The dart is the penetrator. The shank (the metal point the dart rests on) drives the dart into the fish using the kinetic energy imparted to the harpoon shaft when you throw, as
>>2697027 said.
The dart is a separate piece so that it can rotate freely once it sticks into the target without snapping the shank. This video explains pretty well how to rig a harpoon line.
https://www.youtube.com/watch?v=HhpEaVboPEsAlthough it's about a specific brand/model, the rules apply to any harpoon. I suggest using a teak dowel for your handle.
t. OP of the thread
