Depends what you want in a boat.
There are two things of many that define a blue water boat accepted by marine architects, one being the vessel has an up swung bow for reserve buoyancy on heavy seas and another being small ports to withstand crashing waves. On this alone you could remove many boats from the list that others would swear were blue water. If you want a boat that can safely withstand a tropical storm, then a Hirsh/Gulfstar 45 will work. It has sturdy rigging, full hull spider and well tabbed in bulkheads. It's heavy, (28,000 lbs) just what you want for open sea travel. And it is fairly fast under sail,(7-8knts). The real question is not if it's a blue water boat, (because most answers are opinion),it's are you a blue water sailor. A good sailor can take most anyboat anywhere. I have been in 50+ kt winds without damage in the Old Bahama Channel. I will post some pictures on my picture site here. The waves are big and ugly. For a size comparison, there is one where we are passed by The Majesty of the seas cruise ship and it is ugly out.