S/V, M/V, R/V etc.
The terms sailing vesel, motor vessel, research vessel etc. are used so that someone else can find you in a crowd by narrowing down the visual search. If you hail a bridge for opening and use S/V, the bridge tender will be looking for a sailboat and not a power boat. When the term research vessel is used, i would think about restricted ability to maneuver. Maybe pulling seismic cables, or have divers down. Its all just a quickee ID thing. Tony B