That's interesting, I can see the edge of the platform catching and kicking up spray, but 18" in, I would be looking at something on the transom in that area, maybe a trim tab or bracket holding the platform? Looks like you might need to take a ride on the swim platform.
No thanks on the platform ride!!!!! I have no clue why it sprays 18" from edge. These boats seem similar and I have spent hours on both the 55 and the 58. It is near impossible to diagnose.