Our Prevoyage Brief is just the beginning!


Our earlier blog ‘April Gains Time‘ detailed that prevoyage brief (PVB) planning for optimal routing is a net benefit service of several orders of magnitude.  Continuing the theme, here is another example that reflects a route adjustment linked to Tropical Storm Henri in August which showed significant cost differences between options.

We treat every voyage as unique as there are multiple factors at play in optimising any route.  Once underway the process is reiterative as each model update (most global models are run 4 times per day) can result in further adjustments as longer term forecasts (with greater uncertainty) move into the near term (more certainty).  This is especially true for cross-ocean voyages or when predicting and tracking tropical storms or rapidly changing weather scenarios.

Avoiding Tropical Storms

The earlier that one can adjust a route, then in general terms the greater the benefit. However, longer lead times can mean greater model uncertainty often leading to a dilemma of whether to react early or delay until more certain (less risk).  Fig.1 details a voyage approaching the US Eastern Seaboard on 18 August 2021 at a time when the models were having difficulty forecasting the track of Tropical Storm (downgraded from Hurricane status) Henri with some model members starting to show a more westward movement than previous.

Figure 1. PVB detailing three different route options shown in Figure 2 for a voyage from Europe to Boston for 18 August ahead of Tropical Storm Henri.

The route options based on the expected track of the system at the time were:

Alt-1(Pink) – the master’s intentions to avoid TS Henri: RL from 46.3N/42.1W to near 40N/60W, then RL near 40N/65W, then most direct to Boston. 

Alt-2(Green) – a GC route to near 40N/70W, then most direct to Boston.

Alt-3(Brown) – most direct routing to Boston via coastal routing S of Nova Scotia (remaining north of Alt-1 and Alt-2).

Alt-2 and Alt-3 offer two alternatives that have longer time/distance within the ECA (1008 nm and 999 nm respectively) but which reduce the distance through the water. With similar weather factors on Alt-1 and Alt-2 but a slightly less current factor with Alt-2, the PVB clearly shows Alt-3 is the best route in this situation as it saves 210nm/16.2hrs distance through water (DTW), even though the ECA distance is 712nm longer compared to Alt-1.

Figure 2.  Left: 18 August 2021: Alt-1(Pink), Alt-2(Green), and Alt-3(Brown) shown together ahead of Tropical Storm Henri. Centre: Forecast for 22 August 2021. Right: Forecast for 23 August 2021.

The savings calculations for these options are based on global prices at the time and shown at Fig. 3 where: VLSFO ($528.5/mt); MGO ($613.0/mt); and an On-Hire cost of $14000/day.  The subject vessel was warranted an FO/GO consumption of 26.5MT/day.  Alt-3, despite steaming longer in the ECA, saved a total fuel cost (FO and GO) of $6394.67 and on-hire cost of $15611.67 due to the 15.8hrs less steaming time compared to Alt-1, resulting in a Total Voyage savings of $22,006.34 on the remainder of this voyage! 

Figure 3. Cost breakdown of options for the remainder of the voyage.

While the belief of steaming outside ECA will generally save/cut costs, this is not always the case. From Fig 3 proceeding in the ECA saved more than the cost to burn the MDO/GO fuel.   By taking Alt-3, the vessel also saved roughly 56.06567MT in Total Emissions (including CO2, SO2, and NO2) – the equivalent of driving your car 140,904miles, charging your smartphone 6,819,977 times, or saving 68.7 acres of forest in one year!

When is routing through ECA worth it?

Like the above example of routing through the ECA to avoid a tropical system, the benefits of carrying sufficient MDO/MGO onboard can also provide savings during the fall/winter season enabling one to route north of any heavy/adverse weather conditions associated with the North Atlantic gale/storm track should the opportunity arise.  

The importance of the Prevoyage Brief Planning

Our PVB tool is flexible in use and can be used to show potential savings for any voyage even when circumstances change once enroute as each is treated as unique.  In this example the ship had sufficient MDO/MGO to steam within the ECA (Alt 3) or use the longer route to steam astern of TS Henri (Alt 1) or a combination of both.  

Of course not all route adjustments are done to save time/costs.  It is not uncommon that an optimal route may need further adjustments as the models refine the forecast, such as the centre of a storm moving closer to the original track or even the system deepening more than originally first thought.  This can result in adding extra distance to the route to avoid bad weather, increase safety, and prevent damage.  The converse is also true in that the models may have overdone the original intensity and later model runs show less intensity allowing the route to be adjusted which may well save time over the original route.  If one then includes operating costs, arrival times, and plethora of other factors, it is true that each voyage is unique, and we treat them as such.

If you would like to take advantage of this service then please reach out to us and we would be happy to assist!

Stay connected and safe.

About The Author

Share via
Copy link
Powered by Social Snap