Reliable running riggingJan 1, 2003
Years ago, blasting across the Southern Ocean during the Whitbread Round the World Race, we thought everything was going along smoothly. Flying the number 4 jib, we were powered up, and the cold, dense air provided plenty of load on the equipment. We had been checking the sheet leads several times each watch to ensure that the lines' covers weren't being worn through, rolling halyards to change the loading points, and remaining alert. We had run two jib sheets for the port side, one as a safety back-up line. Most of the load was taken on the Kevlar line and some was taken on the pre-stretched Dacron. However, even with all our preparation and diligence, things were about to get ugly.
For starters, the bowline blew out on the Kevlar sheet. Much of the line's strength had been lost in the sharp turn of the knot. Perhaps more of the load should have been taken up on the more stretchy Dacron line. Later that same night, the Dacron sheet chafed through the cover as it passed the cap shrouds. While these were two quickly resolved problems, they started an interesting debate on how best to handle lines and understand their unique properties. Which lines work best for racing or for voyaging applications? How should they be selected, sized, and attached? What helps them to keep on working throughout the season, and what causes premature failure? There's more to these questions than just chafe.
It may seem self-evident, but the first task is to select the right line for the job. Tom Yale of Yale Cordage suggests that there's relatively little point for voyagers to use more expensive high-modulus line as sheets on Dacron sails. Considering the actual length of the line under load and how little that would actually stretch, and the fact that there is some stretch in the Dacron sail cloth, the line would be mismatched to the task. The strength of a particular line is certainly of critical importance. On an efficiently sailed boat, weight and location of that weight are also high-priority considerations. The more mass there is for a given wind strength to accelerate, the slower the acceleration will be. If the owner of a boat is working to a fixed budget for his running rigging, the best place to invest the extra money in high-tensile, relatively lightweight line is up the rig in the halyards. Weight is reduced; inertial righting moment and reliability are increased. But the weight of the line is only part of the total weight. Water retention in the line's fiber, whether from a rain squall or from high humidity, is also part of the overall equation.
Synthetic line properties
With all of the various types of synthetic lines available, it's becoming increasingly important to understand the various properties possessed by each. Creep, UV resistance, susceptibility to abrasion, and moisture retention are a few of the properties that vary as well as the breaking strength for a given diameter of line. Vectran (or Vetrus) and Technora are a couple of the newer synthetic lines that have appeared since Kevlar and Spectra first came on the market.
Hydrophobic (fibers that resist moisture retention) fibers include Spectra, Vectran, and olefins. Hydroscopic (fibers that tend to readily absorb moisture) fibers include polyester, Kevlar, and Technora. If you're trying to select line for halyards, you will want to keep the total weightincluding moistureas low as possible for a given amount of strength. For racers that might mean Vectran or a high grade of Spectra for the jib halyards, or Spectra for the spinnaker halyard. Vectran has a particularly low moisture-absorption rate. When used in halyards, some hydroscopic synthetics may show a weight gain of 8% in high-humidity conditions (even on a nice sunny day with 60% relative humidity), and they may even double their weight when subjected to rainfall. For voyagers, a Spectra-cored blend or a high grade of low-stretch polyester would probably be a good choice.
Creep, the elongation of the fibers that occurs over time, had been one of the persistent problems with earlier synthetic lines. With some grades of Spectra, creep to rupture could occur at 95% of a line's designed maximum load. The application for which a line is intended to be used can be critically important to achieving a desired result.
Yale suggested that there are three components to fiber elongation. Elastic elongation occurs when a line that is loaded with several hundred pounds will stretch a given amount and immediately spring back part of the amount that has been stretched when the load is removed. Hysteresis is a type of elongation that will give back a little more of the stretched amount over a period of time. In permanent elongation a line will, to a certain extent, be permanently stretched. Yale suggests that the best way to break in a new line and make it more stable is to secure one end to a very stable hard point on the boat and winch the line tight. Have it stay there over a period of time to remove the permanent component of elongation in traditional polyester ropes.
Stretchiness in some lines may not only be tolerable, it may even be desirable. Lazy jacks can be made from Dacron if weight aloft isn't too much of a consideration. And dock lines, of course, should have some stretch to absorb the constant cycling of loads while absorbing much of the shock rather than transferring it all to the deck hardware. On extended voyages, it may be desirable to have sheets made out of pre-stretched Dacron, which will allow for some stretch in the line. A safety sheet can also be run and tensioned with less load, limiting the play in the primary sheet and providing for a back-up in case the first sheet fails under load.
