Safe Boat Operations. Docking Maneuvers. Mooring and Spring Lines.
Source: Mariners Learning System
Before using mooring lines to help maneuver at the dock, crew members need to first know their names and what they do:
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The bow line (#1) and stern line (#4) are used to keep the vessel secured to the dock.
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The after bows spring (#2) and forward quarter spring (#3) are used to keep the vessel from surging forward or aft at the dock.
Docking line diagram
Normally, only these four lines are required when mooring. During times of foul weather, breast lines (#5) may be used to provide additional holding strength. Fenders should be used at strategic points along the hull to prevent chafing against the dock or float.
If it becomes necessary to hold position alongside a dock, but swing the bow or stern out in order to clear another vessel or obstacle, using a spring line can help to accomplish this.
The forward quarter spring, or stern spring (#3) should be used to “spring out” or move the bow away from the dock. By backing down on a boat’s engine with just the forward quarter spring attached to the dock, the bow will move away from the dock.
The after bow spring, or bow spring (#2) should be used to “spring out” or move the stern away from the dock. The stern will move away with the rudder full toward the dock and the engines ahead. With the rudder turned the other direction or away from the dock, the stern will move towards the dock or “spring in”.
The boat operator and crew should never attempt to fend a boat off a pier, float, etc., by hand or by foot, but should always use a fender. The proper sized fenders should be kept at hand.
When mooring with an off-dock wind, the approach should be made at a sharp angle – 45° or more and the approach should be made parallel with the intended berth and the fender should be rigged in appropriate positions. The boat operator should ensure that the boat has no fore and aft movement when contacting the dock.
Except for using the forward quarter spring, the stern of a boat should never be tied down while maneuvering beside a dock. This restricts maneuverability.
The pivot point of a boat is approximately one-third of the way aft of the bow when the boat is underway at standard speed. This point moves forward as speed is increased and aft as speed is decreased.
The greatest amount of control over the boat is gained by maneuvering into the prevailing face of the wind or sea. Boats turn more slowly into the wind and sea than away from them. A single-screw boat will generally back into the wind when the boat has more “sail” area forward of the boat’s pivot point than aft.