In the age of sailing warships a century ago, the shipbuilding craftsmen of each City-State followed one rule when working on the keel—they had to cut a piece of timber from the raw wood material.
They would treat this piece of wood in the same way as the keel, through carbonization, steeping in medicine, and oiling, and they would place it together with the unfinished ship on the shipyard. However, once the ship was completed, this piece of "Keel Timber" would be left in the shipyard and permanently preserved on land—usually, the ship owners would also pay extra money to have the priests of the City-State regularly bless the timber, or they would simply send it to the church for safekeeping and supervision.
At first, the practice of preserving the "keel sample" was part of a quality standard for ship owners to verify the selection and initial processing of the keel to meet the technical requirements of a ship. But later, it became a symbol of praying for safety—