I will have to try that design. A good design I use for crappies is a size 12 yellow bugger with black hackle and or white dry fly hackle.I would not let it sit on top but would twitch it sub surface.
Were you letting that sink and twitching it,or where you letting it float?
Cause the crappies I fish don't realy take anything on top water, but with take a sub surface.