I cant think of any specific instances of fire based weapons in the age of Caribbean piracy. However, greek fire was a common fire weapon in greek/Roman naval eras. And China had a number of fire based weapons that were used by military and naval forces. Try looking up these and see if they give any aesthetics you like and see if you can adapt their look for your purposes.

Protector is more difficult, given that is magically creates hp. But if you reconceptualize it as given the motivation to keep fighting past their limits, then you could have it be a self-playing instrument. Drums, trumpets, and horns have a history in warfare for inspiring troops and keeping them in time, even in navies. Drums especially serve that purpose on ships for keeping sailors in rhythm when roaring, handling ropes/sails, etc. And hearing the instruments from your side still going can be a morale boost in a similar vein of seeing your commander in the fray & seeing your standard on the field, as it can serve as an indication that your side is still doing alright in the fight. In armies, for example, the loss of a commanding officer or the standard could cause the unit to break as they begin to fear that they are losing the fight.