It's a drug and you're in or operating a vehicle I'd say it's no different than having an open bottle of alcohol.

Police in my province have been trained to spot DUI of drugs (besides alcohol) mostly pot since it seems many people think it's OK to drive stoned.

Having an open bottle of alcohol and drinking it is legal on a boat. You just can't be intoxicated.

The USCG has several sets of classes of ships, informally known as black, white and red hull. Black does what you say, white does border patrol for drugs and people illegally entering the country, and red is scientific and icebreaking. See http://www.uscg.mil/proceedings/spring2011/articles/10_Tlapa...

In the Gulf of Mexico and the area around Florida, the Coast Guard does an enormous amount of drug-traffic-policing.

Looks like there's a wide swathe of "homeland security" missions on top of the more traditional missions I was aware of, deemed "non-homeland security":

http://en.wikipedia.org/wiki/United_States_Coast_Guard#Missi...

I wonder how this all interacts with the CBP.

Around here, Southern California, the Coast Guard regularly does drug interdiction duty. The boating safety stuff is usually done by the Harbor Patrol/Sheriff's Department.

US Coast Guard patrols down here in Costa Rica all the time specifically hunting for drugs.

The Coast Guard has a very interesting set of law enforcement, military, and regulatory authorities.