Ferry vs. transbordeur vs. traversier vs. bac

The French language has several words to describe different types of vessels used to transport people, vehicles and goods across bodies of water. These include 'ferry', 'transbordeur', 'traversier' and 'bac'. Although these terms can be used interchangeably to a certain extent, they each have nuances of usage depending on the context and region.

Ferry

A generic term borrowed from English, commonly used in France to refer to a large ship designed to carry passengers and often vehicles across significant bodies of water like seas or large lakes.
Nous avons pris le ferry pour traverser la Manche et aller en Angleterre.
(We took the ferry to cross the English Channel and go to England.)

Transbordeur

Historically, this word refers to a type of ferry that includes a movable segment such as a gondola or platform that transports vehicles and passengers over a shorter distance, often where there is no bridge. The term is also used for transporter bridges where a movable platform is suspended from a metal frame.
Le transbordeur de Rochefort est l'un des derniers ponts transbordeurs en France.
(The Rochefort transporter bridge is one of the last transporter bridges in France.)

Traversier

This term is mostly used in Canadian French, particularly in Quebec, for boats or ships that ferry passengers and vehicles across rivers or between islands and the mainland. It's similar to 'ferry' but is specific to that region's dialect.
Le traversier qui relie Québec à Lévis est très fréquenté.
(The ferry connecting Quebec City to Levis is very busy.)

Bac

Refers to a flat-bottomed boat or float used in a river or canal crossing for transporting goods and/or vehicles. Bacs are typically associated with shorter crossings and are often operated by cables or guided along chains. This term also harks back to simpler or more traditional types of ferries.
Pour traverser la rivière, nous avons pris un bac qui pouvait accueillir deux voitures à la fois.
(To cross the river, we took a ferry that could accommodate two cars at a time.)
Les agriculteurs utilisent le bac pour amener leurs produits au marché de l'autre côté du fleuve.
(Farmers use the ferryboat to take their products to the market on the other side of the river.)

Summary

In summary, while all four terms can be applied to ferries, 'ferry' tends to refer to larger sea-going vessels, 'transbordeur' usually refers to either a transport bridge or a gondola ferry system, 'traversier' is more regionally specific to Canada and is generally applied to river ferries, and 'bac' tends to refer to simpler or traditional flat-bottomed river ferries, often found in rural areas or for short crossings. Each term has its own connotations based on size, technology and geography within the Francophone world.