Selecting the right line
Selecting the right type of line for the job is the first task. Cost is almost always a consideration even when performance is a high priority. All of the synthetic fibers have their own unique sets of properties such as chafe resistance, ratios of tensile strength to weight, the degree to which they will creep or elongate under load, whether they tend to be hydrophobic or hydroscopic. Some lines are blends of higher-modulus, high-tensile strength fibers such as Spectra or Vectran combined with other fibers such as a polyester. And there are a number of polyester fibers; Dacron is only one particular type of polyester produced by DuPont. Even Spectra has a few different types, including 900 and 1000. Spectra 1000, while costing somewhat more, also has approximately 20% more strength for the same diameter of Spectra 900, and Spectra 1000 also has lower stretch.
To ensure continued reliability and control operating costs, the line needs to be properly cared for. Chafe is probably the most common cause of premature aging of running rigging. Bad sheet leads or afterguys chafing against life lines, lines running over metal such as the bottom of the boom or against the cap shrouds, or halyards rubbing against the leading edge of the spreaders for extended periods of time are common chafe points. There are numerous others. The most common solution is to periodically inspect all of your lines in use.
During a number of the Whitbread Round the World Races, crewmembers would routinely check all lines at least every three to five hours, making sure to check points where the line touched any other object, and halyards were eased or taken up an inch or two to change the loading points along the length of the line. Chafe can even affect lines on a microscopic level. Repeated soaking in salt water and drying without rinsing in fresh water can allow salt crystals to chafe the fibers. And a high salt content can add both to a higher moisture retention and to early retirement for your lines.
The working load on running rigging should rarely if ever exceed one-fifth of its breaking strength. Manufacturers will list the breaking strengths of their particular lines, and the working load can be roughly calculated using the following formula: sheet load in pounds = 0.00431 x A x V squared. "A" represents the sail area in square feet, and "V" represents the wind velocity in knots. So if a 600-square foot sail was expected to be used in 20 knots of wind, the working load on the sail would be about 1,034 lbs. The manufacturer's listed breaking strength for the particular sheet in use should be at least five times that figure. Of course, there are individual variations to this calculation. The use of a low-stretch material in the sail, such as Kevlar or Spectra, would increase the loads expected in the rigging especially during shock loading.
Physically checking the entire line may not always be practical, especially at the masthead. And if a halyard is over-hoisted, the line at the thimble can easily become worn and fatigued as it constantly flexes on the same point at the masthead sheave. Halyards should be marked at the winch to indicate its maximum loaded hoist, realizing that if stretchy line has been used, that mark will move under varying loads and over time.
Sheaves can provide other hidden problem sources. Sheaves are designed for particular types of running rigging. To minimize the possibility of failure in the rigging, halyard sheaves need to be properly sized to the line, with the sheave diameter being approximately six times the rope diameter. If wire is being used, the sheave diameter should be approximately 20 times the wire diameter for 7 x 19 wire. If 7 x 7 wire is being used, the sheave size should theoretically be double that. Additionally, the profile of the sheaves varies as to the intended type of running rigging. Sheaves intended for use with wire will have a V-shaped outer-diameter profile or a notched groove. Sheaves for polyester rope should have a U-shaped profile, but high-modulus line requires a flatter, wider bottom of the U profile. The wider base gets the fibers to lie more alongside each other, putting the load more equally on all fibers, not just the outer fibers as the rope runs over the sheave. Sheaves designed for use with both rope and wire will have a U-shaped profile with a notch in the bottom of the U to accommodate and support the twisted wire. Twisted wire retains its strength when the rigging bundle is supported in a circular cross section. High-tensile, parallel-stranded line is stronger when laid flat over the outside perimeter of the sheave. In any case, notched sheaves that had been used for wire should not be used for rope when the rope will pass over the sheave while loaded. The sharp notch will quickly wear the rope's cover and cause damage to the line.
Splices and knots can weaken lines depending on the type of the line, the type of the knot and the quality of the splice. Line becomes significantly weaker in a knot because the outer strands in a bend are forced to carry most or all of the load while the inner strands take little or none of it. A bowline knot can reduce the strength of the rigging at the knot by as much as 55% for high-modulus line and as much as 30% for polyester line. An inside clove hitch reduces it less and a fisherman's knot less than that.
