Currently in the design and blueprint stage, the boats will not be sisters. S.S. Alexandra will be a sister vessel to the 164-passenger S.S. Antoinette, named as a Cruise Critic Editors' Pick as the best new riverboat in 2011. Antoinette sails exclusively on the Rhine, but Alexandra will debut sailing the Rhine, Main and Danube rivers.
S.S. Catherine, on the other hand, will be fashioned after the 132-passenger River Royale. That ship, which launched in 2006, is based on France's Rhone River. S.S. Catherine will also sail exclusively in France though Uniworld declined to identify its itinerary at this point.
Both ships will be designed with Uniworld's customary elegance created by Beatrice Tollman, president and founder of Red Carnation Hotels.
Maria Grimardi, vice president of marketing for Uniworld, told Cruise Critic that both "will be reflective of the areas they are traveling, so they will be very unique."
"None of our ships are designed and styled the same," she explained.
Uniworld isn't the only river cruise operator with newbuilds on order or recently delivered. With the popularity of river cruising exploding, just about every major line has ships that are newly launched, under construction or waiting to be built.
Avalon Waterways took delivery of two new boats this year and will launch its twelfth and thirteenth European riverboats, Avalon Artistry II and Avalon Expression, in 2013.
AMAWATERWAYS took delivery of AmaCerto this year, and will launch AmaPrima and AmaVida next year.
But the award for the most robust expansion goes to Viking River Cruises, which is taking delivery of a record six new Longship-class boats this year -- Viking Aegir, Viking Embla, Viking Freya, Viking Idun, Viking Njord and Viking Odin. Next year the line repeats the feat, with six more Longships set to launch.
In other newbuild news, Viking River Cruises is expanding beyond Europe's in-land waterways, making its first foray into ocean cruising. Viking Ocean Cruises, a newly formed sister company, says it has signed a contract with Italy's Fincantieri for the construction of two ocean-going vessels. Each ship will feature 474 cabins and measure 47,000 gross tons. The first is scheduled for delivery in early 2015, while the second will launch in 2016.
--by Dori Saltzman, News Editor