**6.3 Suboptimal vehicle routing in a stationary sea current**

Here we show another example of vehicle routing in the Northwest Pacific Ocean containing the environmental uncertainty of *σ* = *4Ucm*. Vehicle trajectories are shown in **Figure 15**.

In this example, a vehicle does not merely track the pregenerated optimal heading reference throughout but regenerates and follows new ones whenever necessary. In other words, the vehicle follows the optimal heading references revised repeatedly on the basis of our suboptimal strategy. In this example, we set *da*, the acceptable limit of position deviation, to be 12,500 m. As noted in the figure, optimal vehicle routing is revised five times, making the vehicle to reach the destination, at last. Repeating the vehicle rerouting five times, our suboptimal guidance has succeeded in taking the vehicle to the destination. Traveling times of vehicle routings are summarized in **Table 1**. It is noted here that, while the results of vehicle routing by PN, straight-line tracking, and optimal guidance are deterministic, the result by suboptimal guidance is not since it is derived using the model including environmental uncertainties. Therefore, care should be taken in interpreting the suboptimal result. The result of suboptimal vehicle routing is event-dependent, so that it differs in every event. In **Table 1**, we find that the traveling time of suboptimal vehicle routing is 208372.0 s. Notably, it is even shorter than that of the

**Figure 15.** *Vehicle trajectories in NW Pacific generated by suboptimal routing.*

*Reconfigurable Minimum-Time Autonomous Marine Vehicle Guidance in Variable Sea Currents DOI: http://dx.doi.org/10.5772/intechopen.92013*


## **Table 1.**

*Traveling times of vehicle routings in NW Pacific.*

optimal routing in the sea current without uncertainty. This implies that in total, the uncertainties have affected the travel in a favorable manner, which may not be the case in other events, however.
