In all but light air, we sheet the spinnaker via an “outgrabber”.  This is a nearly forgotten technique from the heyday of symmetrical spinnakers.  It stabilizes the spinnaker when running deeply without having the leech get too tight the way it does if you just moved the spinnaker lead forward on the rail.  For racing it is specifically allowed by 50.3 (b) in the Racing Rules of Sailing.

For details see:

http://www.spinnakershop.com/Out-grabber.htm