Boat can pass the Worldborder barrier at 29,999,999 blocks.

This appears to be a duplicate of MC-53444. If you feel that this issue is affecting you, feel free to vote for the duplicated ticket, to give Mojang a basic idea of how many people are impacted by the problem. Just to further inform you, this will not determine how quickly the bug gets handled or fixed. Like I said earlier, it just gives the team a general understanding.