I'm not surprised. The challenge of "elastic" engine and drive-line mounts for steam rams was never solved. This was one of the more attractive features of the spar torpedo. Less shock to the hull of the attacking vessel and it avoided the risk of getting the ram stuck in the hull of the intended victim. This actually occured at least twice during the operations of Confederate ironclads. It does not seem to have happened during the attack on the blockaders by the Chicora and Palmetto State off Charleston. The first the the Virginia/Cumberland strike and the second occured during the river battle between the Albamarle and a converted ferry-boat that almost took the minimum buoyancy ironclad with her.