Here is a harbour item from the amazing 1st series of Triang Minic Ships, 1956-64. 

M857  sea sheet in used good condition. There’s some white paint spots on one fold a slight tear on an edge.

Otherwise it’s pretty good and over 60 years old.  Yes it is a lot like a shower curtain. This is 26 x 26inches  or just over 600mms square.   Library photo.  Ref Sea1