Hi Vett
What ship is in the photo? It looks like it could have a lot of information for us. The common name for these platforms are tops and sometimes fighting tops. In the case of the one you show it is called a sprit (not sprint) top. Interestingly the term crows nest did not come into use until the 19th century and based on there being a sprit mast, this ship (the original that is) would be no later than about 1720.
Allan