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A commercial vessel is defined by the U.S. Coast Guard as any vessel engaged in commercial trade or that carries passengers for hire. This would exclude pleasure craft or warships. Commercial vessels come in a myriad of sizes and shapes from twenty-foot inflatable dive boats in Hawaii, to 5,000 passenger vessels on the Mississippi River, to 1,000 foot oil tankers and container ships at major ports, to a passenger carrying submarine in the U.S. Virgin Islands.

Passenger vessels

A passenger ship is a ship whose primary function is to carry passengers. The category does not include cargo vessels which have accommodations for limited numbers of passengers, such as the ubiquitous twelve-passenger freighters once common on the seas in which the transport of passengers is secondary to the carriage of freight. The type does however include many classes of ships which are designed to transport substantial numbers of passengers as well as freight. Indeed, until recently virtually all ocean liners were able to transport mail, package freight and express, and other cargo in addition to passenger luggage, and were equipped with cargo holds and derricks, kingposts, or other cargo-handling gear for that purpose. Only in more recent ocean liners and in virtually all cruise ships has this cargo capacity been suppressed.

While typically passenger ships are part of the merchant marine, passenger ships have also been used as troopships and often are commissioned as naval ships when used as for that purpose.

More about passenger vessels.

Dive boats

A dive boat is a boat that scuba divers use to reach a diving site which they could not reach by swimming from land.

Features that make a boat suitable for use by divers are:

• easy and safe entry to and exit from the water
• marine VHF radio
• oxygen first aid
• diving shot

For larger boats these facilities may also be present:

• diving air compressor
• gas blending
• recompression chamber

More about dive boats.

Tankers

A tanker is a ship designed to transport liquids in bulk. Tankers can range in size from several hundred tons, designed for servicing small harbours and coastal settlements, to several hundred thousand tons, with these being designed for long-range haulage. A wide range of products are carried by tankers, including:

• hydrocarbon products such as oil, LPG, and LNG.
• chemicals, such as ammonia, chlorine, and styrene monomer.
• fresh water.

Different products require different handling and transport, thus special types of tankers have been built, such as "chemical tankers" and "oil tankers". "LNG carriers" as they are typically known, are a relatively rare tanker designed to carry liquefied natural gas.

Among oil tankers, supertankers were designed for carrying oil around the Horn of Africa from the Middle East; the supertanker Knock Nevis being the largest vessel in the world.

Apart from pipeline transport, supertankers are the only method for transporting large quantities of oil, although such tankers have caused large environmental disasters when sinking close to coastal regions, causing oil spills. See Exxon Valdez, Braer, Prestige, Torrey Canyon, Erika, for examples of tankers that have caused oil spills.

Tankers used for liquid fuels are classified according to their capacity.

• VLCC stands for "Very Large Crude Carrier", typically measuring between 200,000 dwt tons and 320,000 dwt tons.
• ULCC stands for "Ultra Large Crude Carrier", typically measuring over 320,000 dwt tons.

The following designations are not exclusive to tankers and are applied to a broad range of cargo vessels, however some were developed initially for tankers.

• Suezmax - a vessel that can transit the Suez Canal, typically measuring 120,000 - 200,000 deadweight.
• Aframax - an acronym for the Average Freight Rate Assesment, with vessels typically measuring 80,000 - 120,000 deadweight.
• Panamax - a vessel that can transit the Panama Canal, typically measuring 50,000 - 79,000 deadweight.
• MR - an abbreviation for "Medium Range", typically measuring 38,000 - 50,000 deadweight.
• GP - an abbreviation for "General Purpose", typically measuring less than 38,000 deadweight.

There are also additional designation systems used, using the "Large Range" acronyms LR, LR1, LR2, and LRC.