
Chances are you have never salvaged a vessel yourself or you have (hopefully) never seen a vessel upside down. But in case you have seen photos of a shipwreck or of a new ship getting launched from shipyard, you may have noticed that the bottom of a ship is most times red.
While many may have never really thought about this until reading this article, others, who do have noticed, may think that there is no apparent reason for a ship to be painted in an area which is always below the waterline...
https://safety4sea.com/cm-do-you-know-why-ships-are-red-on-bottom/