The increase of ship dimensions in the latest years combined to the requirements regarding the reduction of environmental impact during the maintenance dredging and economic constrains in the Brazilian ports require technological solutions in order to optimize the safe accessibility of large vessels. Most of these ports operate under a static draft rule regardless the environmental condition acting during the maneuver, which is theoretically a conservative approach. The bay close or restriction is usually performed based on experience, which may fail in the absence of objective parameters to define the adequate underkeel clerance, providing some unsafe situations mainly in the presence of misaligned wind and swell waves and/or negative meteorological tides. The development of computational resources, monitoring systems and communication technology in the last years provided the basis for integration of these tools into an automatic draft computation system, called as ReDRAFT, which integrates the environmental conditions collected in real-time to the hydrodynamic model of the port and ship dynamic model customized for each specific maneuver (ship properties, loading condition, inbound/outbond) in order to define the safe underkeel clearance for the maneuver. Moreover the draft windows may be predicted based on the forecast models, which is also a powerful tool for planning. The numerical models allow more accurate predictions of the estuary environmental conditions, mainly waves, current and tide, which combined to the vessel numerical model can provide the ship motions in 6DoF. The ship motions on these large vessels are reduced for short period waves, thus allowing the increase the vessel draft. On the other hand the vessel motions are significant for long waves, requiring the reduction of the vessel draft in order to mitigate the risk of bottom touch. The system is already operational in Santos and Rio de Janeiro ports, two of the most important ones in South America, for vessels considered as critical according to the nowadays port traffic. The PIANC Report n° 121 – 2014 factors are considered in the computation of the maximum safety draft. The ship related factors considered are the squat, dynamic heels due to turning and wind, wave response and net ukc. In order to simplify the utilization and avoid mistakes in the input data, a large database of vessels was created and summarized in a user-friendly interface, where the characteristics of each specific vessel is defined based on the IMO number, BZ code or vessel name. If a new vessel is operating in the port, the vessel is included in the software database using Lloyd’s register information available in a standard “xml” format. The vessel hydrostatic/hydrodynamic characteristics are then interpolated using the software database if the dimensions are in the ranges of LOA, beam, depth and draft. The database contains the maximum wave motions of several points at the ship bottom considering a collection of wave periods, incidence direction, ship speed (encounter frequency correction), underkeel clearance, LOA, beam, depth, draft and ship type (tanker, bulk carrier or containership). The computations are performed in frequency domain using a higher order panel method based on spectral theory and a probabilistic approach. Since the ship geometry (stations) regarding each individual vessel is not available, some standard “design ships” are assumed and scaled to meet the desired LOA, beam, depth and draft, providing a NURBS (Non-uniform Rational Basis Spline) surface. The squat is computed based on literature regressions according to the Cb, ship speed (corrected to take into account the current effect) and channel geometry based on the the database of hydrostatic properties, the pilots expertise regarding required ship speed to keep an adequate maneuverability and the channel bathymetry. The heel due to turning is computed according to the lateral wind, the metacentric height provided in the database and the wind measurements. The heel due to turning is computed using the ship speed and the turning radius computed from the channel alignment. The maneuvering margin (MM) is defined based on the pilots experience to guarantee the safety according to the environmental conditions, ship dimensions and available tugs. The system is already operational in Santos Port since 2015 and in Rio de Janeiro port since October 2016 for validation in order to provide reliability to the system.