quality high end shackles are not costly so there is no excuse to compromise on this element of the system.
Contents
Materials
We recommend the use of tested shackles, especially on anchor sizes of above the Rocna 15 (33 lb). As with chain, galvanized models represent the best economy. Stainless steel shackles are popular but care with regard to quality should be taken.
A forged type is preferable, and cast versions should always be tested. To minimize the 'weakest link' factor, a 'high load' or 'heavy duty' level of strength is preferable. High tensile grades of steel of 600 MPa or higher (G6 / G8) are available.
Some high quality shackles designed for high load have colored pins as a form of branding. This is just paint on top of the galvanizing. It will wear off with use, but this is no issue.
A great deal of low quality product comes out of Asia, and extra care should be taken. However, some Chinese shackles are reputable and reliably rated.
Types
Shackles are available in numerous different configurations for a wide variety of purposes.
The body
The standard configurations are the straight D (or U) shape, and the bow shackle. The latter is recommended for a single shackle being used with an anchor, as the shape of the bow can better handle articulating pulls from the rode, although this is not critical. Working load limits are typically even between the two shapes.
The pin
A regular pin (screw collar pin) can be tightened and undone by hand, although pliers may be necessary after some time left tightened. Seizing however is required. Safety bolt designs require spanners (wrenches) to both tighten and undo, but require no seizing, and are recommended unless the anchor and rode are to be regularly parted. Other variations for specialist purposes exist.
Sizing and installation
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The topic of this section refers to an aspect of the Rocna anchor which the Rocna User's Guide deals with.
To view the User's Guide in multiple languages, click here: Rocna User's Guides |
The shackle should be selected according to the largest size the pin of which will fit through the end link of the chain. Some anchor chain has an over-sized link (or links) at the end, which allows the shackle to be larger and stronger.
Some anchors will not accept the head of an adequately sized shackle, being designed for the pin instead. This necessitates the use of two shackles, connected body-to-body with each other, and the pins through the anchor and the chain respectively. This is less than elegant, and doubles the chance of a shackle failure – well designed anchors, including the Rocna, have an elongated rode attachment point through which the shackle head can pass.
Matching the shackle to the chain
The rode attachment points on the Rocna range are designed to accept the head and body of any shackle matching any chain which could reasonably be expected to be used. Low grade shackles can have pins and bodies of the same diameter, but higher grade and "high load" shackles tend to have bodies smaller than their pins.
Below is listed common chain sizes, and the shackles (as defined by their pin diameter) which will fit. Chain can have a larger end link, intended to permit the use of a larger shackle. With high load shackles, this is generally not necessary.
This data is intended as a guide only and actual measurements may vary.
| Chain | Shackle pin size | Typical high load body diameter | Rocna rode attachment point compatibility |
|---|---|---|---|
| 6 mm | < 8 mm | < 7 mm | |
| 7 mm | < 9 mm | < 8 mm | |
| 8 mm | < 10 mm | < 9 mm | |
| 9 mm | < 12 mm | < 11 mm | |
| 10 mm | < 15 mm | < 13 mm | |
| 11 mm | < 15 mm | < 13 mm | |
| 12 mm | < 16 mm | < 13.5 mm | |
| 14 mm | < 18 mm | < 16 mm | |
| 16 mm | < 22 mm | < 19 mm |
Seizing
A regular screw collar pin shackle must be seized with two turns of soft stainless steel or monel seizing wire. The wire must be wrapped and twisted such that it cannot undo. An alternative short term solution is to use a suitably sized electrical cable tie. This prevents the pin from undoing itself, which it is certain to do otherwise.
Alternative configurations such as countersunk screw pins and safety bolt designs do not require this, but are not as readily available in suitable sizes or materials apt for marine applications.