Choosing the right mooring rope for a Tokyo Bay berth

Mooring lines are easy to overlook until one fails or chafes through overnight. In a tidal berth with a 2-metre range, the wrong setup causes problems that a bit of thought at the chandlery would have prevented. This is what we recommend to berth holders at Arctic Marina.

Material: polyester vs. Nylon ¶

Polyester three-strand is the standard choice for mooring lines in Japanese marinas. It has low stretch, which keeps the vessel positioned consistently in the berth, and it is resistant to UV degradation and abrasion. We sell it by the metre in 16 mm and 20 mm diameters.

Nylon has more stretch, which makes it useful as a spring line or in situations where shock loading is a concern. A berth exposed to wash from passing ferries, for example. It is not ideal as a primary mooring line in a tidal berth because the stretch makes the vessel position less predictable.

Diameter and length for a tidal berth ¶

For a 10-metre sailing yacht, 16 mm polyester is adequate for most conditions. For vessels over 12 metres or heavier displacement, 20 mm is more appropriate. The length of your mooring lines needs to account for the tidal range: in Tokyo Bay, a spring tide of 2.5 metres means your lines need to be long enough to allow the vessel to rise and fall without going tight. A common mistake is lines that are too short, which pull the vessel hard against the pontoon at high water.

As a rough guide, mooring lines in a tidal berth should be at least 1.5 times the vessel's beam in length, and ideally longer for the bow and stern lines.

Chafe protection ¶

Where lines pass through fairleads or over cleats, chafe is the main cause of failure. Wrap the line with leather or purpose-made chafe guard at any contact point. Check the lines every few weeks, especially after a period of strong wind. We have seen 20 mm polyester chafe through in under a week on a poorly positioned fairlead.

Pre-spliced mooring lines can be made up at the chandlery on request. Allow a day or two for the work. Bring your vessel's length and beam and we can suggest the right lengths.