Appendix IV – Hardware Ratings, Chain and Rope Strengths

A Basic Sampling. Refer to Manufacturer's Data Sheets for Actual Figures

SWL & BL Rating Methods

Most hardware, chain and rope manufacturers provide two different ratings: 1) SWL (safe working load) and 2) BL (ultimate breaking load). Safe working loads are given as guides only and most manufacturers warn that the SWL should not be exceeded. Ultimate breaking loads are usually at least four times the safe working load and sometimes as high as six times. Some manufacturers provide an intermediate rating known as the PL (proof load). The proof load (usually twice the SWL) is the load which the product withstood without deformation when new and under laboratory test conditions.

 

Screw Pin Anchor Shackles

These are usually the sort of shackles one ends up using for anchoring purposes. The SWL ratings are usually stamped on galvanized ones. Stainless steel screw pin anchor shackles have similar ratings. The following apply to galvanized ones made in Japan, for example:

SIZE SWL BL
1/4" 1,000 lb. 6,000 lb.
5/16" 1,500 lb. 9,000 lb.
3/8" 2,000 lb. 12,000 lb.
7/16" 3,000 lb. 18,000 lb.
1/2" 4,000 lb. 24,000 lb.
5/8" 6,500 lb. 39,000 lb.
3/4" 9,500 lb. 57,000 lb.

 

Swivels

Stainless steel swivels are preferable to galvanized ones, though strength ratings may be similar. The following apply to good quality galvanized ones made in Japan:

SIZE SWL BL
1/4" 850 lb. 4,250 lb.
5/16" 1,250 lb. 6,250 lb.
3/8" 2,250 lb. 11,250 lb.
1/2" 3,600 lb. 18,000 lb.
5/8" 5,200 lb. 26,000 lb.
3/4" 7,200 lb. 36,000 lb.

 

Chain Ratings

Three different types of galvanized chain can be incorporated into the anchor, sea anchor or drogue tether. 1) Proof Coil. 2) BBB. 3) High Test. The longer links found on proof coil are not compatible with most windlasses. BBB's shorter links are. High Test chain has the highest strength-to-weight ratio but the odd size link requires a windlass that will accept it.

 

Proof Coil & BBB

SIZE SWL BL
1/4" 1,250 lb. 3,000 lb.
5/16" 1,900 lb. 5,000 lb.
3/8" 2,600 lb. 10,600 lb.
1/2" 5,500 lb. 18,000 lb.
5/8" 6,900 lb. 27,600 lb.
3/4" 9,750 lb. 39,000 lb.

 

High Test

SIZE SWL BL
1/4" 2,600 lb. 7,750 lb.
5/16" 3,900 lb. 11,600 lb.
3/8" 5,400 lb. 16,200 lb.

 

Basic Nylon Rope Strengths

High quality treated ropes may be significantly stronger and up to 5 times more abrasion resistant than the cheaper, commercial-grade economy brands sold at ordinary hardware stores. As far as drag device tethers are concerned, braid may be preferable to three strand as it does not torque (try to unlay) under load. Most three strands will provide about 16% stretch at 15% of their breaking strengths, while most braids will provide about 7-10% stretch thereabouts.

 

Premium Three Strand

SIZE Average Break Strength
1/4" 2,000 lb.
3/8" 4,400 lb.
1/2" 7,500 lb.
5/8" 12,200 lb.
3/4" 16,700 lb.

 

Single Braid (European "Multiplait" Equivalent)

SIZE Average Break Strength
1/4" 2,000 lb.
3/8" 4,400 lb.
1/2" 7,500 lb.
5/8" 12,200 lb.
3/4" 16,700 lb.

 

Premium Double Braid

SIZE Average Break Strength
1/4" 2,300 lb.
3/8" 4,900 lb.
1/2" 8,500 lb.
5/8" 15,300 lb.
3/4" 19,700 lb.

 

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Using Parachutes, Sea Anchors and Drogues to Cope with Heavy Weather – Over 130 Documented Case Histories