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Last time I talked with the Lasch Conservation Lab crew, there were still ongoing studies as to whether contact fuzes (or, even electrical detonators) could have been used, instead of the lanyard fuzes.
Pulling a lanyard on a torpedo attached to the target -- but detached from the Hunley -- supposedly would have involved deploying line from an external spool -- and automatically pulling the lanyard tight when they reached "the end of the line".
Pulling a lanyard with the torpedo still on the spar would have required crew (presumably, Dixon) to pull the lanyard from inside the Hunley -- which would have required a hole drilled through the Hunley's hull or conning tower. I'm not sure how the de-concretion has progressed since I was last at the lab, but, AFAIK, no such hole has yet been found.
I suppose the crew, at some point, realized they were still attached to the torpedo and the target.