Ha Mcgillicuddy
The recommended size of tabs is approx 1” per 1’ of boat so 18” x 2 sids = 36” or footer. Most guys with a 23 footer would go with either a 12x9, 12x12 or the M120 which is a 10’x12” with a down fin. The M120 are pre packaged “not a custom made tab” some times you can find them cheep on e- bay by just typing in Bennett tabs. If you go to Bennett’s web sight they have a chart for sizing them there. You can also buy the M120 at any good marine hardware retail store.
FellowShip
Just for the Grins