An integrally formed fibreglass fin assembly (1) including a base (2)--that is defined by broken lines (3,4)--for mounting the assembly to an object in the form of a surfboard (5). A primary fin (6) extends upwardly from base (2)--in that it extends upwardly from line (3)--and has a compound arcuate leading primary edge (7) and a compound arcuate trailing primary edge (8). A secondary fin (9) extends rearwardly and upwardly from base (2)--in that it extends from line (4)--and has a compound arcuate leading secondary edge (10) and a compound arcuate trailing secondary edge (11).