The drag of a dingy goes up a LOT when it turns over! It's a good test of your painter.
Our club runs races where some of the boats tow a dingy. They're given a 12 sec per mile handicap. No feeling for whether that's too much or too little.
I always tow without the engine. I've tried adjusting the length of the painter so the dingy is riding on the front of the second stern wave. That seems to help, but as boat speed varies, so does the needed length of painter. I'll often tow the dingy close, with the painter led over the stern rail. This gets the bow up and tends to lift some of the dingy out of the water.
Offshore or overnight, I like to put the dingy on deck but it's really too big for the foredeck. 11' dingy on a 30' boat is a bit much - I need a smaller dingy or a bigger boat..