Thanks very much for the comments. I originally thought the shot was a wash because the sky was a very very bright white overcast that day. Luckily I liked the framing of a few shots such as this one and I tooled around with the curves a bit. A lot actually, essentially the effect is like the 'solarize' filter, except I pull the curve all the way up to the top (instead of 50%) and then fool around with its exact placement. So essentially I switched the white in the sky to be black, and the gray in the shot to be white. So the photoshop was:
convert to b&w, crazy curves, then levels to even things out and the usual sharpening.
To give you a better sense of what I saw when shooting, here's the same shot in a color version (which I disfavor). PS on this shot was: up the saturation to get something besides white out of the sky, levels, sharpen.
I've only had a handful of shots in which this idea works, but here's another example of a very very stormy sky working well with the technique (usually you'd just try to up the contrast, but that made things very grainy and required masking out the boat, water etc., while this technique made the sky more dramatic still while also adding to the water and boat).