Kapal Feri ke Anambas
If you prefer taking a ferry to Anambas, as opposed to taking a flight, then make your way to Batam or Bintan, both south of Singapore. From the ferry terminal in Singapore, you can take a ferry to Batam or Bintan - it's about an hour's sail for either.
After you've arrived in Batam, go through passport control and customs and then head for the ferry terminal for Anambas.
The Batam ferry to Anambas doesn't leave as early as the Bintan ferry to Anambas, but it's a good idea to make a bee-line for the ferry terminal all the same, as there isn't a lot of leeway, given the arrival time of the ferry from Singapore.
If you find you're cutting it fine, due to a ferry delay or traffic jam, or some such, contact your ferry ticket provider. They may be able to assist you.
For more information on the Batam ferry to Anambas, click here.
Alernatively, you take the Bintan ferry to Anambas.
Once you're in Bintan, head for the ferry terminal there. In all likelihood, you'll need to arrive the day before, as the Bintan ferry to Anambas departs quite early, given that this ferry takes a couple of hours longer than the Batam ferry to Anambas, i.e. about 10 hours or more for the Bintan ferry versus about 7 hours for the Batam ferry.
By the way, both the Bintan ferry to Anambas and the Bintan ferry to Anambas stop at Letung first, which is in Jemaja, before making their final hop to Tarempa, on Siantan Island.
In addition to the Batam and Bintan ferry to Anambas, there's the Bukit Raya, a passenger cruise ship, capable of carrying close to 1000 passengers between Bintan and Anambas.
That being said, keep in mind that the Bukit Raya only services this route about twice a month. Also, the Bukit Raya isn't nearly as fast as the ferries above, which means that it can take up to 20 hours to reach your destination. Lastly, this cruise ship doesn't really have a schedule as such, so it's a lot harder to book in advance.