Lots of people have taken inadequate boats offshore and survived, but that is not recommended. If you really run into bad weather and seas, that is where the inadequacy surfaces. How a boat is constructed is the main criteria for adequacy and above. Furthermore, if you are doing some passage making, it makes sense to have a boat with adequate fuel and water supply as well for comfortable cruising. There is a classification of boat quality and what they can withstand and it goes like this:
Category A - Ocean - Designed for extended voyages where conditions may exceed wind force 8 (Beaufort scale) and significant wave heights of 4 m and above but excluding abnormal conditions, and vessels largely self-sufficient.
Category B Offshore - Designed for offshore voyages where conditions up to and including wind force 8 and significant wave heights up to and including 4m maybe be experienced.
Category C - Inshore - Designed for voyages in coastal waters, large bays, estuaries, lakes and rivers, where conditions up to and including wind force 6 and significant wave heights up to and including 2m may be experienced.
Category D - Sheltered Waters - Designed for voyages on shelter coastal waters, small bays, small lakes, river and canals when conditions up to and including wind force 4 and significant wave heights up to and including 0.3 m may be experienced, with occasional waves of 0.5m maximum height, for example from passing vessels.
What this all breaks down to is how the boat is built, i.e. hull to deck joints, keel attachments, hull construction, proper spars and sails, window size and thickness, companionway drop boards thickness, bridge deck height, scupper sizes, engine sizes, deck hardware to include winches, railings, lifelines, & associated material, on and on and on. Size isn't as important as strength and how well found a boat is. Jerry Speiss sailed the Pacific on a 10-footer. Not the most comfortable ride, but the boat was built to withstand the conditions and he was an explorer writing about his adventures (not what mos of the rest of us would do). Lyle Hess designed strong boats that were 17 and 20 feet and up which were considered to be built for more extreme conditions. And Everette Pearson, who introduced the Pearson Triton 28 (a Carl Alberg design) as one of the first affordable fiberglass cruising vessels which skyrocketed others to build similar products. Everette Pearson just died over the holidays, by the way. I have met the man and he was special. Anyway, that's my 2 cents.
