Reported by Martina & Reinhard Model:
Following information which might be interesting to other sailors (October 2017):

Our yacht flies the Malaysian flag, my wife and crew, as well as myself, are Austrian citizens, we both have one-year non-O visas for Thailand.

Coming from Terengganu, Malaysia, we cleared in at Koh Samui (my wife as a passenger). In Koh Samui, I tried to get information about the requirements for departing to Europe by plane whilst leaving the yacht in Thailand. Immigration on Koh Samui was unable to give me any information and told me to ask at Customs. Customs explained several times (including the boss of the desk-officer), that there is no requirement. They said, “Just take your luggage and travel home“.

After arriving in Koh Chang, we contacted the Laem Ngop Immigration office. Here we were told about the correct procedure which is as follows:
– Bring ALL required documents to the Immigration office – in paper-copy (Passport, contract with marina, plane ticket incl. return-flight).
– Pay a deposit of THB 20.000 which will be refunded on your return to Thailand back at the Immigration office.
– I received an envelope which I had to hand over to the Immigration officer at the airport on departure.

Everything was clear, smooth and without any needs of discussion.