I was staying in Hanoi and wanted to head to Cat Ba Island, but didn't want to sign-up for one of the 3 day Halong Bay cruises due to the lack of flexibility. So, I searched for how to reach Cat Ba Island on my own, but found a great deal of wrong/conflicting information.
I successfully arrived in Cat Ba Island 6 hours ago and thought I'd share my method.
Trip takes about 5 hours and costs $15USD (February 2014).
1. Train from Hanoi to Haiphong
Hanoi Main Station (Early Morning)
A 3km south of Old Quarter. Suggest getting a Mai Linh Taxi
HP1: Departs 6:00AM / Arrives 8:15AM
Hanoi Long Bien Station (Late Morning)
Far north side of the Old Quarter tucked inside an alleyway market. A bit hard to find. So, go there early and don't be afraid to ask the locals.
LP3: Departs 9:20AM / Arrives 12:00PM
You can buy the tickets on the same day at the station (70,000 dong/$3.50 USD). The train is a "tourist train" and slightly cleaner/nicer than the other trains.
2. Taxi to Ben Binh Harbor
Choose a Mai Linh Taxi. It cost me 34,000 dong ($1.60 USD) and took around 10 minutes to get to the harbor. There are two harbors! So, make sure you go to Ben Binh Harbor!
3. Hydrofoil Boat to Cat Ba Island North Port
Do not buy tickets from the ladies that will approach you when get out of your taxi! Go to the Hadeco ticket counter to buy your tickets. It will cost 200,000 dong ($10 USD), which includes the hydrofoil boat and a bus to take you to Cat Ba Town once you land. 45 minute for the boat and 30 minutes on the bus.
Hadeco Hydrofoil Boat Schedule
7AM, 8AM, 10AM, 1PM, 3PM, 4PM
I took the 9:20AM train and caught the hydrofoil at 1PM, arriving at my hotel around 2:15PM.
Tours on Cat Ba Island (Prices):
One Day - Ha Long Bay + Lan Ha Bay with lunch, kayaking, snorkling, & caves - $20-25 USD/PAX
Two Day/One Night - Ha Long + Lan Ha Bay + Dau Be Island with overnight boat stay, kayaking, snorkling, caves, and food - $55-65 USD/PAX
Two Day/One Night - Same as above but overnight in Viet Hai Village Bungalow - $60-75 USD/PAX
Hotel Prices in February were ~$20/night at a nice hotel.
Cat Ba Island also has a National Park with mountains/caves that can be trekked. 10km north of Cat Ba town and can be reached by motorbike ($5 USD/day rental).
Hope that helps some people!