The easiest way to reach Koh Nang Yuan is by a long-tail boat from Sairee Beach on Koh Tao. To rent a boat is incredibly cheap at only ฿ 150 each way, and if you schedule a time with the driver he will even come to pick you up. You can also reach Koh Nang Yuan by ferry, but this would only be for visitors that are staying on the island as the ferry doesn't come back to pick you up until the following day.