There are many boats departing Airlie Beach which go around the Whitsunday Islands, but not many focus on scuba diving itineraries. The longest trip I could find was a 3-day/3-night liveaboard on the Anaconda III, which also factored in some short island-hopping walks to see the pristine Whitehaven Beach and Hill Inlet Walk.
Anaconda III ventured as far out as the Bait Reef, some 2-3 hours cruising away from the Whitsunday Islands. Some good diving to be had, then sit back and relax amongst the idyllic islands when anchoring up for the night.
Batfish
Epaulette Shark
Octopus