A quick post holiday update for info....
I eventually chartered a Catalina 350 from Charter Yachts Australia in August. (
www.cya.com.au)
Weather was good but the water was a still a bit cold (wetsuit required) but at least there were few jellyfish (stinger season starts Sept/Oct).
No problems at all with Boat or Charter company. However, if you are thinking of going, you need to be aware of all the 'extras' you will be charged at the end of the charter eg. diesel for the yacht, petrol for the tender, cooking gas, overnight marina charge if you overnight in the marina on your last night etc.
Charging for these extras seems to be normal practise when chartering in the Whitsundays but it added over $200 AUD to the final bill!
For anchorages and much, much more, the book called '100 Magic Miles of the Great Barrier Reef' by David Colfelt will provide everything you need (all charter boats have a copy)
Would I go again........definately
John