Located 55 miles (100km) south of Chalong Bay, Hin Daeng and Hin Muang offer some of the only (and the best) wall diving in the Andaman Sea. When conditions are right, the pinnacles of Hin Daeng and Hin Muang triumph over anything in the Similan Islands.
The best way to visit these islands is on a short liveaboard from Phuket. Thee are several boats which offer nice quick itineraries to these sites. You can also dive them by speedboat from Phi Phi and Koh Lanta if the weather is just right, but the fact is, just like the Similans, these dive sites are a long way from shore and a speedboat can be a bumpy, expensive and often unsafe option. A liveaboard offers you more diving, more comfort and a higher safety level.
There are four principle places for diving in this area south of the Phi Phi Islands. These are Koh Ha Yai, Koh Rok, and the famous Hin Daeng and Hin Muang; then there are several islands inshore from Koh Rok and just south of Koh Lanta. Koh (or sometimes spelled "ko") means island in the Thai language. "Hin" means rock or pinnacle. Fortunately, none of these dive sites were damaged by the tsunami which hit Thailand and the rest of the Indian Ocean in late 2004.
Koh Ha is a small group of islands almost directly west of Koh Lanta. These tiny islands, separated by channels over 50 meters deep, jut straight out of the Andaman Sea. However, unlike at Phi Phi, the water here is ordinarily quite clear and visibility frequently exceeds 25m. The highlight of diving here is a series of caves, or caverns on the largest of the islands, Koh Ha Yai. The caves are safe to enter, even without a light, as the entrances are large and there is only one way in and one way out. The best part of entering these caves is that you can surface inside the island to view stalactites hanging down from the ceiling over 30m above the surface. The quality of light filtering through the water from the entrance is magical and often you can see big fish swimming back and forth in front of the entrance.
Moving inshore to the south of Koh Lanta, the water clarity deteriorates, and the diving is quite shallow. There are a couple of nice dive sites, and one particularly interesting place to explore called the Emerald Cave (ถ้ำมรกต or tam morokot) in the Bay of Trang, where at high tide the diver can swim through a large cave underwater to surface in a perfect little lagoon complete with its own white sand beach and splendid tropical jungle. Once inside, you are surrounded by tall cliffs, and the only way out is through the cave. Therefore, an experienced guide who knows the area is essential for safe exploration. There are bungalows and resorts and a dive shop or two in this area at Koh Muk and Koh Hai (Ngai).
Koh Rok, about 25km south of Koh Ha, are two sister-islands separated by a narrow channel about 15m deep. These islands, nok and nai (outside and inside) have some of the prettiest beaches in Thailand and are completely devoid of inhabitants since they are part of the greater Lanta national park area. The islands are named for a small, furry mammal called a "rok" in Thai, and this animal, along with monitor lizards, can be observed on-shore-with a little patience and a bit of luck.
The diving here is relatively shallow, with the best corals and fish life living above 18m (60ft). The bottom is composed of mostly hard corals, with small areas of soft corals at deeper depths. Black tip sharks patrol the reef shallows and hawksbill turtles are sighted regularly. But the main reason for stopping in Koh Rok is that it is the perfect jumping off point for trips out to Hin Daeng and the islands have ideal anchorage in all weather. Most yachts on the way to Phuket stop here as it's very pretty and the islands offer protection from almost any weather.
The sole reason that diving has become world class in Koh Lanta and Krabi are two pinnacles that lie approximately 25km southwest of Koh Rok. Hin Daeng (red rock) and Hin Muang (purple rock) offers everything a diver could want, from dramatic walls and big fish action, to lush tropical underwater gardens.
