The technique of model studies on fishing gear, developed by the staff of the Department of Fishing Techniques, is employed in the field research carried out in a lake with the assistance of a catamaran as a gear model towing craft. A particular attention is paid to the functional coupling of a vessel, trawl, and rigging which makes up a complete trawl system. The work presented was carried out at the Model Research Station in Ińsko, the Station being a unit of the Faculty of Marine Fisheries and Food Technology, Academy of Agriculture, Szczecin. The paper introduces study techniques and some results of experiments on effects of pelagic trawl mouth construction and opening on geometry- and resistance-related trawl characteristics.