From Port Blair it takes around 3 hours to travel to Havelock by ferry (there are ferries which go via Neil island as well). There are lot of private companies running ferry everyday between the islands apart from the government run ferry. Also, the private ferries have different categories of ticket, one can purchase as per their suitability (ferry tickets may cost from Rs.1500 to Rs. 3000 per person depending on the cruise line and class of ticket. Though government ferries cost much less, but they are not luxurious however moderate enough).
Better to book your accommodation well before your arrival, as during weekends & peak season availability of rooms can be an issue.
People usually stay around Radhanagar beach in here, as that is the famous beach here. A lot of sports activity is available here, like snorkeling, scuba diving (can cost 4000 to 5000 per person), better to make such arrangement locally.
–> Travelling around in Havelock island is easy, you can rent a scooter, which is easily available and doesn’t cost much. And if you are staying by the beach, you can relax the entire day there.
Neil Island, Andaman:
On your way back to Port Blair keep another night stay at Neil island, as many people considers Neil to be more beautiful than #Havelock. So better to go there next. Honestly i haven’t been to Neil yet—hence cannot write a lot, however whatever I have heard, #Neil is worth a visit for a night or two at least.