You need a bridle. Can be made up by anyone competent at rope work (not me).
1 carrabeena (is that how its spelt) on each side of the engine cliped to the towing eyes and a piece of rope between them.
The ski rope is then attached to a roller on that rope with a float on it and that roller allows the ski rope to go from one side of the engine to the other as the skier cuts across. Putting a float on it is pretty important tho or it tends to get stuck in the prop
mine was made up for me in a chandlers but you can buy them ready made for about a tenner.