误He went to Changsha by the boat.
正He went to Changsha by boat.
正He went to Changsha on a boat.
正He went to Changsha in a boat.
析表示“坐船”用in a boat, on a boat或by boat均可。侧重交通方式时用by boat, boat前不加冠词。侧重具体的行为则可用介词on或in,须加冠词a或the。