  L248/81-- RUNNING ON THE 540 METER ARC WITH DRAG, LAUNCH 519 SNAGGED ON THREE OCCASSIONS.  DIVE TEAM WAS DEPLOYED AND INVESTIGATION REVEALED SNAG TO BE A 25 FT SAILBOAT LYING KEEL UP IN 22 FT WATER LWD.  A LEAST DEPTH WAS OBTAINED WITH A LEAD LINE BY D