I used four equal sized small Al Merricks - it seemed slow on the first “push”. Small Als in front, big Als in back were nicer, it felt like I could pump it rail to rail better - but I switched to fiberglass fins before I got the full effect. I think there is potential to explore!
thanks for the replies guys [it took me ages to re-find this thread]
I have four fibreglass fins I made that are slightly larger than the fcs ‘GS/ GL’ template …[maybe ‘popeye’ can test pilot these one day this autumn / winter !]