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The optimal trajectory from Calcutta port to Mumbai port is charted for a tanker transshipping from the East coast to the West coast of India during rough weather. Rough weather is simulated over Indian seas using the state-of-the-art WAM numerical wave model (WAMDI Group in J Phys Oceanogr 18:1775-1810, 1988, assimilating satellite (IRS-P4) wind fields. These simulated wave fields and two-dimensional (2D) directional wave spectrum are an absolute representation of the irregular seaway. Hence, the same for the monsoon month of August 2000 formed the input basis for this study. Loss of ship speed due to the wave field (i.e., nonlinear motion of the tanker in waves) and associated sea-keeping characteristics in the seaway are estimated (Bhattacharya in Dynamics of marine vehicles, Wiley, New York, 1978). The approach adopted in this paper is unique in that it takes into account both voluntary and involuntary speed reductions of the ship. It helps in ship tracking by the optimum route using inverse velocity as the weight function for the path in an efficient way. Dijkstra's algorithm [Numer Math 1(3):269-271, 1959] is applied in an iterative manner for determining the optimum track. The optimum track information has broad scope for use in modern shipping industry for obtaining safe and least-time routing by avoiding schedule delays with economic fuel consumption.

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The cyclone wave parameters are predicted using Young's parametric hurricane wave prediction model. The input cyclone tracks for this work are obtained from Fleet Naval Meteorology and Oceanography Center, USA. Extreme value analysis is carried out to obtain the wave heights and periods for 1 in 5, 10, 50 and 100 years return periods, respectively. The deep-water hindcast wave corresponding to 100 years from probable directions are allowed to propagate to Visakhapatnam coastal waters using nearshore spectral wind-wave mode. The offshore wave height for one in 100-year return period is 11.9 m, and the corresponding nearshore wave height at 10-m water depth varies between 4.6 and 5.6 m depending on the directional spreading. Weibull distribution is chosen to fit the 24 cyclonic data sets over a total period of 30 years (September 1972 to November 2002. This paper demonstrates usefulness of Young's wave model for deep-water extreme wave hindcasting. Further, the results of the present study would be highly useful for assessing the design wave height for Visakhapatnam coast.