I can’t understand comments like the above. Effectively, a boat is a boat is a boat, etc.? It’s nonsense. Take the example of the full-keel boat where the rudder and screw are well protected being incorporated into the design of the keel, versus the fin keel and separate spade-rudder design. Or, a skeg-hung rudder versus one that is fully exposed on the end of the rudder post. Far at sea, on your own, the protected rudders are much less likely to be damaged if the boat collides with debris. Far less likely to snag some floating line, etc. Far less likely for the keel and rudder to be severely damaged with an accidental grounding.
Blue water means sailing the open sea, far from safe harbor; in remote areas. Now-a-days people think to set off the EPIRB, PLB, or SAT phone on becoming disabled or worse. Then, when those classic boats were built, that was much less of an option, if one at all. The boats promised to sail the blue waters w/o the skipper and crew having to think about “rescue.“ If you want to test the bluewater chops of you and your boat, leave your GPS, chartplotter, AIS, EPIRB, SAT phone, cell phone, even weather fax, etc., at home, and set out in your Catalina 27, MacGregor 26, or whatever, for the Horn. Call when you get back. You’re allowed HAM and/or SSB.
BTW: Most boats now and “then” are/were lost due to hard groundings. Clearly, if that was a principal risk sailing in the ‘70’s and early ‘8O’s, then you’d want a boat that could survive it and get underway again, etc.