It is a real stretch of the COLREGS to need a watch on a boat this size at a marina or in a designated mooring area. Properly securing your boat is obvious here. I would enjoy seeing a rule or case law that my personal boat properly secured in its marina needs a watch. Although the COLREGS rule quoted above (#5) doesn't specify "underway" I don't think it applies to a marina situation.
A vessel in a mooring area according to COLREGS is not a vessel "not under command". I guess technically when it left its mooring for a joy ride it could be considered NUC.
In fact because the boat this size is in a designated mooring area/anchor area it actually doesn't need any lighting. In practice I have many lights lit at night in the BVI when moored or anchored regardless of location.
And I do have an anchor watch on at all times when moored or anchored
All IMHO
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