Hin Daeng is easily found since it protrudes about three-meters above the surface. Although not very impressive topside, underwater the rock is huge. The southern side descends–straight down–to over 60m (200ft) forming the most radical vertical drop in Thailand's seas. The wall is dotted with light growths of soft corals and a few seafans, but is otherwise devoid of life. On the eastern side where the slope is more gentle, two long ridges descend into the blueness and if the currents are favorable it is possible to swim along these ridges down to 40m or more. Here the soft coral becomes more lush and tall, and huge schools of jacks sweep past the ridge, surrounding the diver with a shimmering wall of silver. Ascending to the shallows we see needle fish (longtoms) skip along the surface. Barracudas stalk their prey through the clear water. Swimming between the three large rocks that form the surface view of Hin Daeng, large schools of fusiliers dart to and fro as if they are afraid of the water surging through the channels.
Hin Muang, located just a few hundred meters from Hin Daeng, lies completely submerged. What surprised us the first time we explored the rock was the incredible amount of marine life that clung to the rock. It is as if the rock were located in another ocean and not just a short distance away from the relatively barren Hin Daeng. The name derives itself from the thick purple growth of soft corals that are everywhere. The rock itself is approximately 200m long and less than 20m wide, and is shaped like a loaf of bread with steep, vertical sides and a rounded top. The walls are decorated with large seafans of red, white and orange. Clouds of glassfish, or silver-sides school around the fans and rocky outcroppings. Carpets of anemones cover the shallower sections of the pinnacle.
One July, the water was so transparent and the sea so smooth that I could see clearly the splash of someone throwing the dregs of their coffee overboard with puffy white tropical clouds as a back-drop-from a depth of over 45m (150ft)!
Whalesharks are one animal that we see repeatedly around these pinnacles and many years we see them on most of our trips there. Though we see whalesharks less now than we did in the 1990s, they are still around on a regular basis. Manta rays are rapidly becoming more of a common reason for diving in Hin Daeng as the tops of the pinnacles act as cleaning stations for these giants.
Whalesharks are seen more often at pinnacles than around islands simply because a diver has an easier time spotting them at a small rock rather than a long dive site. It's not that they are here more often than other places; it's just easier to spot them here. It's a fine distinction, but something important to understand. Many people think there is something environmental special about Hin Daeng and Richelieu Rock, but this is not the case. It's geology, not geography.
On many occasions we swim with gray reef sharks in the deep blue water off Hin Daeng and Hin Muang. This is the only place in Thailand where I have seen more than 10 gray reef sharks together at one time. Gray reef sharks are full-bodied sharks, powerful and sleek, and are often confused with blacktip sharks because of their similar markings. However, unlike their cousins, these sharks are true pelagic animals, and swimming with them is a stirring, emotional experience. On one occasion, I managed to hover within two meters of a group of these sharks who ignored me in favor of a large school of jacks; apparently they were more mouth-waterig.
Hin Daeng (Red Rock) is marked on Thai nautical charts thusly and we do not know where the name came from although I suppose fishermen named it because when the sun is setting the rock does glow a reddish color. During the day it's brown, but "Brown Rock" doesn't roll off the tongue nicely in either English or Thai.
Hin Muang (meuang) was named when we found the dive site in about 1991 when my company started doing regular trips there. At that time, there were not many soft corals on Hin Daeng, it was mostly barren with some large sea fans deeper on the wall. Over the years we have come to know that the corals come and go. Soft corals grow very quickly, so if they disappear, they–so far–come back again nicely. Hin Muang, on the other hand, was so full of soft corals when we found the rock that it was promptly named Purple Rock because the whole thing was completely purple! (We searched for months and finally found it one day by accident; we thought it was further out to sea than it turned out to be.)
As it turns out, Hin Muang's soft corals also come and go. Some years they are very lush and abundant, others less so. This may be because of the nature of these types of soft corals or it could be caused by humans and destructive fishing practices. Either way, they always recover.
John Williams has written, co-authored, or contributed to four diving guides on Thailand, the Mergui Archipelago, and the Andaman Islands. These are the award-winning Lonely Planet Diving & Snorkeling series, Periplus Editions Diving Southeast Asia, Asian Diver Scuba Guides and Singapore's Times Edition Diving Thailand. He has lived in Phuket and dived in Thailand's waters since 1987.