A87 has a boats length – 26′ of 1/4″ chain and 140′ of 1/2″ nylon warp (not that I have used it yet!!)
YNZ recommendations are:
A cable the boats length on deck of chain (minimum) plus 195′ of rope or chain plus a second anchor cable of 19′ 6″ (minimum) of chain plus 130′ of rope or chain.
For a yacht of the Atalanta’s size and weight 6mm chain and 10mm dia rope are adequate for use with a 7 Kg CQR or Bruce anchor or a 13S Danforth type anchor
Also depends on the areas you intend to anchor in and of course what type of anchor you use.