I think that FL#30 does not have a black top spar buoy next to it. Perhaps Charlotte's father can verify this as he passes around Mink Island.
UPDATE: While passing by FL#30 on my way to the mainland this morning, I saw that there is a black top spar buoy next to the lighted buoy.
This makes sense as a boat operator would have no indication on how to pass this location by observation only if no spar was there.