Springs are mooring lines that run diagonally fore and aft between the boat and the pontoon. They stop the boat surging forwards and backwards along the berth, while the bow and stern lines hold her ends in.
A boat lying alongside a pontoon is usually held by four lines:
- The bow line runs from the bow forward to the pontoon, and holds the bow in.
- The stern line runs from the stern aft to the pontoon, and holds the stern in.
- The springs run diagonally. One runs from near the bow aft to the pontoon, and the other from near the stern forward to the pontoon, so they cross or lie roughly alongside each other.
The bow and stern lines mainly stop the boat moving away from the pontoon. The springs stop her moving forwards and backwards, surging along the berth with the wind, the wash of passing boats or the tide. Without springs a boat tied only at the bow and stern moves about, rubs her fenders and snatches at her lines.
Names vary between sailors and books. Some call the line from the bow aft the forward spring, or the bow spring; others name springs by which way they stop the boat moving. Describing them by where they run, from the bow aft or from the stern forward, avoids confusion.
Springs are also useful for handling the boat:
- When coming alongside, stepping ashore with a spring first and making it fast holds the boat close and stops her while the other lines go on.
- When leaving with the wind blowing you on, a bow spring with the engine ahead swings the stern out, and a stern spring with the engine astern swings the bow out. This is called springing off.
Leave a little slack in the lines so the boat can move gently, with the fenders where they protect the hull. In tidal water, the lines must be long enough to allow for the rise and fall unless the pontoon floats. Check them again if the wind gets up.
More in the book: Chapter 8, Under power, and in the marina