you can go from Ankarana to Nosy be in one day..its not te kms that are long but the road is quite bad for some of the way. You could stop in Ambilobe..very traditional town..a bit like the wild west, very colourful with so much life to see.
The road toAmbajana is also pretty with Cocoa plantations and ylang ylang...
Then you get to Ankify where you catch the boat toNosy be..beprepared to be hassled..lots. So do not expect to get straight on the bot even if they say it will gostaright away..it won't leave unless its really full OR you get a private boat..which actually is not a bad idea...
There is a lovely little bar where you can hang out and wait until the boat is ready..on the right hand side on the way to the harbour front.
Be sure to get there before lunchtime as the sea is terrible aftr that and sometimes the boats don't even go.
I prefer Nosy Komba to Nosy Be..much nicer beaches and nature and so much more Malagasy.
Enjoy your visit and try to take it slow rather than try to see everything..we have been there 4 times and still haven't seen it all....