Asking "What Breed should I get" is kind of like asking "What kind of boat should I get"
Answering " You should get a Medium Size boat because small boats are cramped and Big boats are expensive " is way more informative than "You should get a Catalina because I have a Catalina"...(or " My friend has a Catalina ").
Hardly. When someone asks around this forum: "What kind of sail boat should I get?", the first reply is usually along the lines of: "How are you planning to use it?" The OP here asks what good breeds of dog would do well on boats, but he does ask about size. To some, size evidently doesn't matter much and even if it did--the size of the dog may or may not have anything to do w/ how well it works out on the boat. Unless you're a live-a-board, the dog is going to be at home w/ you most of the time--not on the boat w/ you. So, you really need a "dual-purpose" dog. A home pet for the family, plus one that you can take w/ you on a week-long cruise, etc., w/o it stressing out plus being a pain to you otherwise. In my opinion, a smart one that can be trained to do what it is told to do, etc., cute face or not. Or, more romantically, one that is "bred for boating." Are there really any such breeds? Some might say if you want that then you need a Belgian barge dog--i.e., a shipperke. Personally, I prefer a cat-- a pet that you don't have to take ashore twice a day, and does little on a boat beyond finding a cozy place to nap. But in any event, different breeds are suitable for different functions. That's why we have dog "breeds" to begin with--e.g., hound dogs, sheep dogs, police dogs, retrievers, and etc.