Learning the ropes
The dock line is the only thing keeping your boat from floating away. Would you trust your pride-and-joy to a cheap rope from the discount store? Amazingly, many boaties do just that. Here’s the line on dock lines, and how to give your boat the protection
Not all mooring lines are created equal.
Just for fun, next time you’re walking along the marina dock check out how many pricey boats are secured with budget ropes. Truth is, there are precious few marinas anywhere in the world where you won’t see at least a few big-money boats tied up just like this. And in many cases this situation arises from simple ignorance. After all, a rope is a rope is a rope – right?
Not exactly. Like so many other things in life, rope comes in a huge variety of types and styles. But not all of them cut it as dock lines. Taking a few minutes to learn the differences between them allows you to choose wisely – no one wants to be that guy whose boat broke free in the storm and damaged everyone else’s.
Ropes are made from a wide variety of materials, but most common are manila, polyethylene, polypropylene, polyester and nylon. Each has its pros and cons.
With its dull-brown, hairy appearance, Manila rope is fairly easy to spot. A hard, natural fibre, it’s strong, doesn’t stretch much and holds knots reasonably well. And as a natural fibre, it won’t melt when subjected to heat or friction as synthetic ropes sometimes will. It’s also surprisingly resistant to sunlight.
The downside – and it’s a huge one – is that it simply doesn’t last around water. Put it away wet and it will mildew overnight. Exposure to chemicals like oil or petrol will only accelerate that process.
Fortunately, most of the manila rope you’re likely to find in a marine store today is sold as decorative material for nautically-themed bars and restaurants. In recreational boating, it’s been completely replaced by synthetics. If you see this stuff in actual use, it’s only because the person who bought it simply didn’t know better.
A staple of rural petrol stations and suburban discount stores, the familiar bright-yellow polyethylene rope is the least expensive synthetic cord sold in the world today. Where boating is concerned, it’s most frequently seen tied to home-made anchors that someone created by filling an old paint can with cement.
The biggest knock against polyethylene line is that it’s wiry, so the stuff tangles like crazy. And heaven help you if you ever get a fishing lure accidentally snagged in it – even pliers won’t help. Though it works fine for toys in a swimming pool, polyethylene rope has no place on a boat. Beyond its tangling issues, polyethylene degrades very quickly with exposure to sunlight. This makes it a terrible choice for dock lines that sit out in full sun all day.
Among the most widely-used type of rope on boats, polypropylene is also relatively inexpensive and available in a wide variety of sizes, in both three-strand and full-braided versions. The fact polypropylene rope floats like a cork makes it ideal for ski-tow ropes, or for heaving lines. It’s also perfect for securing tenders or dinghies, since any excess line that falls into the water isn’t likely to become snarled in the boat’s props.
Polypropylene rope doesn’t absorb water, it doesn’t shrink when it’s wet, it holds knots securely and it remains flexible regardless of the temperature. And like all synthetic ropes, it comes in a rainbow of colours so you can match the boat’s décor.
It’s often used as dock line, but it’s far from ideal for the task. The two big strikes against polypropylene are: it’s not terribly strong compared to other synthetic materials and, it doesn’t have much stretch.
A polypropylene rope of a given diameter is only about half the strength of a similar nylon or polyester line. Combined with its relatively low elasticity, that means polypropylene lines will snap long before others will, making it a poor choice for high-stress jobs like dock lines or anchor rode.
Like cheaper polyethylene, polypropylene ropes also degrade quickly with exposure to sunlight, so if you use them as tow ropes or heaving lines, be sure to stow them in a closed compartment where they’ll be protected from UV rays.
The other issue with polypropylene is that the stuff has a fairly low melting point, so it doesn’t work well for jobs where it will encounter friction. The fibres will either soon abrade, or melt together as if glued.
Polyester’s lack of elasticity makes it a poor choice for dock lines.
Once the darling of 1970s fashion designers, polyester has really found its niche with rope manufacturers. You’ll never see this stuff at the discount store, but upscale marinas catering to sailors usually stock polyester line since it is quite strong, remains pliable at a range of temperatures, doesn’t stretch and doesn’t shrink when wet – attributes that make it absolutely ideal for sailboat rigging.
Although it’s incredibly strong, polyester’s lack of elasticity makes it a poor choice for dock lines, since any stress from wind or wakes will transmit directly up the line and straight into the boat’s cleats. For the same reason, it’s also a poor choice for applications where it will be subjected to any kind of shock, such as towing another disabled boat.
HIGH MODULUS POLYETHYLENE
Remember those cheap polyethylene ropes from the discount store? Meet their steroid-enhanced secondcousin – high modulus polyethylene, which is ounce-forounce the strongest, toughest fibre in the world.
