My wife and I had initially planned a Similan liveaboard trip, and had chosen the Danish-operated Adaman International Dive Centre (AIDC) because
1. the AIDC web site states that the dives take place in a marine park, thus promising good coral and fish life;
2. AIDC offered a 5d/5n trip with 19 dives, more than most other companies,for 24580 THB per diver including gear and park fee, translating into a good cost per dive ratio;
3. AIDC is operating out of Ranong, which is accessible more quickly than Phuket by land from Bangkok.
Due to a case of death that occured in the closest family, we had to cancel the Similan trip. Note that AIDC does not offer any refunds, not even under these circumstances. In order not to lose our downpayment, we had the option to join their later Burma trip at an additional cost of 7420 THB per person. The AIDC website describes this as “one of the most beautiful and unchartered places in the world”.

Arrival at the Dive Shop in Ranong
We were asked to meet at the dive centre at 12pm on the day of departure, the operator explicitly wrote to us not to be late. Our bus arrived at 11.20am, and the staff told us that the boat would leave late that day, although it was unclear at what time. We filled in the liability release forms. We were never asked to show our diver certification cards.
We then had to chose our rental dive gear. We would normally have taken M-sized wetsuits, but found that the ones in the dive shop were too small. We were explained that they were "Asian sizes". There was only one L-size wetsuit in the dive shop, which did not properly fit either, but was more comfortable than the too small M. All the wetsuits were ripped at the bum (we sewed one of the big holes ourselves).
We had to spend the afternoon waiting for departure. At no point were we told the time of departure. So we were having coffees until we were finally picked up and driven to the harbour at around 3.20pm.

The Vessel
AIDC operates the MV Thai Sea, which has 2 upper deck and 6 lower deck cabins accommodating 2 people each. All are the same price, despite considerable differences in comfort. We were assigned one of the lower deck cabins directly above the engine. The cabin stank of diesel fuel, and one could actually look at the engine through cm-wide slits in the wooden boards below our mattresses. The boat was full, so we could not change to another cabin. It was not possible for us to sleep in our assigned cabin due to the bad smell and noise. We would spend the nights outside, on the upper sun deck, but the maximum time of sleep we could catch was 5 hours per night due to winds, and waves splashing on the deck. During the day, unfortunately, there was no place to retreat to for the so much needed rest between dives. We were promised to have engines and generator shut down for the nights when the boat was anchored and not moving to the next dive site, but after the first night other customers complained about the heat without the generator-powered aircon, so the generator was never swiched off again at night. We were boldly told that we could rest after our return to Ranong.
Due to problems with the gear box, the vessel broke down twice during the trip: once on the first day, and once on the day return was scheduled for. Necessary repairs and towing resulted in the trip being 2 days longer than initially planned. Sadly, there was no offer of apology from the management for this delay.

Dive Personnel
There were two Divemasters (including the AIDC owner) and one PADI instructor as underwater guides. The instructor was assigned to lead us and two other divers. On our first dive, my wife found that she required an additional weight, so we resurfaced after seconds. The instructor did not check for us and left with the other two divers. We obtained another weight from the always helpful local crew and dived independently.
Further, it became clear during the trip that the dive personnel were not very knowledgeable about the dive sites or the marine life to be found. At one point, we were told the next dive was going to be a wall dive, but merely found a sandy bottom at around 8 to 12 meters depth.

Diving in the Mergui Archipelago
The Mergui archipelago is not a marine national park. Each night one could count on average 40 fishing vessels with bright lights, apparently Thai boats fishing in Myanmar waters. Not surprisingly then, there was barely any fish life on the reefs. Rarely a school of fish to be seen. We had to focus on nudibranches and cowries - and indeed we saw quite a few of them. During some of our dives, we also heard the sounds of close-by dynamite fishing, and we found most reefs in a deplorable state, being heavily damaged (broken and dead) by the devastating dynamite explosions. The only positive aspect was the lack of coral bleaching, which is affecting many reefs in equatorial waters further south.

On-Board Service and Experience
In terms of diving, there were no detailed dive briefings: no hand sign reviews, no emergency procedures were ever recalled, no expected dive profiles and times were ever mentioned. We only found the duration of the night dives after wondering underwater why many divers were surfacing after a much shorter time than normal. There were no post-dive discussions. For night dives, we were handed one torch each, and when asking if this was considered sufficient, the instructor joked about how we would be unable to handle 5 torches. One of our lights promptly failed underwater and one of us was handed the instructor's torch. Now we had a dive guide without a light... We had one more torch in our group on the next night dive, when, funnily, two of them failed.
There were only 18 dives planned and not 19 as advertised. To do 19 dives, one had to ask for it and get up very early on the last day (which was difficult for us to agree to as we became more and more tired due to the cabin situation).
The food offered on board was overall disappointing. It consisted of a lot of pasta with some kind of sauce, rather than Thai dishes. Apart from fruit, there was little fresh food. Frequently we were served refried leftovers from previous meals. Overall junk food, as it was referred to by a fellow diver.
In the evenings, some of the Danish divers on board showed their dive videos, some of which contained scenes like forcefully pulling a distressed moray out of its hiding place, or cutting off a starfish's leg to feed a harlekin shrimp, all to the great amusement of many including the AIDC management and staff.

Return to Ranong
Having lost two days due to engine problems, we had only one day left instead of three for a relaxing time on a closeby island (and catching somesleep, which we urgently needed). Despite being less than 5 minutes drive off the way to the dive shop, AIDC refused to drop us off where we would have catched the boat for the island. Instead we had to first return to the dive centre in town and then make our own way back to catch the boat. We missed our boat as a result.

Conclusion
Too bad to be true? That's how it felt. Be warned!
Judging from our overall experience, AIDC has to be considered a very unprofessional and unfriendly company. The entire trip felt like a terrible mistake, a horrible rip-off. We hope to never experience anything similar again and would certainly not recommend diving with AIDC.