33 CFR 95.020 – Standard for under the influence of alcohol or a dangerous drug
An individual is under the influence of alcohol or a dangerous drug when:
(a) The individual is operating a recreational vessel and has a Blood Alcohol Concentration (BAC) level of .08 percent or more, by weight, in their blood;
(b) The individual is operating a vessel other than a recreational vessel and has an alcohol concentration of .04 percent by weight or more in their blood; or,
(c) The individual is operating any vessel and the effect of the intoxicant(s) consumed by the individual on the person’s manner, disposition, speech, muscular movement, general appearance or behavior is apparent by observation.