## 1 Introduction  
The shipping industry has achieved continuous development over recent decades due to developing technology and increasing worldwide commercial activities. Waterborne transportation is growing denser, especially in major navigation lanes and active waters such as bays, ports, inland rivers, etc. [1]. The busier the waterway, the higher the probability that more than two ships will get into an encounter situation. A multi-ship encounter situation is obviously more complex, as each ship should consider more than one target ship to make a workable collision avoidance (CA) decision. The ship CA process differs from railway and road traffic due to the significant inertia and under-actuated characteristics of ships. The inertia of ships means that emergency maneuvers during CA are affected and may not achieve the desired outcome. Under-actuated characteristics require advanced maneuver planning and the accumulation of time to achieve the desired state. Communication plays a vital role in the CA process, where ships share general intentions rather than detailed decisions. Misunderstandings in communication often lead to ship collision accidents. Research has shown that communication failure is a major cause of such accidents. The ship CA process is characterized by slow-motion changes, multiple CA communications, and highly coupled decision-making between ships. The internal and external logical structures of ship CA include observable maneuvers and hidden intentions. Through repeated communication and influencing each other's decision-making, ships can successfully avoid collisions. Traditional ship CA research is mainly based on the ship's own understanding of the current navigation state and a series of intelligent decisions from some traditional CA algorithms. Traditional ship collision avoidance algorithms primarily emphasize the geometric relationships between vessels, employing a decision-making process akin to enumeration rather than employing more sophisticated path-planning algorithms [2]. In the traditional CA scenario, the ship's CA decision often has to go through several stages: risk discovery, initial CA decision of the ship, CA decision communication between the meeting ships (usually through very high frequency, VHF), and final CA decision. Due to the huge inertia of the ship and its slow-moving speed, a CA process may take several minutes to tens of minutes [3;4]. In this process, the ships will encounter the above-mentioned communication process many times, forming a complex negotiation avoidance situation that affects both of them. This has created an industry practice in the daily navigation of ships [4]. At the same time, after studying a large number of ship collisions [5;6], it can be found that ship collisions are often caused by the failure to communicate or understand each other's intentions. Even in two-ship encounter scenarios, the above situation happens from time to time. In a multi-ship encounter scenario, if such inefficient and lengthy communication is still adopted, the possibility of collision due to failure in ship decision-making will increase significantly [7]. For the problem of communication, understanding, and trust, people naturally turn their attention to blockchain technology, especially the emergence of core technologies such as the \"consensus algorithm\", which makes it possible to achieve efficient communication of CA strategies, even between ships that are complete strangers to each other, through the blockchain formed temporarily. Another major idea to solve the navigational safety problem is intelligent ship decision-making, or a maritime autonomous surface ship (MASS) [8;9]. MASSs have formed an industry consensus, and there is a global boom in MASS development. However, intelligent decision-making systems, even with the ability to process scenarios more quickly and effectively than experienced crews [10; 11; 12], still cannot solve a core problem in the ship CA process [13]: how to handle communication and trust management between participants?