A new genre of treatises on practical seamanship emerged in eighteenth-century Britain. Authored by a group of seamen with decades of experience on the lower deck of merchant and naval vessels, these texts represented the ship as a machine, and seamanship as a form of mechanical experiment which could only be carried out by deep-sea sailors. However, as this article finds, this group of sailor–authors had only a brief moment of authoritative legitimacy before their ideas were repackaged and promoted by (...) land-bound authors and naval officers, and the progenitors of the ‘science of seamanship’ were deemed unfit participants in its ongoing practice. This article explores this brief moment, taking seriously the ideas and influences of the maritime milieu which spawned it, and arguing that the codification and circulation of ‘useful knowledge’ in eighteenth-century Britain often hardened social hierarchies. Examining seamanship forces us to question the progressivist linear trajectory of an increasingly open scientific culture during this period, and to focus instead on a repeating pattern in which the working knowledge of labourers and artisans was appropriated and its original practitioners denigrated. (shrink)