Springing a sailboat On and In
Coming into a slip is usually not a problem and does not require a spring because you merely drive the boat using either forward or reverse. Once you are in, you can sort out the details.
Coming up to a Tee-head is more the situation where you need to spring on. The need for accuracy in your maneuver is heightened when the space is tight. Here is an animation of a boat doing this.
And here are the forces and moment diagrams.
In the above scenario, if the wind or current is from behind with any strength at all, you should consider backing into the slot instead.
After you make your plan, ensure dock lines are made ready and (very important) that the crew are told exactly which direction to cleat the boat when they get off. In high winds, things can go south very quickly.
Plan to get the bow of the boat sprung to the dock, and then to spring in.
If you’re going it alone, there is usually quicker access to the dock from the cockpit. Below the skipper steps off, taking the amidships spring line to the dock, then powers the boat around using the spring line. The spring line at amidships provides extra distance between the forces and, thus, an extra turning moment.
