A New Concept in Vessel Performance Monitoring.
Despite the occasional contrary opinion, weather routing is generally accepted as an evolved science which has a positive effect on the outcome of most passages. However, when a vessel arrives a day or so late having consumed an excessive quantity of bunkers the ship operator is given pause for thought. Was the delay a consequence of bad routing decisions ? Could the delay have been even greater without weather routing assistance? These questions will not be answered by most post voyage Performance Evaluation Reports.
Current performance evaluation is limited to a determination of whether the vessel performed in accordance with charter party warranties. If the vessel proceeded at a certain speed in good weather (normally defined as a wind speed not exceeding Beaufort force 4 or Douglas Sea State 3 ) the warranty is considered to be fulfilled. Vessel speed is corrected for periods of bad weather and an overall performance speed and bunker consumption is calculated. If the performance is within warranty limits the voyage is considered satisfactory. This method of evaluating a passage is referred to as Charter Party Performance
In practice, weather routing is a a decision making process which must balance the safety of vessel and cargo against the cost of fuel and daily hire . Adhering rigidly to the Least Distance Track (LDT) might save time and fuel but may subject the vessel to additional stress and increase the probability of cargo shift. Conversely, significant deviation from the LDT in a search for balmy weather will penalize the vessel operator with additional fuel and hire cost as well as increasing the generation of atmospheric carbon dioxide. The correct balance between these two extremes is referred to as Optimum Track Routing. Unfortunately, no method exists to determine with any certainty if the vessel actually followed the optimum track. This is interesting from the perspective of the vessel operator who is a “consumer” of routing services. Having purchased the services of an optimum track router the fact that the vessel actually followed an “optimum track” must be taken on faith.
Optimum Track Routing is such a nebulous concept that no word or
phrase exists in the weather routing fraternity to describe the level of
success achieved in following such a track. For the purposes of this
document the extent to which balance is achieved between safety and voyage
cost is
termed Tactical Performance.