only a plank between you and a watery grave; on a boat, you're just an inch from death
Proverb warning of the constant danger at sea; literally 'one plank below is hell'. Used to emphasize how fragile a boat is and how close sailors are to death.
The fisherman spoke of the terror of the sea, saying, 'Only a plank separates you from a watery grave.'
A traditional Japanese proverb. The exact origin is uncertain, but it reflects the perilous nature of seafaring life.