This is the passenger boat on the estuary of the Acheron River that takes you to Hades, the Underworld, where Ancient Greeks believed that the souls of the dead went.
Naturally Chris de Burgh's song came to mind
Chris De Burgh - Don't Pay The Ferryman
https://www.youtube.com …_channel=ChrisDeBurghVEVO
And there's the boat on the river
And when the rain came down
He heard a wild dog howl
There were voices in the night, ("Don't do it")
Voices out of sight, ("Don't do it")
Too many men have failed before
"Whatever you do
Don't pay the ferryman
Don't even fix a price
Don't pay the ferryman
Until he gets you to the other side"
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The ferryman should be paid after the journey or else the Soul would not reach Hades and would wander as a ghost around the places of the living.