We do get sharks sometimes but the waters are so cold they are very sluggish - nothing to worry about!!!
From what I have seen many RIBS will flip vertically - I think one reason could be that most of the weight is towards the back - I think because of the fear of stuffing the bow people are paranoid and go to the other extreme.
With correct weight distribution and trim it shouldn't happen.
Look at these videos and you will see what I mean.