Interesting 'goatee' under the bulb... grounding reinforcement?
That's the keel Martin , all the bigger boats are built with that step in them now , the box keel is filled with lead to keep the inside of the hull clear for equipment and , in the case of the Research , bigger tanks for holding fish. These tank boats all have 12 large refrigerated sea water tanks to hold Herring/Mackerel/Blue Whiting , normal ratio is 40% water 60% fish and the water is recirculated to keep the fish fresh.
Engine room is large on these boats so they have the space for huge chilling units to keep the fish fresh.
^^ Tanks kept empty in harbour , tanks filled with water so it can be chilled only once they are out of the harbour