Naphtha Bomb
Ammunition, rare Market Price: 450 gp (1 talent for 4 bombs)
This sealed clay pot can be loaded into any siege weapon that can fire stones as its ammunition. Inside the clay pot is volatile mix of chemicals that explode into flames on impact. This incendiary recipe is called naphtha, and has been developed independently by both the Roman empire and Han Dynasty. Naphtha’s ability to burn at high temperatures, even when floating on the surface of the water, has made it one of the most effective and destructive weapons in the history of naval warfare.
Using a Naphtha Bomb. A Naphtha bomb may be used as ammunition in any siege weapon that can fire stones as ammunition, and uses the same attack bonus. On a hit, a Naphtha bomb deals 2d4 bludgeoning damage and explodes in a 20-foot-radius sphere. Each target within this area must make a DC 16 Dexterity saving throw, taking 8d6 fire damage on a failed saving throw, or half as much on a success. The fire spreads around corners and along the surface of any bodies of water, igniting flammable objects that are not being worn or carried. Such objects begin burning, as described on page 28.
If the attack roll misses, the Naphtha bomb fails to hit its target but still explodes. For example, if a catapult fires a Naphtha bomb at an enemy ship and misses its AC, the Naphtha bomb fails to hit the deck of the ship but still explodes as it lands in the water. Depending on the attack roll, the GM has latitude in determining whether a target might still be in the radius of an explosion, even if the attack roll failed to hit its AC.
Regardless of whether a Naphtha bomb hits or misses, it explodes and cannot be retrieved or used again.
Oops. Naphtha bombs are considered part of a ship’s “cargo” until they are used. If an encounter or effect (such as a storm or collision) specifies that any amount of your ship’s cargo is lost or damaged, roll a d6. On a 4-6, nothing else happens. On a 1-3, one of your stored naphtha bombs explodes, as described above, centered on the location the bomb is stored. If multiple bombs are stored in the same place, they do not necessarily all explode, since the outer shell of a bomb is not flammable.
Source attribution and license
Silk Road's Guide to Seafaring, printed pages 186, 187.