a torpedo then was a mine (some of them mounted on a rather long stick)
Here is a brief look at mine sweeping in the civil war...look under the "devils" the man who invented the Monitor invented one of the first mine sweeping devices...
http://books.google.com/books?id=SdrYv7S60fgC&pg=PA595&lpg=PA595&dq=American+civil+war+minesweepers&source=bl&ots=lYTAxPPxOz&sig=DGlWrzmDiiCaIoDLyOOFQgPDfII&hl=en&ei=cDisTdq_IYvVgAfB54z0BQ&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CBcQ6AEwAA#v=onepage&q=American civil war minesweepers&f=false
Here is little about Mobile Bay mine clearing operation... It seem they used wooden boats...
http://books.google.com/books?id=lmWLppXvSVoC&pg=PA317&dq=mine+sweeping+Mobile+bay&hl=en&ei=-zusTf3_OaTf0QHO7vHWAQ&sa=X&oi=book_result&ct=result&resnum=5&ved=0CEAQ6AEwBA#v=onepage&q=mine sweeping Mobile bay&f=false
I am finding ships sunk in the Civil war doing minesweeping duties...like the USS Rodolph
Assuming the role of a minesweeper and getting sunk
Diverse and dangerous duties in Mobile Bay and in nearby streams kept the "tinclad" busy until almost the end of the Civil War. The most difficult task facing her and her sister ships was clearing torpedoes (mines) from the captured Confederate waters. On 1 April 1865, as she was towing a barge to assist in salvaging the sunken monitor Milwaukee, Rodolph was herself sunk when she struck a mine in the Blakely River. The explosion killed four men and wounded 11 others.
Here is another ship sunk minesweeping....USS Sciota
Sunk while clearing mines
In November, Sciota was ordered to Pensacola, Florida for repairs. In January 1865, she steamed to Mobile Bay to help clear torpedoes from the waters there. On 14 April, the day of President Abraham Lincoln's assassination, she struck a torpedo and sank off Mobile, Alabama. Her commanding officer, Acting Lieutenant James W. Magune, reported:
"The explosion was terrible, breaking the beams of the spar deck, tearing open the waterways, ripping off starboard forechannels, and breaking fore-topmast."
It seems Mine sweeping operation in the Civil War has been overlooked by Historians.....I just did not find much on the topic...