We have been searching for info about this and are coming up empty handed. We would like to go to Halong Bay, and specifically would like to spend longer at the summit of Titop island and be there when the tour groups are not. Is it possible to charter a longtail-type boat (or the local equivalent) to just take us there in the afternoon and bring us back after sunset? Even the higher priced tours seem to stick to a rigid schedule and (not that we've found any) private boats are most likely prohibitively expensive. We are coming to the end of our 7 month travels, so money is tight, but a little splurge on a credit card could also be rewarding.
Thanks for your reply. We have checked with some tour operators, but it seems that if you are joining a tour you must stick a schedule (obviously. You need to accomodate all the passengers, not just the two picky ones!) and if we want a private junk it will $400-500. We are wondering if there are smaller boats that can just take us out for 4-6 hours (probably from Cat Ba town as it seems to be about 25km from Titov).
I can now answer my own question, in case anyone else is wondering.
We ended up taking the bus to Cat Ba with Hoang Long from Luong Yen bus station in Hanoi. 180 000 dong got us right to the strip in Cat Ba town (bus to Haiphong, bus to port, ferry to island, bus to town, the fact it all worked out with no waiting was impressive).
We looked at a few rooms and picked a clean double (2 double beds actually) room with AC, 4th fl balcony looking out at the bay, hot water, mini fridge for $8 a night.
Our hotel booked us a boat tour, private, 4 hours to wherever we wanted to go, followed by motorbikes to the Hospital cave and a drop off at cannon fort for sunset. All for $60 for 2 people. More than a group day tour I know, but we had control of the itinerary. There are also good kayaking trips into Lan Ha Bay (according to the friendly travellers we met hanging out in cat ba).
We are glad we spent a couple days in the town and saved the money. We have spent time sailing though, so for us there is no novelty to sleeping on the water. The scenery is breathtaking, definitely worth a trip.