During the 16th and 17th centuries, naval battles were frequently brutal and resulted in a significant number of casualties. Given the limited medical knowledge and resources available at the time, many of the wounded sailors often succumbed to their injuries during long sea voyages. To handle the increased number of deceased individuals onboard, it became necessary to construct temporary coffins or biers for their bodies.
These makeshift coffins were often constructed from the wooden planks readily available on the ship. It was a grim reality that a sailor's body would be placed on two planks, with perhaps a third plank added to cover the body. The notion of “two planks and a passion” originated from these simple wooden biers used for the deceased at sea.
The “passion” part of the phrase carries religious undertones. It typically refers to the Christian belief in the afterlife, where the soul of the deceased person departs from the physical body to a higher plane of existence. The passion in this context alludes to the notion that one's soul transcends the physical realm after death.
Over time, the phrase “two planks and a passion” became a poignant expression in naval culture to acknowledge the sacrifice and loss of fellow sailors. Eventually, it began to be used more generally to refer to the burial of someone who has passed away. Although it originated in the context of sailors' burials at sea, the phrase “two planks and a passion” has come to represent the universal experience of mortality and loss.