Hey @Nixer992
Thank you for contacting Ubisoft Support.
In order to complete this achievement, could you test this:
- Buy a flame-thrower or a Pyrphorian Warship from Anne Harlow
- Attack an enemy ship and set it on fire
If it doesn't work on your first try, keep trying as it should unlock the achievement for you.
Alternatively, you can also build the Pyrphorian Warship after obtaining the legendary ship specialist item Slinky Sinistra, Warlock of Pyrphorian Warships and placing it into a Harbourmaster's Office within range of your shipyard.
Should you need additional support, please do not hesitate to get in touch with us again.
Thank you very much.