Billed as the "home of 20,000 affordable, newly typeset, reprint editions in two collections; Timeless reading and Nautical subjects", this site has quite a collection of books, booklets and plans from times past. A lot of good information to be gleaned here:

The Shellbacks Library

  Nautical books, Booklet bound Boat Plans,
Handibooks, Data Sheets, and Plan Sheets.
 
Boat Building and Design   Small Craft   Sail Boats
Power Boats   Canoeing and Small Boat Voyaging
Boatcraft and Fitting Out   Cruising and Seamanship
Square Rig   Knots and Sailmaking    Model Boats
Maritime History   Tales from Before the Mast   Surfing
For Young People   The Sea   Fiction   Music   Fishing Gear