This paper describes the scientific features of an innovative technique to mass-produce monolayers of hexagonal close-packed structures (HCP) of particles (280–1100 nm). Our technique differs from a continuous roll-to-roll Langmuir–Blodgett (LB) process. It consists of a thin liquid film flowing down an inclined plane channel, the ramp, and entraining deposited particles floating on its surface to form a compact monolayer. Vertical sidewalls limit the entire flow. The main benefits of this technique in comparison with a standard LB process are a gentler push on the floating particles during the assembly and the prospect of better flexibility and scalability in the design of industrial applications. Our disruptive approach presents new control parameters and surprising but challenging hydraulic phenomena due to the flowing liquid. This paper investigates the hydrodynamics of this new LB-type design theoretically and experimentally. We propose an original theoretical prediction of the thickness of the liquid film flowing down the ramp without or with particles on its surface, including within the hydraulic jump region separating the liquid film whose surface is free of particles and the liquid film whose surface is particle-loaded. The experimental determinations of the film thickness obtained by a confocal chromatic technique and moiré topography agree well with our model. In addition, Bragg diffraction topography and false colour topography allow the HCP structure of the compact monolayer of particles to be quantified.