After a certain size, it's about design. Our family 56 footer was specifically designed to single-hand. She was shallow (5') with a 3/4 keel, narrow (12'), and built with three masts to keep them small enough that one sailor could hoist them alone, sail across an ocean with all three set, or maintain balance with the foresail and mizzen, or just the main set. She also had a big engine in a full sized engine room. Well, the engine room was beneath the center cockpit, so you did have to crouch a bit.
-Will