Lines, halyards and ropes (1/3) - Moorings

Nicolas Venance - Boat Technical Journal

What are the characteristics of mooring lines on pleasure boats? How are they made, and how can we optimize their lifespan? Today's program features a not-so-simple item: the mooring line!

When a moored boat is tossed about by waves or wind, very considerable forces are at play.
Do not tie up a heavy boat with a halyard or sheet, as this could cause damage.

The qualities of a good mooring line

Indeed, sheets and halyards have a very low coefficient of elongation (elasticity), unlike mooring lines, which can stretch from 10% to over 25 % of their length under load.
This is why a good mooring line is elastic, relieving the stresses transmitted to the fairleads, cleats and other winches securely mounted on board.
It's also flexible so it's easy to handle, even when salted, and UV-resistant.

With regard to diameter, it's customary to add "4" to the boat's length in meters to deduce the diameter of the mooring lines in millimeters. An 8-m motorboat will thus be fitted with mooring lines with a diameter of at least 12 mm.

On the subject of length, with 4 mooring lines on board (two short ones the length of the boat and two long ones of one-and-a-half or two lengths), you can cope with almost any situation. Add to that a fifty-metre webbing drum, and you're all set!

What type of mooring lines?

Those made of polyamide -nylon- are the most elastic.
On the other hand, in terms of abrasion resistance and cost, polyester wins out hands down, but offers a lower modulus of elasticity.
Polypropylene mooring lines float, but are less resistant to abrasion and UV rays.
Last but not least, the classics include mooring ropes made from natural fibers. These are generally made from hemp or sisal, also used for... flooring.
These different materials allow three different ways of building mooring lines.

Stranded mooring lines

Stranded mooring lines are ropes made up of 3 or 8 strands. 8-strand mooring lines can be spliced to form anchor or mooring chains. 8-strand is considerably more elastic than 3-strand.
Stranded mooring lines are easy to splice.

Braided mooring ropes

Using this manufacturing technique, a braid is made using spindles that are themselves braided.

These mooring lines are very flexible and easy to handle, and are highly resistant to abrasion.

Braided mooring ropes

Braiding is similar to making a "scoubidou", unlike stranding, which involves winding fibers into strands and twisting them together to form a cable. 12 to 18 spindles are braided and then protected or not by a sheath.
The first advantage of braided mooring lines is comfort. They don't "cock" (to cock is to make it impossible to coil a rope without rotating it slightly). These sheathed lines are particularly pleasant to handle.

Preserving your moorings

To extend the life of mooring lines, the careful sailor can make or have made sheaths (or over-sheaths for double-braided mooring lines) which will remain in place at the usual mooring points.
These sheaths act as wear parts before the structure of the mooring line is attacked.