Mooring rope protection
When the engine room "blow tubes" ie injecting high pressure steam through the tubes the after deck is normally covered in soot particles. In addition the ships after mooring ropes on the drums often suffer from either sulphur burns or in some extreme cases actually catch fire. This simple protective measure was seen protecting the mooring ropes. Simply, It is a half drum placed over the ropes. Another method of protecting the after ropes is to cover them with fire retardant canvas.
Source UK P&I