Regarding the migrating CE problem, why not design cat hulls with two sets of CB trunks rather than one "comprimise" position - shift the boards when spi is up, no need for oversized rudders, less drag? If you didn't want two sets of CB's you could use "rubber slats" to automatically seal the bottom of the unused CB trunks to keep flow non-turbulent there as they do on retractable CB windsurf boards.
