Joe's explanation is the best.
There are structural/strength requirements and built-in 'redundancies' for a 'blue water' boat that make it 'safer' than a boat used for island hopping / coastal sailing.
A blue water designed boat is typically 3 (or more) times as 'strong' as it needs to be, while a 'coastal' boat will be typically only 2x as strong as it needs to be for the worst conditions. This '3 times as strong' is based on centuries of historical data ... those that are less strong typically dont make it 'on the average' for long passagemaking without repair or rebuild enroute, etc..
The features of 'blue water' boat will typically have:
• very strong and usually very small 'windows' or portlight to survive the rigors of the full weight of a boarding wave,
• a companionway that is really strong and can survive a large boarding wave that crashes over the stern.
• rapidly draining cockpit and usually a quite small cockpit so that if (or rather when) the boat becomes 'pooped' the small cockpit wont ship a LOT of water and will 'clear'/drain rapidly .... and small enough so that
you dont get 'washed around' in the cockpit. A large water filled cockpit can severely 'squat' the stern, making your stern lower in the water & even more vulnerable for the 'next' boarding wave.
• a large 'bridge deck' to prevent/lessen down-flooding from the cockpit to 'down below'
• Oversized or beefed-up rigging, chainplates, etc.
• A sail plan that can be easily reefed, and with 'multiple' reef points. Cutter rigs and Solent rigs seem to be the current 'favored' or preferred for long distance cruisers.
• Triple stitched and otherwise reinforced sails ... possibly will be set up with a separate mast track for a 'trysail'.
• A very strong hull, topsides, deck, coachroof and hull to deck joint.
• a boat that is 'SEA-KINDLY' - a boat with a gentle motion when in a large sea-state; not a lightweight 'vomit comet' whose fast 'roll period' will loosen dental fillings from your teeth .... a boat that wont tired you out after a few days sailing. More of a deeper v shape to the hull to prevent 'slamming' and 'pounding' as with the 'flattish' bottom as is found on the modern 'production type' boats.
• a boat that has
'stowage' capacity and wont sink deeply beyond the normal waterline when loaded; not a 'weekend' design.
• A boat that has adequate 'handholds' throughout the inside (and outside) the boat. This will prevent being 'slammed' against a hull side, etc. in a heavy seaway. Look for hand holds that are accessible so you
dont have to let go of one to reach the next .... all the way through the boat. Most of the modern 'production' boats seem to omit this vital attribute.
• Large capacity tankage - fuel & water.
• NO 'pullman berths', yet berths that can be rigged with leecloths - to keep you in one place when the weather is 'rough'
A blue water boat will be built to withstand just about whatever the weather gods may bring .... when you cant anchor for the night or run/scurry into a close-by 'port'.
For 'blue water' boats seek out those designers who specialize in such boats: Robert Perry, Bob Harris, Bill Creighlock, Rob Ladd, Peter Beeldsnijder, Petersen, etc. etc. and their boats: Baba, Tashiba, Oyster, Tayana, Valiant, Passport, Pacific Seacraft, Amel, Hallberg, Morris, etc. etc. etc. etc. .... all 'go anywhere' boats with 'proven' passage-making histories. Let these design characteristics influence your choice of the 'lesser' and less
seaworthy designs.
A 'coastal' boat can easily sail from Newfoundland, all the way down the East coast to Trinidad by 'island hopping' by waiting for the correct 'weather windows'. IF you want to go to Central or South America from Fla, etc (across the Lower Gulf, the Yucatan Channel, and the Western Caribb.) ... you really should have a 'blue water' boat, a 'sea-kindly' boat not a 'flat-bottomed cork' that is going to beat you up and thoroughly 'tire you out' when the weather turns 'ugly'.
