Keeping a towed dinghy from rushing the mother ship when running downwind is a problem easily solvable by rigging a small parachute drogue to automatically deploy behind the dinghy whenever the towline goes slack....as it does when the dinghy starts surfing.

I put a funnel on the painter. It is held by figure eights ahead and behind. When the painter is tight the spout points toward the big boat, when it slacks the funnel becomes a drogue and slows/turns the dinghy.