Taking the chafe, jerk, and squeak out of dock lines
Dock lines are subjected to stretch and motion with every wave and gust of wind that hits your boat. This can result in lines wearing out, causing noise, and allowing unwanted motion. In this article, I’ll show you some common approaches to dealing with these problems and tell you my personal favorite solution.
Dock lines are almost always made of nylon. This plastic is strong, durable, and moderately stretchy. Nylon is strong stuff, but millions of cycles of rubbing against other objects will saw through the rope, a phenomenon known as chafe. In many applications aboard, such as for halyards, stretch is the enemy, but for dock lines, you want some give so that the motion of your boat doesn’t jerk the cleats right out of the deck. Chafing sometimes has another, lesser consequence: it makes an annoying squeaking sound. During the day, this noise is merely annoying, but if you’re trying to sleep aboard, it can be maddening. All three of these problems are closely related, and thus have intertwined solutions.
Nylon ropes used for dock lines typically come in two constructions: three strand and double braid. As you might imagine, three-strand line consists of three strands of nylon tightly wound around each other in a helix. Double-braid line, also as the name suggests, consists of a braided outer shell and a separate, braided inner core. Three-strand line is stretchier, easier to splice, and generally less expensive than double-braid. However, double-braid is around 5-20% stronger for a given diameter, and many boaters find it more pleasing, both to the eye and the hand. It’s probably the most common dock line type in use today.
Very large vessels may use more esoteric rope constructions I’m not going to discuss in this article, but there is one other material that will feature prominently as we go forward. Ultra-high-molecular-weight polyethylene (UHMWPE), more commonly known by its trade names, Dyneema and Spectra, is extremely strong, low-stretch, low-friction, and abrasion-resistant. These qualities allow it to be used in place of steel in some applications, such as standing rigging and shackles.
Chafe Guard 🔗
The first step up from a plain ol’ nylon line is to add some material at the points where it rubs against other objects. This can be almost anything (and sailors get creative) as long as you attach it to the line itself. You don’t want the line moving inside the guard, because then your line will chafe against the guard instead of the thing you were trying to protect it from.
Traditionally, the line was wrapped in leather secured in place with whipping twine. Another common remedy is to reeve (insert) the line through a piece of hose. But you’ll probably get more mileage out of purpose-made products, such as woven polyester sleeves. Some of these products feature a hook-and-loop fastener both to hold the material closed around the line and to grip the line itself, which allows them to be installed over lines that are in use.
This type of chafe guard may reduce the squeaking noise of the line sliding over the chock or gunnel, but it still has a fair amount of friction and does nothing to reduce the motion, so odds are you’ll still have some noise.
Sometimes the motion of the boat is just too violent for the amount of stretch in the lines. The jerking could loosen your deck hardware and in extreme cases rip it right out. The motion could also be uncomfortable while on board – I’ve been nearly thrown out of bed by the sudden stop at the end of a too-firm dock line. Insufficient stretch is particularly a problem with double-braid line, but also with oversized three-strand or just unfortunate circumstances. The solution is to add a snubber, which is a stretchy device added onto the line. Critically, the dock line remains continuous through the snubber so that if the snubber fails, your boat won’t break free – it will just have a looser dock line attached to it. Snubbers come in several flavors, most commonly rubber “sticks” the line is wound around, or elastic with shackles on each end that are clipped to knots in the line.
In most cases, if you use a properly-sized three-strand line, you won’t need a snubber. But in the cases you do, I prefer the rubber stick type because they don’t require knots in the line. (Knots reduce strength.) I do like the elastic-shackle type for use with all-chain anchor rode, because the shackles make for easy attachment to the anchor chain with no effect on the chain’s strength.
UHMWPE Loops 🔗
Most people don’t attempt to use dock lines entirely made out of UHMWPE because the lack of stretch severely exacerbates the dangerous and uncomfortable jerking motion. But it would be really nice to have a stretchy nylon line with just a bit of stretch-free UHMWPE near the boat end, so the line won’t stretch over the chock and produce the dreaded squeak. Indeed, I’ve heard superyachts sometimes have hybrid lines of this type, but I haven’t been able to find any mention of them online, so apparently this technology hasn’t filtered down to the recreational market. The next best thing is to make a loop of UHMWPE, cow-hitch it to the eye of your nylon dock line, and loop it over the cleat. The loop provides the last foot or two of length, where its wonderful properties really shine in resisting chafe and preventing squeak.
This is a truly great solution and I’ve never heard of it causing a problem. But in theory the cow hitch concentrates the stress onto a tiny section of the nylon rope, and that makes me nervous. Just as with the snubbers, I want a single, continuous line from the dock to my deck cleat to minimize failure points.
UHMWPE Sleeve 🔗
One of my rigger friends turned me on to this neat sleeve form factor of UHMWPE. It’s easy to slide over the line. It can be used in the same places as normal chafe guard. UHMWPE cannot be fused with heat, so a whipping is the most practical way to prevent it from fraying and secure it in place. In addition to providing excellent chafe protection, it is slick enough that it doesn’t make any noise when it moves across the chock. And the nylon line is continuous, so if anything were to happen to the sleeve, the boat is still secure.
Putting It All Together 🔗
As you’ve probably guessed by now, my preferred solution is a three-strand nylon dock line fitted with a UHMWPE sleeve. I splice the eye for the specific cleat the line will be used with. I whip the end and the UHMWPE sleeve with color-coded twine so that it’s easy to tell crew members which cleats go with which lines. I haven’t found any need for a snubber with this setup.
Assuming an average wave period of 8 seconds, your boat will be subjected to 1 million waves about every 3 months. ↩︎
Pun intended ↩︎
Based on my informal survey of data from several manufacturers ↩︎
I prefer to put the eye on the boat and the other end on the dock in most cases, but that’s a topic for another article ↩︎