If they were searching for drugs then they should say they are searching for drugs and not claim "safety inspection."
4th Amendment: "... particularly describing the place to be searched, and the persons or things to be seized."Just tell the boat owners what they are really searching for. What's wrong with that?
Suppose for a moment these were the real mccoy smugglers. Would you advise starting the search with the statement "We suspect you of smuggling, and we are going to look for drugs", or the non-confrontational "We would like to perform a safety inspection".
These LE guys would like to see noone get hurt, including themselves.