I am in the process of replacing some of my lines (jib and main sheet) as well. Below you find a list of lines and their length. Your mainsheet might need to be different from what is listed there, depending on the blocks you are using on your cat.
Line Lengths for the Hobie 16
Location Line Size/Type Length Quantity
Aft Tramp Lacing Line 1/4" Halyard 15' 2 ea.
Center Tramp Lacing Line 1/4" Halyard 19' 1 ea.
Downhaul Line 3/16" Halyard 5' 1 ea.
Mainsheet Line 7/16" Spun Braid 44' 1 ea.
Jibsheet Line 5/16" Spun Braid 32' 1 ea.
Outhaul Line 3/16" Halyard 7'6" 1 ea.
Main Halyard Line - Comptip 1/4" Halyard 51' 1 ea.
Main Halyard Line - Non-Comptip 3/16" Halyard 27' 1 ea.
Jib Halyard Line 3/16" Halyard 20' 1 ea.
Trapeze Adjustment Line 1/4" Yacht 3'6" 4 ea.
Trapeze Shock Cord 1/4" Shock Cord with 2 Loops 7' 2 ea.
Main Batten Tie Down 1/12" Flag Halyard 1'5" 1 per batten
Jib Batten Tie Down 3/64" Flag Halyard 1'5" 1 per batten
Hawaiian System Shock Cord 3/8" Shock Cord with 2 Loops 6'6" 1 ea.
also check this web page...
http://www.cat44.com/hobie-16-technical-info.htm 
