My main does not have a shelf .... and I'm fairly sure that most of the very
expensive laminated sails do not have one.

I'll bet they do. I think most people on here are confusing any main that's
attached to the boom with cloth as having a shelf foot. Most mains just roll
down and into the boom. A shelf foot is an extra cost option that allows the
main to maintain it's airfoil shape all the way down to a point parallel to the
boom. The main is attached to the boom with a foot made of inexpensive soft
Dacron that extends horizontally out from the boom (when the outhaul is eased)
to meet the main forming a flat shelf hence the name shelf foot. When the
outhaul is on hard the shelf foot disapears folding up on itself. It basically
has all the advantages of a loose foot but keeps the sail attached to the boom
along it's entire length. A loose foot may give the sail a very little bit of
extra sail area. Most laminated sails have either a shelf foot or a loose foot
only because of the person buying that type of sail is looking for a little
extra performance. A laminated mylar sail will still use a Dacron shelf.
S/V Express 30 "Ringmaster"
Trains are a winter sport