>>105581211. Barbarossa was an old man who probably died from a stroke.
2. Plate armour was not even invented during Barbarossa's lifetime.
3. The fact that you can't swim in heavy armour does not mean that it's impractical to be worn on battlefields which usually aren't located underwater.
4. During the golden age of infantry-based sea battles, i.e. the 16th century, Europeans armoured themselves in plate with great success, e.g. during the Battle of Lepanto. Apparently they regarded the risk to be stabbed or shot greater than the risk of drowning.