Demersal Seining is an active fishing method applying two seine ropes and a seine net. The seine ropes and net are laid out on the fishing ground in a way that they encircle an aggregation of fish. During the fishing operation, the fish is gradually herded by the seine ropes into the path of the net. Knowledge about how the size and shape of the area encircled by the seine ropes gradually change during the fishing process is important for an efficient fishery. The purpose of the project "Danish Seine: Computer based Development and Operation" (MAROFF-2 project no. 225193 / FHF 900861), funded by Research Council of Norway (RCN) and Norwegian Seafood Research Fund (FHF), is to develop software tools to investigate Demersal Seine fishing. An important aspect of the research is to be able to simulate the physical behaviour of the seine ropes during the fishing process. Therefore this report: i) formulates a model for the physical behaviour of seine ropes for demersal seining; ii) describes the implementation of the model into a set of software tools that together enable simulation of seine rope kinematics for demersal fishing operations; iii) validates predictions made using the simulation toolbox against flume tank experiments.