There are at least three public (e.g. free) portals to the USCG Documentation database for vessels.
Query by vessel name: NOAA National Marine Fisheries 
Query by vessel Official Number: NOAA National Marine Fisheries 
Limited wildcard field searchs: USCG POSIX (Port State Information eXchange) 
There is at least one commercial website that sells access to the monthly data distribution from the US Coast Guard. The site is targeted primarily for sales or marketing purposes. Online tools to sort, extract, generate labels, and the like are provided with the subscription cost.
A one-time shipment or a monthly CDROM subscription to the data is available through the US Government Printing Office as well. Only the raw data is shipped, there are no access or search tools provided.
The USCG National Vessel Documentation Center can be found online here .