A flow booster (8) is disclosed, shaped as a thick hydrofoil with an internal cavity (32), being aerodynamically inefficient on its own with a bulky relative thickness larger than 24 %, and being arranged to be positioned substantially below the rear part of a trawl door (37) comprising an overlapping sequence of several very slender hydrofoils (2), in such a way that the flow booster (8) forms a structurally connected integrated part to the hydrofoil (2) and impacts the upstream flow forcing it into a velocity boosted region (28) upstream of the flow booster (8) and to the pressure side (31) of the conventional part of the trawl door (1), such that the flow is pre-accelerated prior to running through the conventional trawl door channels (29) between the hydrofoils (2). Furthermore, a trawl door (39) comprising such a flow booster (8) and some uses of such a trawl door is disclosed.