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Safe Boat Operations – Line Handling and Care

Marlinespike is the art of handling and working with all kinds of line or rope. It includes knot tying and splicing. Knowledge of line handling terminology, phrases, and standard communication is important to operating a boat safely in all docking situations.

The uses for a particular line will depend heavily upon the type and characteristics of the line.

Lines are made of natural or synthetic fibers twisted into yarns. The yarns are grouped together in such a way as to form strands. Finally, the strands are twisted, plaited, or braided, in various patterns, to form line.

Line used on most boats is classified in two different ways:

  • Material used.
  • Size.


No matter what the line is made of (natural or synthetic), it is measured the same way, by its circumference or distance around the line.

Synthetic fiber line is made of inorganic (man-made) materials. The characteristics of synthetic fiber line are considerably different from natural fiber line. The differences will vary depending on the type of material from which the line is made. The most common types of synthetic line used on boats are nylon and polypropylene. Because of its superior strength and elasticity, nylon is used where the line must bear a load.

The use of a hot knife is the preferred method for cutting nylon and polypropylene line. Using a hot knife eliminates the need for burning the ends. Some soldering irons can be fit with blades for cutting line. One of the more common methods is to heat an old knife or scraper using a propane torch.

Proper maintenance and inspection of line is vital to the safety of the boat and crew. If a line is damaged or not properly maintained, it could fail, resulting in possible damage to property and/or injury to personnel.

Aging affects natural fibers more severely than synthetic. Cellulose, the main component in natural fibers will deteriorate with age, getting more brittle and turning yellow or brownish. When used with bitts or cleats, the fibers easily rupture and break. Aging is not a significant problem for nylon line, though it will change its color with age. Polypropylene line does deteriorate rapidly when exposed to sunlight and must be checked regularly.

Damage to internal natural fibers occurs when a line under a strain exceeds 75% of its breaking strength. Although this load is not enough to part or break the line, it is enough to cause some of the internal fibers to break. Internal fiber damage indicates aging and internal wear. Internal broken fibers indicate that the line has been damaged. With synthetic line, some of the individual synthetic fibers of the line may break if overloaded. These will be visible on the outer surface of the line.

Chafing is wear affecting the outer surface of a line, caused by the friction of the line rubbing against a rough surface. To check for chafing, the outer surface of the line should be visually inspected for frayed threads and broken or flattened strands. With synthetic line, chafing can also cause hardening and fusing of the outer layer.

Cutting damage found on line is similar to chafing, but occurs when the line rubs against a sharp edge rather than a rough surface. This will give the appearance as if the line was cut with a knife. Cutting damage to yarns and threads will greatly reduce the effectiveness of the line and can cause failure under strain.

Signs that a line was overloaded are elongation and hardness. Line stretched to the point where it will not come back has a decreased diameter. To determine this, you should place the line under slight tension and measure the circumference of a reduced area and of a normal area. If the circumference is reduced by five percent or more, the line should be replaced.

Another indication of synthetic line overloading is hardness to the touch. This can be noticed while gently squeezing the line. Overloaded line shall not be used.

A line under strain is dangerous. If it parts (breaks), it will do so with a lot of force, depending on the size and type of line, and how much strain it is under when it parts. As a general rule, when a line is under stress, it is important to always keep an eye on it. Standing in line with the strain may cause serious injury if the line parts and snaps back.

Prior to each use, all eye splices should be inspected on all working lines (towline, anchor rode, mooring lines, etc.). Boat owners should pay particular attention to the area of the line that is tucked back in onto itself, ensuring there are no “flat spots” or areas where the inner core has slipped away leaving only the outer cover. The entire eye should be inspected for chafing and cuts.

While there is nothing that can be done to restore bad line, precautions can be taken to extend the life of lines. Proper use and care will significantly extend the lifetime of the lines used. Everyone should be responsible for protecting lines from damage.

Lines should be kept free from grit or dirt. Gritty material can work down into the fibers while a line is relaxed. Under tension, the movement of the grit will act as an abrasive and will cause serious damage to the fibers.

Chafing gear can be made of old hoses, leather, or heavy canvas. It is used to protect short pieces of line where they run over rails, chocks, or other surfaces.

Line chafing diagram

Bitts, cleats, and chock surfaces should be kept smooth to reduce line abrasion. You should ensure that water does not freeze on lines. Ice is abrasive and can cut fibers. You should avoid walking on, placing loads on, dragging loads over, or in other ways crushing or pinching a line. If a line has to go around something, a fair lead should be used. A fair lead is any hole, bull’s-eye, suitably placed roller, sheave, etc., serving to guide or lead a rope in a desired direction.

To prevent the deteriorating effects of sunlight, chemicals, paints, soaps, and linseed or cottonseed oils, lines should be stored to prevent contact with harmful items or conditions.

By following these recommendations you will be able to lengthen the useful life of your boats lines.