my blowers are now overdriven, so i have to use 92, we have 92 on our lake so it's not a problem for me.

not sure additives, if you research them, are a viable option for a boat. you'd have to add gallons of it just to raise the octane a couple of points.

before overdriving the blowers, i did, on occasion mix some 89 with my 92 (just got 92 on the lake in the past two years). never had any problems with that, but i was only at 4lbs of boost.