Known by a host of trade names including Dyneema and Spectra braid, high modulus polyethylene is all the rage with fishermen, since fishing lines made from the stuff offer tremendous strength and abrasion resistance, yet are so thin the fish can’t even see them. Weave the stuff up to boat rope diameter and you have a line strong enough to tow a bus.
Like polyester ropes, high modulus polyethylene has zero stretch, and is made primarily for rigging in high-end racing sailboats. You’re not likely to find it at the local marina, but if you do, you’ll be able to spot it by price alone. Look for it to be displayed in a locked case, and probably adjacent to a defibrillator.
Representing an almost perfect balance of strength, flexibility, durability and stretch, nylon rope reigns as the undisputed king of dock lines. While it does cost more than some other types of rope, this is one instance where you really do get what you pay for.
Nylon line comes in sizes ranging from about the diameter of a pencil to about as thick as a beer can, in both three-strand and fully-braided versions. Both
Nylon absorbs shock – greatly minimising the strain transmitted to a boat’s cleats.
varieties hold knots well and maintain their knot strength when wet. Nylon lines are also highly resistant to oil and petrol, so a dunking in the bilge won’t harm them one bit.
Although nylon rope doesn’t float like polypropylene, it offers the kind of brute strength few other materials can match – steel cable included. And while nylon line will absorb some water, it remains comparatively elastic no matter how wet it gets. This unique quality makes the stuff absolutely ideal for highstress applications like emergency tow ropes, as anchor rode, and as dock lines.
Nylon has an extraordinary ability to absorb impact from a boat rocking in the breeze or bouncing from careless wakes, greatly minimizing the strain transmitted to the boat’s cleats. It offers tremendous weather and abrasion resistance too, so it can take a beating month after month without losing its shine.
When shopping for dock line, look for 100% nylon ropes. Nylon is sometimes blended with other materials to reduce cost but for dock line, spend the extra dollar and buy the pure nylon stuff.
Having narrowed down the material, the next step in selecting a dock line is choosing the correct size.
The rule of thumb is to use the largest diameter line you can get through your boat’s cleats. Half-inch (13mm) line is probably the most commonly used on pleasure boats, followed by five-eighths (16mm). The cost difference as you go up from one size to the next is minimal, so buy the strongest line you can fit through the cleat. When that inevitable wind storm comes along and the waves are pounding in, you won’t regret having a stronger line.
Apart from diameter, the other size consideration is to ensure your lines
are long enough. Always buy lines that are at least the same length as your boat. The last thing you want is to travel to a new marina and find out that your dock lines are 300mm too short.
TWISTED OR BRAIDED?
Ropes come in two basic styles, twisted or braided. Twisted rope is formed by coiling three individual strands together in the same direction, and opposite of the direction of the individual strands themselves. This keeps the rope from unraveling and prevents it from curling excessively.
Braided rope has its strands wrapped against each other in an overlapping pattern. Solid braid rope is manufactured by tightly wrapping several lengths of yarn together, and may be constructed from four, eight, 16 or 32 individual pieces (subsequently called four-, eight-, 16- or 32-plait rope). Solid braid rope is consistently firm to the touch and almost perfectly round in profile, so it’s a better choice if you need to pass it through any pulleys or winches.
Neither style offers appreciably more strength than the other. Quite honestly, the biggest difference is cosmetic so choose what you feel looks the best.
It’s important to check dock lines periodically for nicks, knots, frayed spots or kinks, all of which can seriously impair their strength. Replace any suspect-looking lines before they cause you problems.
With normal wear and tear, dock lines generally last from one to two years. Exposure to sunlight will shorten the life of any line, as will repeated exposure to stress – if your boat is exposed to consistent wave action or a steady current, the line won’t last as long.
If abrasion from rubbing against the dock or the boat’s rub rail is an issue, use chafe guards to protect the lines and extend their service life. The best ones are those made from leather or fire hose, which shed both water and heat far better than cheaper plastic types. It’s usually a good idea to carry an extra dock line or two someplace onboard. That way, should one snap while you’re on the water, you’re able to replace it right on the spot. It’s kind of like having a spare
tyre for your vehicle.
Everyone likes to save money where possible. But dock lines are one area where it’s worth spending a tiny bit extra to get the very best. Given that they’re the only thing keeping your pride and joy from being blown out to sea, the peace of mind that comes with having the right ropes simply can’t be beat.
LEFT AND BELOW There’s no shortage of choice in terms of colour, diameter or material – but do your homework before splashing out on a new set of mooring lines.
ABOVE & RIGHT Polyester rope – it’s incredibly strong, but less than ideal for use as docking lines. BOTTOM RIGHT Polypropylene rope degrades fairly quickly as a result of UV damage – particularly in New Zealand.
ABOVE Rope comes in a remarkable range of materials – but versatility is limited. Choose rope for its intended application.