Get the heaviest danforth anchor you can lift, you will need to deploy it in an emergency so no good if it's too big but equally useless if too small, make sure it's got at least 6ft of heavy chain, don't count that in the weight, it will follow the anchor overboard on it's own!
I also have mine on the back next to me with the rope tied to the front of out narrowboat with the rope stored neatly so it won't catch on anything when on the Trent, i want it in the water pronto if the shit hits the fan