Get the 13 ultimate
I want one for the V3i , but they only make the 10x12 sef V rated coil for this machine now, before you spend money on an after market coil for the F2 , maybe consider venturing into the Teknetics Greek series line , I use the 13 ultimate on the Euro Tek Pro , and the same coil on the Omega 8000 , you can interchange coils in the Greek series line, the other option is to up grade to a high end detector, if your looking for more depth, happy hunting Earl