If the scratch just scratches through the varnish, just re-varnish.

If it's down into the glass (broken fibers in the weave), sand away the surrounding varnish, re-epoxy the gash, sand it smooth, and re-varnish the area or the whole boat (whichever you have the time and inclination for!)

Shawn
: Having just finished glassing the outside of my Coho hull (which was an
: interesting experience and one I could not have done correctly without 1st
: time help - thanks George!), my thoughts have turned to eventual repairs:
: When the boat is done and varnished and I need to repair a deep scratch or
: worse do I need to get below the varnish layer(s) to re epoxy or not?