If your dog is trained, he will behave calmly in the boat. German Shepherds are great to train, so I think you won't have a problem. This breed of dog is very popular because they can do different tasks. I also have a German Shepherd and had Service Dog Registration to officially register it as a service dog. It is very convenient because the dog accompanies me everywhere and helps me to navigate in space. I have vision problems, so it's hard for me to get around without help.