Austin Murray

The boat doesn't just disappear after long distances but the chance is greater. If there is another player in the world they are still able to see the boat and use it. When they use it they freeze standing above the water and will teleport to wherever they get out. It may or may not disappear for them. If they break the boat it will reappear for you once it is place again. 

Its not just after long travel. Most of the time when exiting the boat it will disappear. If you have another person playing with you they are still able to see the boat and use it and it's not until they break it that it reappears.  If they use the boat while you are unable to see it they will freeze standing above the water and when they exit the boat they will teleport to where they got out. The boat will still be invisible and turns invisible for them too.