Ship characteristics: The characteristics of the ship that are taken into account in voyage estimating are size of the ship in terms of deadweight capacity, the bale and grain capacity of the ship, and performance details of the main and auxiliary engines (generators) such as consumption of fuel oil and diesel oil at particular speeds and when idle.
Time at sea :The time spent at sea must be calculated, as it represents a major cost element for the voyage. Apart from the fixed costs for ship operation (crew, repairs and maintenance, stores and lubricants, etc.), the variable cost of bunker fuel must be estimated and taken into account in the voyage estimate. To calculate bunker costs, the important parameters to be taken into account include the consumption of the engines (fuel oil and diesel oil), the speed of the ship, and the distance from origin to destination, including any deviations in between (total distance traveled).
The estimated voyage for any given trip commences from the end of the previous voyage. If the ship operator has managed to find a cargo at the port of discharging for the last voyage, then this is a bonus. Otherwise a ballast voyage needs to be estimated that commences with dropping the last outward port pilot and ends at the port of loading. Distance in nautical miles between the last port of discharge, the port of loading, and the port of final discharge can be found in a maritime Atlas. The vessel’s normal operating speeds when laden or in ballast are taken from the ship’s specifications. By dividing the overall distance of the route selected by the vessel’s speed (expressed in nautical miles per twenty-four hours), the ship operator will calculate the number of days it will take for the vessel to reach the discharging port. Different alternative routes will have an impact on distance and possibly on speed as well. Similarly, estimates will be influenced by the possibility of calling at ports to take on bunkers, transiting canals, or calling at multiple ports.
In estimating the time of the sailing voyage, allowances may be made for bad weather conditions (e.g., seasons, currents, tides) after reference is made to weather reports at particular geographical areas. Because bad weather conditions may cause a reduction in speed (say up to 15 percent), an appropriate allowance must be made. To calculate days at sea the total distance is divided by the product of speed and hours per day. For example if distance is sixteen hundred nautical miles and the ship sails at twelve knots, then 1600/(12 x 24) = 5.55 days.