Yes it's perfectly doable as a day trip! Yes it is a long day and you will need transport! You could also spend a night there easily it's so beautiful and the Dhow cruise is not to be missed. There is full day or half day cruise.
You can do it as a long day trip from Dubai - if you don't have your own transport there are lots of tour companies who offer day trips that include a dhow cruise - some of them you can stay overnight on the dhow. If you have time and transport, it is really worth spending a couple of days up there to explore the mountains as well as the coast line - there are a few hotels in Khasab or you can camp if you have equipment.
If you want to do it as part of your Oman trip, it will take some time but could be a nice way to see the coast if you take the ferry there and maybe fly back to Muscat, or see if you can find some transport to take you back to Dubai by road (not sure if there is any bus service). It depends a bit on how much time you've got and what you like doing.
I can confirm that this is one of my favourite trips although it is easier for me as I live in Ras al Khaimah. Strange as it may be but this trip is in fact easier to do from Dubai than from Oman. Mussandam is an Omani enclave on the tip of the Arabian peninsular and is some distance from Oman. Easy enough to do under your own steam but this company organises tours from Dubai and is highly recommended http://www.khasabtours.com/
can you do this next week
-:- Message from TripAdvisor staff -:-
This topic has been closed to new posts due to inactivity. We hope you'll join the conversation by posting to an open topic or starting a new one.
To review the TripAdvisor Forums Posting Guidelines, please follow this link: http://www.tripadvisor.com/pages/forums_posting_guidelines.html
We remove posts that do not follow our posting guidelines, and we reserve the right to remove any post for any reason.