On the hard boat we have all round R/W/R on brackets coming from the mast 1m apart for night/restricted visibility and Ball/Diamond/Ball for daylight work along with a rigid A flag 1200mm x 1000mm mounted and covered when not in use. The all round white can be switched independantly and used as an anchor light. On the Dan we use a stobe at night and small A flag for daytime.
On the last diving rib (coded cat 4)we just used a rigid A flag of about 600mm x 600mm on a pole and never got into any trouble. We also have to call in the coasties to tell them where/numbers/when starting and when finishing for every dive. We also have to call in the Port Control, ours is channel 12, with the same information.
Hard or Soft it's never BIG enough