From an engineering/design perspective, the boat characteristic that allows good windward performance is LOW DRAG.
DRAG is produced both in the air and in the water
. Drag in either is seperated into 3 types for design purposes.
1) Form drag, caused by just pullin the hull/rig through the water/air.
2) Induced drag, a side effect from generating lift
(forward force on the sails
, lateral resistance from the keel
3) friction drag
Form drag is reduced by having the smallest possible hull
in the water
and the least windage above the waterline.
Induced drag is reduced by having high aspect ratio rig and keel
Friction drag is reduced by having a smooth bottom.
Anything that you can do to reduce drag will improve windward performance. Anything that adds drag will reduce windward performance.