The traditional watercraft of Thailand's sea nomadic peoples—the Moken Kabang and the Urak Lawoi Prahu—serve as intangible expressions of their distinct maritime cultures. The Moken's relationship with marine environment exemplifies biocultural system wherein boats function not merely as technological object but as embodied repositories of ecological knowledge, cultural practice, and adaptive strategies. Traditionally constructed from locally-sourced materials, the Moken traditional boat represents a dynamic interface between human culture and marine ecosystems.  This traditional boat or Kabang defined not only Moken’s daily livelihoods but also their cultural identity, spiritual worldview, and social organization.  We also explore the social fabric maintained through boat ownership and sailing communities, and the role of these traditions in asserting cultural autonomy.    The Urak Lawoi, despite their nomadic and settlement patterns differing from the Moken—maintain a sophisticated maritime material culture wherein boats or Prahu remain central to their identity and livelihood. The Urak Lawoi have developed boat designs and technologies that reflect accumulated ecological knowledge and adaptive problem-solving.  Boat anchor string, for instance, are deliberately crafted to break and release when the anchor becomes wedged in underwater crevices. This design represents a pragmatic way of working with unpredictable marine situations.   This presentation adopts a biocultural lens to examine how Moken and Urak Lawoi boat-building and sailing traditions integrate biological knowledge, ecological understanding, and cultural meaning as an interconnected system.  Boat’s design, construction materials, and navigation techniques encode generations of accumulated environmental observation and adaptive resource management.  We will also examine the consequences of disrupting these biocultural systems through modernization, commercial fishing pressures, and marginalization, which threaten both cultural heritage and marine ecosystem.