ok this singing thing- what you are doing is occuping your anxious mind.This nervous,critical and very active thing
sees the guy behind catching up or going faster or higher and makes you tighten your grip on the tiller grit your teeth and look for faults or things to blame. It actually interferes with you sailing the boat!Keep it occupied (in this case by singing!)
Your subconcious mind which helps you do everyday things like walking,eating,driving etc just fine without overanylising them is then free to sail as if on autopilot.
You find alterations to sails and trim are much more fluid and automatic.
You cant force this feeling but can learn to allow it to happen.
Make sense ?
Good book on this is 'The Winning Mind'.

gary