I am just starting out. I have a 12 ft. Hobie ATR SUP (single fin) and the SLINGWING. I found it impossible to go upwind. Would it be helpful to use a larger windsurf fin to go upwind?

After a number of sessions I have been able to sail upwind with my Naish 4 meter wing on an 11'3" surfboard-style SUP board, with a single fin.  Mostly I have been winging in 6 to 12 mph. I've been taking a paddle with me to get back upwind to my small beach - at first necessary, and now for insurance for drifting downwind. SUP boards drift downwind quickly, so you need to stay on top of it. The higher wind in this range is easier as it keeps drive in the wing.  I haven't gone yet in higher wind, need to build more confidence I can sail home.

1) Fin size may help, I did put a larger fin on, but still could not stay upwind.

2) I also added a (temporary) center fin, and that helped, but not really enough.  I got one of these, cut some slots in the base and attached it to the board with some straps.  Dorky for sure.  Or you could glue it on.

3) Getting the wing in the right position helped the most, and I was able to finally point upwind. More so with the center fin, but also without it.  This video was the key for me: 

https://youtu.be/u5aZKfQFBNs