From Bangkok :
Take the buss from Ekkamai buss station to Trat (about 6 hours).
Here you take a Songtaew (taxi) to the Leamngob pier (30 min.)
Then take the boat to Koh Mak (45 min).
Boats leave for Koh Mak at :
slowboat ( 3 hours )
- On Tuesday and Saturday at about 10.00
When you leave early you can reach the island in a day.
Otherwise spent a night in Trat and enjoy the nightmarket.
For more information visit : Kohmakguide.com