This expression relates to the maximum draught enabling the ship’ to pass over a “bar”, for example, the Martin-Garcia bar in the River Plate. A “bar” is a restriction in the depth of water, caused by a build-up of sand or silt on the bottom, in a river or across the entrance to a harbour. The quantity of cargo, which can be loaded in the up-river ports of the River Plate, will depend entirely upon the water level at the time when crossing the bar. In the event the vessel has too great a draught, it will be necessary to discharge part of the cargo into lighters, which cargo will have to be reloaded after passing the bar. This extra handling of cargo is an expensive operation in the River Plate. In most cases, a vessel, which has been loaded in up-river pans to bar draught, will complete loading downriver, after having crossed the bar, at a lower rate of freight. The quantity of cargo, which can be loaded down the river, in order to bring the vessel down to her marks, must also be considered. It is obvious that if a small quantity is involved, shipowners may decide to refrain from completing below the bar, taking into account extra port charges, delay etc. assuming they are not committed to loading a full and complete cargo.
Such ports are called “bar ports”. Vessels, which are prevented from crossing the bar through their draught exceeding the maximum depth of water on the bar, are “bar bound”.