By using fisherman's knots to tie high-tensile halyards to their shackles, many of the large French multihulls have found that the strength of the system is quite high while consuming less line than in a splice. That practice requires the line to be over-strength since more strength is retained in a properly executed splice. When the knot begins to deteriorate, however, the shackle can be untied and the halyard switched around, end for end, and the shackle retied without any loss of halyard length. When the knot again deteriorates, the halyard can be cut back one foot and the shackle again retied. Much less line is consumed than by cutting back the entire length of an eye splice. The weakened area can be cut back more times before the halyard is too short for use, lowering the overall lifetime cost of the halyard.
While it can be assumed that a properly executed splice can retain up to 85% of 90% of the line's strength when spliced around a traditional shackle bale, it is also suggested that lock stitching the splice along the length of the bury will help to completely eliminate any possibility of slippage. The bury in a rope splice (the area of the splice that contains the overlap) should be about 30 rope diameters for polyester line and about 80 rope diameters for high-modulus line.
If a properly executed eye splice fails under excessive loads, it is often at the base or head of the eye, so that is the area that should be most carefully monitored to detect premature failure.
Wire for halyards?
Wire for use in halyards may have a few advantages over some types of rope. Its strength per unit of weight is higher than Dacron, and its cost for a given strength is lower than for the more exotic synthetic line. There are, however, a number of considerations that should be addressed. When used as a halyard, the wire's length should be accurately sized. At least three or four wire wraps should be allowed on the winch drum before the start of the wire-to-rope splice for a rope tail. The distance from the winch drum to the cleat should then be long enough to accommodate the splice so that the rope alone is standing on the cleat. If the rope tail is allowed to stand on the winch drum because the wire is too short, the main halyard has been reefed, or a smaller headsail is being used, there will be an increased probability of the line failing at the splice. A properly executed splice can be expected to retain at least 85% to 90% of the breaking strength of the line's weakest component. But that is assuming little or no degradation in either of the components. Some rope, such as Kevlar, doesn't hold up well in abrasion, so a wire-to-Kevlar splice can tend to degrade over time as the wire bury chafes the fiber.
Many of these considerations can be overcome with some forethought. Head pennants can be installed on all of the smaller headsails, providing them with a uniform halyard setting. Wire and splices wouldn't be bent around cleats. There would never be any "sailing on the tail," and wire-to-rope splices would be executed by professional riggers.
Static loading points, such as halyards running over masthead sheaves, may not be a problem with steering cables, but corrosion or broken wire strands may be, so inspection of steering equipment is of paramount importance. Check the wire at the terminals, eyes, and around the sheaves in particular. Inspect the wire for corrosion or rust deep in the inner strands. Edson has introduced a rope steering system that will eliminate some of these problems, but inspections should still be carried out to look for possible signs of failure at the base of any eye splices or chafe around quadrants and sheaves.
Soft eyes (eyes spliced in without thimbles) tend to point load at the outermost end of the line. Thimbles come in a variety of materials and shapes: galvanized, stainless steel, and plastic, designed for wire or rope. The wire thimble will have a higher "lip" along the outside diameter to help maintain the wire's shape, while the rope thimble will have a flatter profile. Although metal thimbles may seem somewhat more durable, nylon reinforced, closed-ended thimbles with webs can be very tough as well. If a metal thimble fails under load and cracks at the outer end, the sharp edges may cause the line to be cut. A plastic thimble, somewhat lighter and perhaps more suited to use in halyards on some boats, may fail under excessive loads or with extended use, but, unlike a shattered metal thimble, the line may survive until a new thimble can be installed.
In some applications on larger boats, a bridge or bar welded inside the thimble may be needed to help maintain the shape and strength of the thimble. Of course, the shackle should be put in place inside the thimble and the bridge welded prior to splicing the line, or the line will be damaged in the welding process. Boats over 48 feet should consider bridging the thimbles for the afterguys, as an example.
In order to get the most reliable service from the vessel's running rigging, the attachment points need to be reliable. It's of little benefit to have the appropriately sized line, correct sheaves and thimbles, if the padeye holding a foot block pulls out of the deck.
Padeyes and cleats need to be installed so that they are in alignment with the direction of the load. If they are out of alignment, they are not capable of handling their maximum load. Rope clutches and jammers also need to be properly aligned with the line. If they are not in clear alignment, side loading of the rope clutch results in a weaker installation, and chafe is increased on the rope cover, leading to possible line failure. Most jammers are not suitable to hold loaded line for extended periods of time.
Understanding the uses and misuses of your lines as well as how to care for them will lead to longer life. Fewer failures can be both more cost-effective and help keep you voyaging instead of in port making repairs.
A four-time Whitbread Round the World Race veteran, Bill Biewenga is a writer, professional race navigator, and yacht captain. He lives in Newport, R.I.