Leonardo da Vinci designed a lifebuoy, a floating rescue device intended to help a person stay above water.
His design formed part of his studies of water safety and underwater activity. A buoyant ring could be thrown to someone in distress or used by a person entering the water. The circular form leaves an opening through which the user can place the body while the surrounding material supplies flotation.
A lifebuoy is different from a life jacket. A life jacket is worn, while a lifebuoy is normally thrown or held. Leonardo’s design is also distinct from a lifeboat, which supports several people and provides a small floating platform rather than a simple personal float.
The proposal reflects Leonardo’s habit of designing supporting equipment alongside larger machines. His underwater projects required ways to protect and recover people, not only ways to move through water. As with many notebook inventions, the surviving evidence documents a concept rather than regular historical manufacture.