**Shuai Liu 1, Chenxu Wang 1,\* and Anmin Zhang 1,2,\***


Received: 30 June 2019; Accepted: 31 July 2019; Published: 7 August 2019

**Abstract:** The depth of water is of great significance to the safe navigation of unmanned surface vehicles (USV)in shallow waters, such as islands and reefs. How to consider the influence of depth on the safety of USV navigation and path planning is relatively rare. Under the condition of ocean disturbance, the hydrodynamic characteristics of unmanned surface vehicles will affect its draft and depth safety. In this paper, the hydrodynamic model of unmanned surface vehicles is analyzed, and a water depth risk level A\* algorithm (WDRLA\*) is proposed. According to the depth point of the electronic navigation chart (ENC), the gridding depth can be obtained by spline function interpolation. The WDRLA\* algorithm is applied to plan the path, which takes hydrodynamic characteristics and navigation errors into account. It is compared with the traditional A\* shortest path and safest path. The simulation results show that the WDRLA\* algorithm can reduce the depth hazard of the shortest path and ensure the safety of navigation.

**Keywords:** unmanned surface vehicles; path planning; hydrodynamics; electronic navigation chart; numerical simulation; water depth risk
