Indeed, it is rather puzzling. It's definitely a landowner's map, from his own archive; there's a scale of furlongs but the distances between the known points are way out, and the most significant building known to have existed here in the 18th century is entirely absent (it appears on a coastal survey of 1714). There was no other building development here until 1807.
The '1750' copy is very rough, and is on paper but without any discernable watermark. The writing on the back appears entirely unconnected with the map itself, being a note of rent collections but not from this district, which suggests to me that by 1750 it was being used as scrap paper. The ships are omitted, but the sections of coastline and estate boundary have compass directions marked; alternative lines for the boundary have been erased, leading me to suspect that if not a draft for the neat version, then it was perhaps a copy of the neat version and made in connection with an unidentified legal case - it has a label 'W1' characteristic of documents produced as evidence. The boundary remained in dispute until 1805.
Anyway, this lack of clarity in other evidence explains why I was hoping that the ship drawings might help!