In some cases a towing vessel and her tow, a fishing boat, and a vessel at anchor have a priority against a general power-driven vessel underway in the application of collision rule. This article aims at suggesting a practical guide for the construction of the meaning of a vessel engaging in fishing, a vessel engaged in towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course and a vessel at anchor, which are permitted to have the above priority. The construction of the application of the collision rule on the above vessels is supported by the decisions of MAIA and the judgment of civil courts.