The F18 in question does not have the wingmast so the tensions should probably be a little less than the Cap. I run about 400lbs of tension (using the same guage...sorry I don't know the number...My thought process for that is in lbs) and go up from there when we need to start depowering stuff and am experimenting with less on mine (I have a 2004 Nacra F18 with a mast that is probably a little softer than yours). If I remember correctly, my spreader rake is at 1.5".

I used to run a lot more tension because I was warned that the mast might invert...but I'm running with less now and finding better speed in the light stuff.