I have seen "ally" skinned plates and rudders for a serious contender for Cherub skiff class....

They had a backbone stringer made of wood and the plate ally was folded. The backbone then formed the max depth. The issue is sealing the trailing edge and keeping the plate ends at the trailing edge together. They solves it by riveting the two edges and silicon sealing. It worked.. At that stage one couldnt weld easily thin plate end to plate end. The other issue is the temp to weld would warp the plate near to the trailing edge and thus create uneven flow.. High speed and uneaven flow isnt much fun..
I dont think much was gained over a conventional plate.