Packing Size:
1/4" x 1/4", two rings, or
3/16" x 3/16", three rings

Highly Recommend: Gore GFO packing

Here is one place to purchase
http://www.emarineinc.com/categories/Packing%252dShaft/

Here is an EXCELLENT article (by a former C36 owner) with all the details, drawings, photos, etc.
http://www.pbase.com/mainecruising/stuffing_box