Thailand Aggressor Liveaboard Review – Similan Islands, Thailand

Liveaboard & Accommodation

The Thailand Aggressor operates its North Andaman Sea itinerary out of Thap Lamu Pier in Khao Lak — a small coastal town on the mainland roughly 80 kilometers north of Phuket. Most flights into the region route through Phuket International Airport (HKT), with the transfer to Khao Lak taking between one and one and a half hours by road. I arrived a few days before the liveaboard departed and stayed at the Kantary Beach Hotel in Khao Lak, which worked out well as a base before boarding.

The Thailand Aggressor is a 115-foot yacht — a good-sized liveaboard for a week of diving — accommodating 16 guests across eight staterooms with a crew of twelve. The boat runs across three decks: the lower Dolphin Deck housing the engine room, the main deck holding the guest cabins and dive operation, and the upper deck where meals are served and the hot tub is located. The main salon on the main deck is air-conditioned and serves as the briefing room, photo and video review center, and general gathering space between dives.

I stayed in one of the six Deluxe Staterooms on the main deck, configured with two side-by-side beds, mirrored cabinets, a wardrobe, and enough vertical storage to keep a week’s worth of gear organized. Every cabin has independent air conditioning, a private head and shower, a 22-inch flat screen TV loaded with films, a hair dryer, fresh towels, and bathrobes — the last of which are more useful than they sound when you’re doing four or five dives a day in warm water.

Meals were served five times daily on the upper deck: a light breakfast before the first dive, a full cooked breakfast afterward, a buffet-style lunch, afternoon snacks between dives, and a three-course sit-down dinner each evening. The focus was on sustaining energy through a demanding dive schedule — carbohydrate-heavy lunches, fresh local seafood and proteins at dinner, and enough snacks between dives to keep everyone moving. All meals, snacks, and beverages are included.

Dive Operation & Facilities

The dive operation aboard the Thailand Aggressor is built around a skiff-only model — the mothership stays anchored in a protected area while two 9-person skiffs ferry divers directly to each site. For a destination like the North Andaman Sea, where many of the best sites are submerged pinnacles with meaningful current, this approach makes a real difference. The skiffs allow for precise drops directly over the target, and the crew hands off camera rigs once you’re in the water, which is a small detail that matters when you’re managing a housing in a current.

The dive deck on the aft of the main deck is well laid out for a full complement of sixteen divers. Each guest has a permanent assigned station with a tank rack, and the crew handles tank fills in the racks between dives — meaning you never have to break down your regulator setup unless you’re changing tanks. It keeps the workflow clean and reduces the kind of O-ring wear that comes from repeated assembly and disassembly over a week of heavy diving. A camera table on the dive deck and warm freshwater showers on the swim platform round out the setup.

Briefings were clear and thorough, covering site layout, expected conditions, and marine life to watch for, with dive site maps displayed on the salon monitors. The crew was friendly and knowledgeable throughout the week. The briefing for Richelieu Rock in particular set accurate expectations — strong current, a dense pinnacle, and the kind of marine life density that requires slowing down rather than covering ground. The overall atmosphere on the boat struck the right balance: structured enough to run 24 to 25 dives efficiently over the week, relaxed enough that it never felt regimented.

Diving & Marine Life

The North Andaman Sea itinerary covers three distinct areas over the course of the week: the Similan Islands, the open-water pinnacles of Koh Bon and Koh Tachai to the north, and Richelieu Rock inside Surin National Park. The route has a natural progression to it — the Similans ease you into the rhythm of skiff diving and site variety, and the itinerary builds toward Richelieu Rock as the centerpiece of the week.

One thing worth knowing before you go: the season runs November through May. The national parks close during the southwest monsoon from June through October, so there’s no flexibility on timing the way there might be with a land-based operation.

The Similan Islands

The Similans offer two distinct types of diving depending on which side of the islands you’re on. The eastern slopes are dominated by hard coral reefs with gradual gradients, while the western side is defined by massive granite boulders that form canyons, arches, and swim-throughs. Elephant Head Rock — locally known as Hin Pusa, located between Islands 7 and 8 — is the signature site. It’s a network of swim-throughs between 15 and 30 meters, with whitetip reef sharks resting on the sandy bottom between boulders and soft corals covering the upper sections of the rock.

Anita’s Reef served as our check dive, and while it’s sheltered and straightforward, it holds its own on macro. The coral head known as the Whole Roll — named for how much film photographers used to burn on it — was covered in glassfish, cleaner shrimp, and nudibranchs.

What I didn’t expect across the Similans was the octopus activity. We were diving at the start of the octopus mating season, and they were everywhere — on coral heads across nearly every dive. It was one of those timing-dependent encounters that you can’t plan for, and it added a layer to the Similan dives that I wouldn’t have anticipated going in.

Koh Bon and Koh Tachai

Moving north, the character of the diving shifts. Koh Bon is defined by an underwater ridge that extends out into open water and functions as a regular cleaning station for oceanic manta rays. We spotted mantas during our time there, though they stayed well out in the blue and didn’t come close enough for a meaningful encounter — that’s the nature of open-water pelagics, and it doesn’t diminish the site. The ridge is worth diving regardless.

Koh Tachai Pinnacle is the most current-exposed site on the itinerary. The flow brings in large schools of chevron barracuda and bluefin trevally, and the pinnacle is a known whale shark corridor during the peak months of February and March. It’s a challenging dive, but the current is the reason the marine life is there at all.

Richelieu Rock

Richelieu Rock is an isolated limestone pinnacle east of the Surin Islands, and it’s the site the entire itinerary builds toward. The formation rises from 35 meters to just below the surface and is encrusted wall to wall with purple soft corals and anemones. The current at Richelieu was strong during our visit — the briefing prepared us for it, but it still demands attention. It’s the kind of site where you pick your position and work it rather than trying to cover the whole structure in a single dive.

The marine life density at Richelieu is unlike anything else on the itinerary. Harlequin shrimp, ornate ghost pipefish, seahorses, and flamboyant cuttlefish on the macro end. Giant trevally and dogtooth tuna hunt the surges near the top. The Thailand Aggressor typically dedicates a full day to the site with four dives, and by the end of the day the changing light and shifting current had genuinely altered how the fish were behaving between dives — it’s a site that rewards the repeat visits in a way that not every destination does.

For photographers and videographers, Richelieu Rock is the reason to book this itinerary. Everything else on the route is excellent, but this is the site you’ll be thinking about when you get home.