We have been using the same set of Yale Ropes high modulus dock lines coming onto four years now. These 11mm (7/16″) ropes are as strong as our normal 24mm (one inch) polyester, weigh a fraction of the latter, and are less prone to chafe. And they are obviously a lot easier to handle.
When we started out with these we assumed that we’d use them to get the boat secured and then switch to heavier polyester. However, except for two situations, this has not been the case. The first is when we are in storage mode, leaving the boat for long periods of time. In this case there is no benefit to using the higher strength and more expensive cordage. The second is when docked with a surge. The high mod materials have little stretch and in some case transmit an uncomfortable snub to the boat. In both cases we switch to a “brait” style polyester.
Take a look at the outer cover chafe above. This occurred during a fueling stop in Pango Pango, American Samoa in 2005. The edge of the fuel barge was sharp concrete, and the spring lines were laying across this surface with a four foot (1.2m) swell running under our hull. The polyester cover was damaged, but the inner high modulus material was barely affected. We are still using these dock lines.
If you are cruising on a yacht of 50 feet (15m) or more, high modulus dock lines may be worth considering.
A final point. We use bowlines for knots. These are left somewhat lose, as shown in the first photo. If a conventional tight bowline is employed we have found these work themselves tighter to the point where they can be impossible to untie.