Coëtlogon's engine failures drove a lesson in compass protection

Coëtlogon was the privately built member of the class, constructed at the Saint-Nazaire yard founded by Scottish engineer John Scott. Her propulsion system failed during the first trials and had to be replaced completely. Third-category reserve meant that the navy kept her on the books while doubting she would ever enter service. New engines were not installed until 1893, and excessive friction halted the next trials because vibration made the ship's compasses unusable. The episode showed that compasses needed protection from mechanical shock as well as magnetic interference and contributed to improved instrument isolation. Coëtlogon finally reached 20.4 knots under forced draught in June 1894 but still required further changes before entering service that August, roughly seven years after being ordered. Her immediate assignment to active duty reflected how much time and money the navy had already invested in obtaining a usable ship.