Apparent Wind Sailing – Escape from Hull Speed
Sailboat performance has changed beyond recognition in a few short decades. The performance envelopes in Figs 1 to 5, below, indicate just how great the first part of this change has been.

From the days of the Roman galleys, with their little ‘downwind-only’ sails, to the Middle Ages and the ‘upwind and downwind-capable’ dhows, with their fore and aft rigs, to the globe-circling clipper ships and on through recreational sailboats until about the 1930s, all well-shaped boats sailed relatively easily up to the speed of a wave of their own length – this is called hull speed.  

But they always have been, and most sailboats still are, baulked from all higher speeds because as soon as a boat exceeds its hull speed, its stern sinks into the trough of the wave of its own making. In this situation it becomes a heavy body that is being pushed ‘uphill’, the drag increases rapidly and to sail faster needs much more power than sails can normally provide.  

Until the 1930s all sailboats were either too heavy and/or their sails were not big enough to push them over this hump in their drag curves.......

See Seahorse March 2001 for this article in full