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

Boating NZ - - Contents - BY CRAIG RITCHIE

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.


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.


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.

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