There are three options how to get on to the Tidung Island by boat.
Speedboat is the fastest and probably most comfortable way how to get there.
Speed boat departs every day at 8am (scheduled time) from port of Ancol. This is the fastest (1.5Hrs) and most comfortable way to get to island. You are required to purchase the tickets (Rp. 150,000 weekends and 125,000 during week days) in nearby ticket office. You can bring up to 10Kg of luggage per person, in some cases if you are bringing large luggage they will charge you for extra weight (about Rp. 20,000 for each 5Kg extra). Please note that you need to pay Rp. 25,000 per person to enter Ancol Marina area.
Speed boat departs every day at 8:15am (scheduled time) from port of Kali Adem. This is the same boat that departs Ancol port, it just stops en-route to Tidung in port Kali Adem. You are required to purchase the tickets at the ticket office located at port's building at 110,000 per person.