Gauge Sap: current water level and draft

Water depth is not draught. Platform Zero Incidents cites a safety margin of 20–40 cm based on German case law, depending on the riverbed, vessel type and good seamanship. This is not a fixed legal minimum. Under-keel clearance is the space between the vessel and the bed. Dynamic squat while underway reduces that space. Viadonau gives 20–40 cm as a guide for squat. Meeting and overtaking can increase it further; MARIN describes an overtaking manoeuvre with more than 70 cm of squat. Sources: Platform Zero Incidents, CCR, German court ruling, viadonau, MARIN