Technically, going with shark anatomy, this is Blacktip’s first dorsal fin. The dorsal fin deviates significantly from the reference black tip shark’s lines. Antennas for both GPS and the cellular modem were added to the fin, with the “porch” on top of the fin housing the GPS antenna.
The think base of the fin is to provide reinforcement, as the fins are the most likely place for an under water impact. The fin is also filled with blown polyurethane, and is buoyancy neutral.
In the cross section above the rectangular recess in the middle of the tail is for the cellular antenna, and the GPS module rests in the well in the porch at the top of the tail. A LoRA antenna lives in the bolt on cap to the porch.
The two round chambers at the base of the tail are seats for two bolts held in place with epoxy. Those bolts are used to secure the tail to the Blacktip hull.