There are two conditions for sailing against the current:
The dragon sand is short, and the water needs to cross the tomb from the left, while the tiger sand is long and angular (with its own mountain), so that the tiger sand can meet the current and the water can be used as wealth.
Tiger sand is short and needs water to pass through the tomb from the right, while dragon sand is long and horn-shaped (with its own mountain), so that dragon sand can catch water against the current and make money from the water.