From experience, a dog you can pick up with ease with it's pfd handle, is an asset. Getting on an off a sailboat, especially from a dinghy is no simple task with some dogs. It is with a 13 pounder. On going long term, we find the smaller dogs more able to go on deck. It's simple geography I think. Their space they keep clean is smaller so the foredeck is like the back yard. Plus, it's not a big deal to clean up(dried dog food of course).

Leaving them below isn't as much of an issue(they can not get out, too little), they're just easier as a package to deal with. A 13 pound dog, even wet is not much to deal with. They have their faults! They bark at boats that go by....

Still, a big dog in good health isn't that much of a deal on a boat, especially if they can jump from dinghy to deck, and back(our springer did that with ease).

And I think dogs are like people. If you didn't take your kids sailing when they were babies, they might not like it later. Take them as puppies, they'll adapt nicely.