15m
1 fathom = 6 feet
One fathom is around six feet.
1 shackle = 15 fathoms = 90 feet A unit of length used for anchor chain on ships. Anchor chains for ships are made up of 15-fathom lengths of chain joined by detachable links. The joins are...
Allowing for rounding error, as a very rough estimate, I would suggest 1.