Look at that fine model above. The blast from that large of a charge, underwater, that close to those brave men, must have taken them out. Did the designers test the idea of underwater detonation survivability before they sent the Hunley out?
In which direction was the Hunley pointed when they found her remains? If they were able to turn her around, then the blast could not have killed them instantly ... ? Or, if pointed home, could she have drifted a while and turned herself around before settling? That the crew was still sitting at their stations and the commander's watch stopped at the moment of impact is the most telling evidence. God those men were brave ...