Friday, February 20, 2015

Swivel Anchor Connectors

Swivel Anchor Connectors. Anchor connector testing : Manufacture of chain in all materials and sizes is a closely controlled operation, using well-understood methods.

The product is inspected and tested before dispatch to the point of sale, resulting in a reliable product that rarely gives problems in service.  Likewise, the better modern anchors are engineered to exacting standards and tested to ensure that these are met.  But what of the shackles, links and swivels that connect the two together?  Any yachtsman browsing the pages of the ybw.com forums or the magazines will find no shortage of questions and discussion about the merits of the various types available, and quite a number of horror stories detailing failure of some of them. Manufacturers have reacted to these well-documented problems by producing new designs that appear to be well engineered.  However, the only way to determine the strength of these fittings in practice is to test them to destruction.

We designed a programme to assess the strength of a wide selection of such fittings, using a standard tensile testing machine. Chain, shackles, swivelling and fixed connectors and various links were purchased in well-known chandleries in the UK. The intention was to use 8 mm as the standard size, increasing this in accordance with recommendations that one size larger may be required in some cases. A few larger sizes were tested for interest.

It is rarely possible to find the materials of construction of fittings on sale in chandleries.  Better quality fittings may have their materials stamped on them, for example 316 stainless steel.  It is usually possible to tell a galvanised fitting from a stainless steel one but otherwise assumptions must be made.  Galvanised chain is normally a hot forged low carbon steel, producing a tough material of adequate strength.  Fittings such as shackles are made by a variety of methods that are cost dependent, cast or stamped being the cheapest and drop forged the most expensive. As might be expected, the most expensive are the strongest, so in general you get what you pay for.  A good guide can be that better equipment will have a safe working load (SWL) value stamped into its surface.  Galvanised shackles intended as components of lifting and hoisting equipment tend to be stronger than the standard chandlery item and are little more expensive. The SWL figure of lifting equipment allows a factor of safety of at least six, whereas that for chain is normally four.