Thanks for your reply, I would like to carry the spare in the rope locker, obviously I will have to add some more chain. There will be all sorts of bottoms from beautiful sand to rock and coral.
Yes, I know my existing anchor is a little small
Brian, Hopcar was just yanking your chain, so pay him no mind, as they say.
I think your Rocna is quite heavy enough.
As to your query, I have been to the Whitsundays, but not personally cruised there bareboating, that is still on my bucket list. Our current boat has been up there with previous owners, but we just don't have that sort of time. My holiday would be spent just getting up there and back. But yes, I except the bottom would vary from sand through to coral, with some mud off river mouths only. Your Rocna would do fine for virtually all of that. The only one which might be a bit more versatile, especially over coral and rocks, would be our Aussie designed and made Super Sarca, (sand & rock combination anchor), with the tripping slot. However, I must admit bias, because I've got one. For my back-up, I have a large Danforth, with a mixed chain and rope rode, which has never seen the light of day out of the lazaret, so the advice re a Fortress or Danforth type second anchor is probably quite reasonable.
However, up there, something that won't damage coral, and can be retrieved easily if it snags in coral or rock could have the edge. I doubt you will encounter soft mud up in the Whitsundays. Seriously, I think your Rocna would be fine virtually everywhere, but set a trip-line with float if near rock or coral. Actually better still, where there is coral, I believe they like folk to use moorings placed there to save coral damage, so grab one of those if at all possible.