d.floating derrick: one erected on a kind of boat, with a horizontal boom supported by stays from the top of the central post.
ΚΠ
1874 E. H. KnightAmer. Mech. Dict. I. 688/1 Bishop's floating-derrick..used in 1850..is capable of self-propulsion by means of paddle-wheels, and thus removes its suspended load to a position of safety for repair or other purpose.