Eighteenth-century naval ships were impressive infrastructures, but subjected to extraordinary strain. To assist with their "voyage repairs," the Royal Navy gradually established numerous overseas bases, displaying the power, reach, and ruthless logistical efficiency of the British state. This article, however, is concerned with what happened where no such bases (yet) existed, in parts of the world falling in between areas of direct British administration, control, or influence. The specific restrictions imposed by technology and infrastructures have been studied by historians interested in naval strategy, but they can also help to reframe national narratives of power or observe the transnational interactions surrounding access to knowledge and resources. This paper discusses the material, cultural, and diplomatic constraints that could appear when vessels, and especially "discovery ships," sailed in strange waters or sought technical assistance in allied ports. I argue that the "mortification" of some commanders at their vessels' unfitness for service was an important - and often neglected - element on the palette of emotions undergone by voyagers, capturing their strong sense of ultimate material powerlessness. Such frustration even became embedded in imperial cartography, as shown by the case study of Matthew Flinders. This perspective highlights the limits of naval technology, complicating imperialistic "success stories" and better reintegrating the navy into the history of maritime travel and transportation, from which it is often singled out.