attached is a screendump from XFLR5 showing a run with 1.5mill Re, Ncrit 3 on NACA0008 and NACA6308. You can see that the assymetric 6308 do provide better lift, but there are lots of tradeoffs in practical terms when it comes to assymetric daggers.
My Marstrøm Tornado rudders have some concavity between max thickness and trailing edge. I dont know what section it is, but I suspect it is a laminar one. Works good I would say, but sensitive to surface finish.
Differences between daggerboards and rudderboards are mainly that you dont want the rudder to stall as early as a daggerboard can. Rudders also operate in the flow behind the daggerboard/hull, so the flow is probably a bit disturbed. Even worse if you use assymetric daggerboards so the turbulence from the daggerboards hit the rudders directly, instead of being 3-4deg off as with symmetric daggerboards.
