In this case it will probably the result of weather limits that have been set to ‘avoid’ instead of ‘warn’. It is likely that these limitations, especially when multiple limitations are set as a hard ‘avoid’ and limitations on especially beam waves, swell and wind. This can trigger the algorithm to ‘zigzag’, to avoid those conditions.
Another cause can be the following case. DTN uses a Route Network to safely navigate in waters shallower than 30 meters. It can happen that certain legs of the Route Network are not considered, for example due to draft restrictions or cargo type restrictions. This can lead to route deviations. Also, it can happen that the departure and/or destination location are positioned near one-way legs. In complex one-way leg situations, it can happen –with only particular departure or destination locations – that the algorithm will follow the first one-way leg that it encounters rather than crossing through it and connecting towards a one-way leg going in the other direction (green line). DTN is actively working on improving these cases near departure and destination locations.