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Koh Bon, a limestone islet 20km north of Similan Island 9 within the national park, stands out for drift-diving due to its dramatic ridges and walls shaped by relentless currents that funnel manta rays. Unlike granite Similans, its sloped reefs from 10-40 meters host hard corals and cleaning stations where mantas linger. Strong to medium drifts make every dive dynamic, with 30-40m visibility drawing advanced divers worldwide.[1][2][3]
Top drifts circle the west ridge for mantas, pinnacle swims for depth thrills, and northeast slopes for fish schools amid sea fans. Liveaboards chain multiple profiles daily, while day boats from Phuket hit 2 dives. Expect barracuda, tunas, and occasional whale sharks alongside routine manta magic.[1][4][6]
Dive October 15 to May 15; November-April offers calmest seas, 28-30°C water, and peak mantas. Currents range mild to strong—hook up on ridges, deploy SMBs always. Prepare for 1.5-3 hour boat rides; advanced certification required for depths and flows.[2][3][5]
Local dive crews from Khao Lak share insider drops based on daily currents, fostering tight-knit groups on liveaboards. Park fees support conservation, with operators enforcing no-touch rules to protect mantas and reefs. Divers bond over post-dive tales of "manta shows" at communal meals.[1][3]
Book liveaboards or day trips 2-3 weeks ahead, especially for peak season November-April, as national park limits daily divers per site. Opt for certified operators from Khao Lak piers for 2-dive day trips or multi-day trips covering Similans and Koh Bon. Check weather forecasts, as swells close sites October-May outside calm windows.[2][3][5]
Practice current dives beforehand; Koh Bon demands strong buoyancy and finning skills for ridge drifts. Bring reef-safe sunscreen, motion sickness meds for the 75km boat ride, and extra weight for potential strong currents. Rent gear on-site if needed, but confirm advanced or deep certification for sites over 30 meters.[1][4][6]