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allision When two vessels underway run into each other it is called a collision. When a vessel runs into a dock (assumed above the water) then that is an allision. Allision is damage causing impact between a vessel underway and something not moving, such as an anchored vessel. This would seem just Admiralty Court jargon—there is, for example, an official “Oregon Rule” that presumes the fault lies with the moving vessel—but there are more subtle implications to this concept that I have always considered fundamental to basic navigation. The word allision is not in the Navigation Rules. In fact, the only reference in the Rules at all that refers to collisions with anything other than another vessel is in Rule 6 (b) ii, on the things we must take into account when choosing a safe speed when using radar: “the possibility that small vessels, ice and other floating objects may not be detected by radar at an adequate range.” [emphasis added]. Though never stated specifically, clearly the authors of the Rules intended this document to be the guide to not running into anything. And it remains true. If you know and obey the Rules, you will avoid not just collisions but also allisions and minimize chances of running aground. See also Tricky Terms in Navigation.

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