Many bulk trades are effectively one-way traffic with return voyages in ballast. However, while
consignments of such size may be available from oil and ore producers and acceptable at the
processing plant, this would not be the case for all bulk trades. Also, there is no financial
advantage in using large vessels if the loading and unloading rate is slow and the vessel is kept
unduly long in port. The ultimate constraint on vessel size remains the physical characteristics of
the port (channel depths, turning circles, lock gate dimensions, and berth lengths) and the routes
along which ships operate, particularly strategic passages. This has lead to well known capacity
standards such as Panamax1, and Suezmax2. A VLCC3 of 300,000 deadweight tons can transit the