The crack in the bulkhead looks serious, but it would help if we could see photographs of the ends of the crack. From the photograph there dosen't seem to be any loose fibers around the edges of the crack. The lack on loose fibers may mean it is a new crack, just happend, or its an old crack, but the bulkhead is not flexing. Also from the photograph, we cannot see how far the crack extends toward the hull. The bulkheads strength is in the outer 3" to 4" next to the hull. If the crack extends into this area, 3" to 4" next to the hull, and is showing loose fibers, the hull is flexing and needs repairing. It is quote common to see large holes in the center of bulkheads, these holes are there to reduce the bulkheads weight.
If the ends of the crack are showing rough fibers, the area is flexing under load and needs reparing, but if the ends are clean, it is most likly and old crack.

S Beach