Polyester is widely used for boat lines and for sail material because it combines good strength and durability, relatively low stretch and reasonable prices.
Polyester fibers are very fine and hair like, typically about 0.023 mm dia. These fibers are almost always white. It is virtually impossible to distinguish between nylon and polyester by appearance alone.
Polyester Physical Properties
Polyester has a specific gravity of 1.38 which means it does NOT float.
Polyester is very strong, it has a similar tensile strength to Nylon 6, and is slightly stronger than regular Nylon.
Unlike Nylon or Polypropylene, Polyester is not stretchy. Usually any stretch present in Polyester is minimized by pre-stretching during the manufacturing process. It also has low creep under load.
Unlike Nylon, Polyester retains its strength when wet.
Melting Point 240 degree Celsius. Varies with different composition.
UV resistance is Excellent. Typically a polyester rope will only lose 10% of its breaking strength after 2 years of outdoor use. This is excluding cuts or severe abrasion.
Polyester is often chosen as the outside coating for a cored rope made from a stronger but UV sensitive materials such as Kevlar.
Excellent abrasion resistance
Polyester is non conductive to electricity
Strength and Weight of Polyester Rope
Diameter
Weight
Average Strength
Inches
mm
Lbs. per ft
Kg per m
Pound
Kilogram
3/6
4.8
0.01
0.02
1175
533
1/4
6.4
0.02
0.03
1088
2400
1/3
7.9
0.03
0.05
3400
1542
3/8
9.5
0.05
0.07
4800
2177
4/9
11.1
0.06
0.09
2993
6600
1/2
12.7
0.08
0.01
9000
4082
5/8
15.9
0.13
0.19
15500
7037
3/4
19.1
0.18
0.27
18000
8172
1
25.4
0.32
0.48
32000
14528
Polyester Chemical Resistance
Good resistance to Alkalies and Acids at room temperature. As the temperature increases, the resistance decreases.
Polyester has excellent resistance to petroleum based products, bleaches and solvents. That doesn’t mean it is not affected. Don’t soak your lines or sails in strong bleach for long periods, they will be weakened.
Advantages and Disadvantages of Polyester
Advantages
Good chemical resistance at regular temperatures
Excellent UV resistance
Polyester is slightly stronger than Nylon
Unlike nylon it does not lose strength when wet
Low Stretch
Stiffer than Nylon
Well suited to Static Loads
Well priced and widely available
Disadvantages
Polyester does not float.
Some braids of polyester are quite stiff and don’t work very well in blocks.
Polyester is not suitable if the load is subject to jerking. It does not give as nylon does. In these applications it might only be used as the outside protective layer.
Polyester Uses
Among the conventional synthetic ropes available Polyester has the lowest stretch and best abrasion resistance, combined with good UV resistance.
It is commonly used for halyards and sheets.
Polyester is the most common readily available sail material.
The fabric is treated to improve rigidity and resistance to UV.
It is often referred to as Dacron™ or Terylene™.
It also finds use for anchor rode. It is stiffer than nylon and not as stretchy.
There have been cases where nylon anchor lines have failed because high temperatures have been generated during strong weather, particularly when it’s hot. This caused the nylon anchor/mooring lines to soften and fail.
Polyester rope or polyester combinations are often found for winches, capstans and block and tackles. Its low stretch and low creep.
It is extensively used for cargo lifting straps, tow straps, and slings, where a stretch and bounce effect could destabilize a load.
There are a number of ropes offered that combine polyester outer braid with nylon inner core to get the low stretch and resistance to wear of polyester with the cushioning effect of nylon. It helps control the stretch of nylon in some climbing ropes.
It is also combined with aramids again to provide protection and wear-ability in the outside layer, while the core provides more strength. Many such ropes are marketed as survival rope.
The safe loading of a rope is a 1/10 to 1/12 of its breaking strength. Remember that knots weaken a rope as does age, wear, chemical attack etc.
NOTE:This information is for general knowledge. If you have a critical application check your requirements and make sure the rope is suitable. Different manufacturing processes change the feel, appearance, and strength of ropes so the strength figures I am giving are for comparison only. Some ropes have been coated with materials that improve handling or resistance to sun or chemicals. If you clean them harshly this coating could be damaged. Follow the manufacturers advice for care and handling.
