(N1EE) asked:
What makes a boat weatherly?
What is the best keel type, hull form, and rig type?
What can you do to improve weatherliness on an existing boat?
Back your answer with an explanation.

Generically speaking, assuming we're talking about existing production
boats and not esoteric drawing-board possibilites, I'd answer:

Dictionary def: Ability to sail close to the wind with little drift to
leeward.

Deep fin. Low wetted surface; low CsubP. Masthead sloop.

Depends on the boat; but... Always helps to: change to fresh sails;
use appropriate sails for conditions; trim properly. If it has a full
keel, high D/L ratio, low aspect ratio, multiple masts, or similar, ya
just hafta sell it and buy something else.

Physics.