Are vertically resting shipwrecks unique?

Is a shipwreck resting vertically a unique occurrence?

No. Several vertical wrecks are known in the Great Lakes and Baltic, although the exchange does not confidently identify a particular one.

Several known wrecks rest vertically, including examples in the Great Lakes and Baltic. For a Great Lakes case, accumulating ice may have added weight as the vessel descended while preserving its upright attitude. The exact wreck is not identified confidently from memory, so the useful takeaway is the general phenomenon rather than a specific attribution.