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Similan Islands and Koh Bon stand out for advanced wall dives due to their dramatic limestone ridges and granite pinnacles dropping to 40+ meters, drawing manta rays, reef sharks, and pelagics via strong currents. Koh Bon's west ridge, north of Similan No. 9, offers sheer walls unlike the Similans' boulder reefs, creating unique drift opportunities. This national park delivers world-class topography and biodiversity unmatched in Thailand's Andaman Sea.[2][3][4]
Top sites include Koh Bon's West Ridge for manta cleaning stations, East Wall for coral-crack critters, and Similan walls like Shark Alley for shark drifts. Liveaboards provide 11–15 dives over 2–4 days, hitting Koh Bon, Tachai, and Richelieu Rock. Expect 10–30m visibility, slopes from 10m to sandy bottoms at 25–40m, suited for intermediate-advanced drifts.[1][2][3][5]
Dive from late October to early May, avoiding the June–October monsoon closure; November–March brings calm seas and peak mantas. Prepare for currents requiring drift skills, depths to 45m, and park fees of 400–700 THB. Liveaboards from Khao Lak ensure access, with day trips limited to certified divers.[1][2][5]
Local Khao Lak dive crews foster a tight-knit community of Thai operators and global adventurers, sharing manta spotting tips passed down seasons. National park rules enforce no-touch policies, preserving sites for sustainable dives. Insiders chase Koh Bon at dawn for undisturbed rays amid limestone arches.[3][6]
Book liveaboard trips 3–6 months ahead for November–March peaks, as spots fill fast; opt for 3–4 day itineraries covering Koh Bon and Similans for 11–15 dives. Certified Advanced Open Water divers get priority, with courses available on board for skill-building. Day trips from Khao Lak work for Wednesdays/Sundays but limit exposure.
Train for strong currents and deep profiles up to 40 meters; carry redundant gear like extra masks and surface signaling devices. Pack seasickness meds for overnight boats and reef-safe sunscreen for topside. Brief with operators on manta etiquette to avoid disturbance.