it looks like the plate that the top edge of the dolphin striker pushes against at the hulls under the main beam.
Sorry for the not-so-technical terms.
It is not the plate on the hull. That tang has oval ends, & is much longer than width. It is also riveted onto the hull, the one in the photo does not appear to have any rivet holes.
There is no reason to have that under the beam, there should be nothing,(other than perhaps some bedding material to fit the beam exactly to the hull.
What year is your 5.2?
Some of the older ones, with the smaller gauge DS rod had a small plate where the rod rested on the V strap.
I have not seen such a piece on either of the older 5.2 we wrecked, the 5.7 or 5.0, & certainly not between the beam & hull. It would just ig into the hull if placed there, & not allow the hull to fit flush with the beam.
-- Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap --