[mrsmith]

Scientific article with math and numbers:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0182244

[Southack]

Article doesn’t say, but the killing zone of the blast radius of 135 pounds of packed black powder, underwater, would be roughly 10 meters in every direction.

Hunley was 5 meters away with the spar.