Depends how much you want to see. Last year the fireworks were pretty spectacular from as far away as Calshot Spit. I'd have thought somewhere on the water out of the way around the Brambles (LW Portsmouth is 21.49 BST ) would be fine if you cant find anywhere to anchor off Cowes.
You'll probably see more than you would from land anyway.
Thats what everyone else does. Try the bay to the east of Cowes (cant remember its name, begins with a B.....?).
Be careful of the motorcruisers with a load of drunkards on boards. When the display finishes they usually up anchor and floor it at 30 knots causing mayhem. Last year 2 boats hit each other and another couple grounded off Hamble spit.
Display is at The Parade, Cowes N50:45:53 W1:17:57
Youll have to have (very) long legs to see it from Osborne Bay. To see it, from the water, you'd need to have the Parade open of Old Castle Point. ie West of a Transit between Stokes Bay and Old Castle Point
I had thought about dropping the hook somewhere in the middle of the Brambles (twin keel so no major grounding problems)(unless it's rough of course). It will be springs (mostly) so the ferries and anything big should keep clear.
never mind the night time display - haven't you guys been out there this weekend? Fabulous amounts of chaos on the go - and plenty of verbal fireworks. Saw at least two boats without masts on Saturday and heard at least two maydays.
Saw one boat coming into Shamrock Quay with its mast in two pieces.
Had a good sail back on Sunday - we were cruising (on Starboard) among one of the classes (looked like IRC Class 2) - they were a very pretty sight with their spinnakers up in the sunshine.
I did actually alter course to make life easier for one of them, and got a friendly wave in return. Now that's not something you see very often. (But it was a French boat :-()