John Vigor wrote a book on seaworthy boats. Small cockpits with a high bridge to prevent water in the cockpit from going below helps. Companionway hatch boards that lock in place. As to beam a wide beam introduces form stability while a narrow beam boat uses ballast. Some boats with wide beam are almost as stable inverted as upright ..think twin hulls. The general ideal is that a narrow boat will roll faster before flooding. The capsize ratio is a measure but also there are much more accurate ways to measure a boat's righting ability. My boat has a capsize ratio of about 1.7. Many Catalinas are greater than two. In general a boat with a CR greater than two is thought less seaworthy and more of a coastal boat.
Geeze, don't tell that to any of the Mini 6.5, Open 9.5's, 40's, 50's, 60's, or 70's...
Many many problems with generalizations... Companionway hatch boards that lock in place are a must for any boat in bad weather, skinny or fat.