DOTLAN EveMaps

Gibbet usually refers to a gallows-type structure from which the dead bodies of executed criminals were hung on public display

Pirates were sometimes executed by hanging on a gibbet erected close to the low-water mark by the sea or a tidal section of a river. Their bodies would be left dangling until they had been submerged by the tide three times.
Particularly notorious criminals' bodies could be hung in cages as a warning to other waterborne criminals of the possible consequences of their actions.