They sell motion sickness pills at all Circle K and other convenience stores.

You should take motion sickness pills at least 20 minutes before departure. They have a slight side effect - mild drowsiness.
Tips for combating seasickness on a boat:
1. Try to look at the horizon, distant islands, volcanoes, and other stable objects. Avoid looking at nearby objects that are shaking, such as a phone or a book. For example, staring at a phone or reading a book will cause seasickness much faster.
2. You can go to the upper deck where it's windier and smells less like fuel. The journey is much easier to endure there.
3. It's better to sit in the center of the boat or closer to the stern. If the boat is small, the bow of the boat pitches heavily on the waves and causes seasickness faster. Also, avoid the smell of gasoline from the engines, as it greatly contributes to seasickness.
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