In Japanese folklore, funayurei are the vengeful ghosts of people who have died at sea. They are often the ghosts of sailors who remain in this world searching for former shipmates with the intention of dragging them into the ocean. Funayurei appear as dead bodies wearing white funeral robes. They are seen at night during new or full moons or on stormy or foggy nights. 

Takehara Shunsen
Funayurei appear as an eerie, glowing mist that forms into a ship with a ghostly crew as it approaches you. These ghost ships can charge into other boats causing them to capsize. They may also pull up beside a ship at which point the ghostly crew will try to drag it down under the water. Funayurei carry buckets and ladles and use them to fill ships with sea water in an attempt to sink them. 

Utagawa Kuniyoshi
In order to protect yourself from funayurei, carry buckets with holes to give to the ghosts to stop them sinking your ships. To avoid these ghostly ships, boats should sail directly through the glowing mist rather than turning. One last strategy is to throw food overboard as an offering for the hungry ghosts in the hope that you will distract them long enough to get away. 

Kawanabe Kyosai

Sometimes enormous funayurei appear alone and are often confused with another yokai known as umi bozu. Read more about umi bozu hereSome sources also depict funayurei as mysterious flames as shown in the image below.

From Tosa Bakemono Ehon

Mizuki Shigeru

Sekien Toriyama