I've recently taken ownership of 3470, Recidivist.
Just wondering is there is a ball park for rig tension people are running?
Also, T-Foils, are they worth it?
Congratulations on your new arrival!
We don't tend to measure rig tension, the general thinking seems to be the leeward shroud should be just swaying slightly upwind, not loose though. There are many more experienced and knowledgeable than me though, hopefully they'll see this post.
As for T-Foils, they work on the Feeling Foolish and Final Chapter, that is for sure. Given the Man - O - War is a modification of the Final Chapter, I'd expect it to make a substantial difference. Again, those more knowledgeable who have sailed more N12 designs than me, please comment !
There is a tuning guide on the website https://www.national12.org/hints/tuning_guide/ which gives you some excellent tips on rig set up. This is accessible to Association Members. Suggest you have a read of that and then post any queries here.
Regarding a T foil, it depends a bit on what you want to do, if you want to be a competitive as possible then it is probably worth it and need not be all that expensive. Graham Camm has written some very good stuff on the theory behind foils and how to make them. Several people will make and fit you a foil if you don't want to do it yourself. I had a foiling rudder fitted to a feeling foolish which Patrick Hamilton seems to be doing quite well with (I sold it to him when I decided I needed a boat I could sit in!). Dare Barry fitted a foiling rudder to the last Man O War he built I think so it maybe worth contacting him.