I too was wondering why you were backing in. Either way in your set up I would attach my bow line to the first outward cleat on the dock and buy one of those aeirel like whips with a curve on the end and place it where your port spring line cleat on the dock is (middle one).
When leaving the slip walk the port bow line back and place on the end of the ariel whip as it hand over the water into the slip, and it so it is ready to grab when you come into the slip. it should already be the correct length so you wont hit your stern or rudder when you cleat it on the boat.
When backing in I would then grab both of the lines at the same time, Drop the spring over the midship cleat and then walk forward with the the other line and drop it over the bow cleat. Use different colored lines so you can easily figure the difference between the two.
Last edited by chef2sail; 05-28-2011 at 08:51 PM.