Thought the same thing so I googled "manifestly unsafe voyage":

https://www.law.cornell.edu/cfr/text/33/177.07

(f) Designated manifestly unsafe for a specific voyage on a specific body of water due to:

(1) Unsuitable design or configuration, or

(2) Improper construction or inadequate material condition, or

(3) Improper or inadequate operational or safety equipment, and set forth in an order issued by a District Commander according to the provisions of § 177.04.