I have used an (elderly) stock Hobie 18 SX spinnaker on Hobie 18, Hobie 20 & A-cat including last weekend. Works pretty well with 12.5 foot pole. Does not want to run as high as a modern assymetric however.

Dacarls:
A-class USA 196, USA 21, H18, H16
"Nothing that's any good works by itself. You got to make the damn thing work"- Thomas Edison