all Norwegian supply ship including Ulstein design is designed to carry there massive superstructure. the superstructure on these vessels are usually very light weight, even the helipad is designed to be as light as possible. adding the radar mast on top of the superstructure will add to mush weight up top, thus she will lose her stability (increased chance for capsizing).
If Ulstein was to design a vessel like this they would do this:
Red: lowering by one deck (deleting one deck)
Green: moved more aft.
Orange: on modern supply ship like the Ulstein designed supply ship, this hatch is where the RHIB and free falling life boats are stored. you don't need that since you have an large RHIB bay aft.
That is just one of the many things they will do to it. These ships type are designed on the limit for what they can handle, more than that, you have an submarine. if you add something more on top you need to remove something.
If you really want to save weight on the crane. Here are a new crane designed here in Norway, where all it's equipment are build inside the crane instead outside of it. It also use a new type of fiber rope then the old steal wire: