Securing a small boat between pilings in a wrong-sized slip is a common challenge. The dock line angles from the dolphins (outlying pilings) are too narrow for a beam wind, allowing the boat to dance around, increasing forces, chafe, and even making it difficult to stand in the cockpit. During a recent winter near-gale we measured dockline forces on several smaller boats that reached four times higher than the static wind load. If the recommended size dockline was used, the rope would be operating beyond its working load limit in real storms and could fail. Increasing the line diameter would result in more jerking and chafe.
With hurricane season ramping up, many of us are going over our rope inventory, making sure we have more than enough lines to secure the boat. Chafe gear fights external friction on our lines, but how do we combat internal heat build-up? Dock lines are particularly susceptible to overheating. If the boat is exposed to short-period chop from the side, the frequency can be high and the force can exceed the 10:1 safe working limit, and even with rain or spray to cool the rope there may be significant weakening due to internal friction.