I've been fishing every day I get from 4-7 Asos a day.  once I got about 25-30 I fished up the nets. I did about 30 nets a weekend for about 3 weeks.  I also wore about 1900 Luck, I dunno if that really helps or not.  but I did get the Anchor After my Luck Statue ran out.. so I was at about 1700 luck when I finally got the anchor.  though I was only pulling 2-3 Artifacts a weekend.  the strangest part was.. the weekend I did pull it.. I got in order.... Lolo's Lute, Gwens Harp, Nox's Bow, Ghost Anchor... I pulled 3 luna white artifacts within 2 hours.