Dock lines are usually made from nylon or polyester synthetic fibres. Polypropylene is occasionally used and although it’s the least expensive and can be useful for temporary applications we don’t recommend it for longer term use. It will need to be replaced more frequently which will cost you more in the long run.
Low-stretch lines, like old worn-out polyester braid on braid used for running rigging are not suitable as they transmit shocks from waves, loading up and loosening dock cleats and your boat's deck hardware.
Polyester isn’t quite as strong as nylon however it doesn’t shrink or weaken when wet and it’s slightly harder wearing than nylon. It also tends to age better and isn’t as prone to UV damage. It isn’t quite as stretchy as nylon though so it doesn’t provide the same shock absorbing protection.
Construction methods used for dock lines include 3-strand, double braid and 8-plait.
3-strand line is easily recognisable with it’s three strands of fibre woven together. It is very easy to splice and is the most affordable. 3 strand is usually available in Nylon, Polyester and Polypropylene.
Braid on braid or doublebraid as it is sometimes known is somewhat stronger for a given diameter, has about half of 3 strand's stretch, and is available in many colors so you can coordinate your dock lines to match the colour of your trim or canvas. It’s a very flexible construction method so the cover and core material can be mixed to give the best of both worlds.
8-plait or octoplait is an 8-strand single braid. Single braids are very supple and limp, so they are easy to coil and handle. 8-plait is frequently the choice for larger cruising boats above 50'. It is harder to splice but is very hard wearing and will last a long time. It’s also commonly used as an anchor rode as it can be spliced onto chain.
In terms of choosing the correct diameter we’ve found that the same general rule that applies to anchor lines also works well for dock lines. We recommend 3mm of line diameter for every 2.5m of boat length and we have converted in the chart below to make it easy to understand.
SIZING YOUR ANCHORING AND MOORING LINE
CHOOSING THE CORRECT LENGTH DOCK LINE LINE
Bow and stern lines should be about two thirds of the length of the boat. Spring lines, used to keep the boat parallel to the dock, run aft from the bow to the dock and forward from the stern to the dock, usually need to be as long as the boat. On our 38 foot cruiser racer we use 10m of 14mm three-strand polyester for the bow and stern, and 12m lengths for the springs, and it's perfect.
We also keep two 14m doublebraid pre-made dock lines onboard. If we take one from the bow cleat to the shore cleat and from there to the centre cleat on the boat we have a bow line and spring taken care of with one rope. We do the same at the stern. They also perform double duty as a tow rope when they are linked together with the nylon core providing good stretch so they are well worth having on board.
If your braided dock lines have become hard and dirty you can make them look like new again by throwing them in an old pillowcase and running them through your washing machine with some laundry detergent and a little fabric softener. Keep the water cool as you can damage the ropes if the water is too hot. Don’t tumble dry them for the same reason!
Chafe is damage caused when lines rub against each other or another surfaces. It can be reduced by crossing lines and being careful how you tie off your cleats. A good tip if your lines are all the same lengths is to rotate them each time you take them off. In this way any chafe is spread across the set. Use chafe protection where surfaces or sharp corners accelerate wear.
If you don’t leave all your dock lines behind all the time consider making up just one line to leave behind. Set the length so your boat always ends up exactly where you want it. No more endless adjusting to get her into the same place every time
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