Although the contribution of artisans to the emergence of a “new science” in the Modern Age has traditionally been considered crucial, it has been only over the last decade that these communities have been studied in depth. Mastering a set of activities of a practical nature defined these professional groups, and allowed them to make their place in the societies of the time. Oceanic pilots were one of the artisanal communities that experienced a notable rise in prestige due to the usefulness of their practical knowledge for the expansion of the overseas empires. However, towards the end of the 15th century, this community was put under strain by the imperial machinery itself. In 1494 the Treaty of Tordesillas was signed, dividing the known world into two spheres of influence, one for Portugal and one for Spain. The demarcation line depended eminently on astronomical operations which were beyond the nautical skills of the pilots. Even so, this group was involved in the demarcation debates, having to confront a demand that was not part of the set of problems associated with their profession. Consequently, a practical and technical community was faced with an external constraint that radically affected established practices, and that put it in opposition to other communities, like theoretical cosmographers or crown officials. In this presentation we will analyze how these different professional groups adapted their skills to such "contra natura" demands, highlighting the epistemological frictions that permeated debates originally driven by diplomatic interests and imperial ambitions.