60 ft seems to be the standard towable tow rope length. I haven't looked to hard but i don't think I have ever seen one any longer. A standard ski rope is 75 ft. A ski rope will sometimes have sections that allow it to be shortened. As far as keeping tubes in the middle good luck. After a good whip if the riders aren't heavy enough to create some momentum to come back inside the wake the tube will just hang out outside the wake until you whip it the other way.