We found this shade in our boat after we bought it. I don't know what it is or who sells it, but it is awesome! It lays over the boom, from the mast all the way to the aft shrouds. It splits at the aft end of the boom and is tied together at the shrouds. We secure it to the lifelines and the shrouds as necessary. It has 3 adjustable poles for rigidity, and even goes over the bimini.
We had it up a couple of weeks ago during some pretty good storms, and it hung in just great. The biggest problem was a couple of small puddles (about a quart each) in the shade.