Thanks once again for your suggestions, and for the reasons mentioned above, I WILL add a length of chain to the Danforth.
This said, my worst case scenario assumes that I'm dead in the water
(holding for a drawbridge) when the engine
dies, and that only the current is carrying me forward, so I don't quite see how the 100-lb. anchor could "sail on its flukes", as opposed to dropping straight down. The way I see it, the only relative motion involved would be that of the current vs. the bottom when the anchor finally lands.
Unless I also install a boom winch
of some sort, retrieving that much anchor and chain after the fact is definitely going to be a problem, but I'm not above eventually cutting it loose if it can save my boat
and a bridge...
The good part is that I might get lucky enough to be able to use my bow and stern thrusters to push her out of harms way and beach her before it comes to that, but I like the idea of having a Plan B just in case.