Morty is our boat dog! Short legs for a low center of gravity and no tail to get caught in a winch!
He is a terrible swimmer, which is why we try so hard to keep him on board.
He always wears a life jacket to help him float while he would wait for his recovery, if he were to fall over.
To avoid a "Dog Overboard" situation, we keep him tied to the jacklines that run the length of the deck, allowing him to walk around. I also wove a net on the bottom half of the lifelines to help keep him on board.
The best way to keep him on the boat is to make sure that he is happy on the boat. Being how I raised him from a puppy on board Wisdom, this is his home and he doesn't try to escape (unless we leave without him, then he will jump off and chase after us).