## 5 Conclusions  
This paper proposed a novel low-latency and energy-efficient opportunistic routing protocol to achieve timely and accurate data delivery in MSR-WSNs. Link connectivity among marine nodes, integrated with geographic progress threshold are explicitly considered when selecting candidate nodes for data packet forwarding. Moreover, the optimal expected packet advancement and the minimum waiting-time \(t_{\text{min}}\) are utilized to minimize time delay. Subsequently, the priority \(P_{ij}(t)\) of candidate nodes is calculated and sorted in descending order. Eventually, the packet forwarding is completed using timer-based coordination algorithm. Our simulation results validated that the proposed opportunistic routing protocol performs better than the benchmark algorithms in terms of three metrics: data packet delivery ratio (increased by more than 21.4%), time delay (reduced by more than 39.2%) and energy consumption (decreased by more than 18.1% at average node speed is 20 m/s). The work of this paper is expected to greatly improve the efficiency and success rate of maritime search and rescue while reducing the time delay. In the future, we will conduct the actual marine experiments (ship detection [32]) to test the engineering applicability of the proposed opportunistic routing algorithm. Meanwhile, combining the power control mechanism and the existing marine sensor networks localization algorithm [33; 34; 35; 36] to assist opportunistic routing design is also one of the directions worth studying. In addition, there is a lack of research on underwater sensor networks in this paper, and how to design an opportunistic routing protocol for heterogeneous underwater sensor networks to achieve reliable high-speed transmission of underwater data is another potential research direction.  
Figure 8: Comparison with variable \(\sigma^{2}\). (**a**) Packet delivery ratio. (**b**) Average energy consumption of nodes.  
**Author Contributions:** [PERSON] proposed the main ideas, wrote the paper, designed the description framework, and conducted the simulations. [PERSON] and [PERSON] provided guidance for the work and acquired funding. [PERSON] and [PERSON] provided guidance for the work, reviewed the paper, and collaborated in discussion on the proposed system model and opportunistic routing protocol. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This study is supported by the National Natural Science Foundation of China (Nos. 52201403, 52201401, 52071200, 52102397), the National Key Research and Development Program (No. 2021 YFC2801002), the China Postdoctoral Science Foundation (Nos. 2021M700790, 2022M712027), the Fund of National Engineering Research Center for Water Transport Safety (No. A2022003), the Foundation for Jiangsu key Laboratory of Traffic and Transportation Security (No. TTS2021-05), the Fund of Hubei Key Laboratory of Inland Shipping Technology (No. NHHY2021002).  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The authors want to thank the anonymous reviewers for their time towards the manuscript.  
**Conflicts of Interest:** The authors declare no conflict of interest.