When sailing it’s important to have sheets and halyards that are strong and do not stretch much. This allows you to effectively and reliably control sail trim. However, when alongside, using a spare sheet or halyard to moor your vessel would be a mistake!
Mooring lines need to be strong - yes. But they also need to be able to stretch. A mooring line that doesn’t stretch will make for a very uncomfortable night’s sleep and may even cause damage to deck gear and cleats.
Mooring lines are usually made from relatively inexpensive man made polyamide lines, perhaps with a soft, polyester cover. They stretch well and stand up to UV light and chafe. You might also consider splicing bowlines in one end, for the shore, and sheathing the line with leather to reduce chafe.
Mooring lines are chosen by diameter and length based upon the weight and length of the vessel concerned. As a rule of thumb, some suggest the following;
|Vessel’s Hull Length (ft)||Line Diameter (mm)|
Of course, if your vessel is heavier than the average for her length then it’s advisable to go up one diameter size, just in case.
Bow and stern lines should, as a rule of thumb, be at least ½ the boat’s length. Spring lines should be at least the length of the boat. This allows for adjustment, especially when alongside a harbour wall in a tidal area. At least one additional long line is useful for when extra mooring lines are required or you need a tow.