When Trailer Bridge Inc. launches its maiden Jacksonville-San Juan voyage Thursday, it will broaden the pallet of shipping services to the Caribbean island, a company official said.

Paul T. Conboy, vice president of administration, said Trailer Bridge's use of 48-foot highway containers will offer customers at either end a convenience the three companies which currently dominate U.S.-Puerto Rico trade do not provide."The 48-foot trailer is a recent addition to the U.S. market. Ships in the Puerto Rico service were built prior to the introduction of 48-foot trailers, so ships that call on San Juan aren't outfitted to handle trailers," Mr. Conboy said in an interview.

"It takes a great deal of capital (to change over), and they haven't done it because they don't want to mix their equipment with the new configuration. They'd have to take their ships out of service. We're not in business yet, so we have that luxury."

Trailer Bridge will use two triple-deck barges, each with a capacity of 266 trailers. Mr. Conboy said shipping by barge can represent a savings of up to 25 percent over conventional shipping methods.

Still, the company faces some formidable odds in cracking the Puerto Rican market, compounded by excess shipping capacity and the U.S. recession.

The 8-month-old company's makeshift, second-floor office in San Juan's upscale Metro Office Park is literally right down the street from the gleaming, new headquarters of its toughest competitor, the Puerto Rico Maritime Shipping Authority.

Navieras, as the government-owned line is known in Spanish, has captured half of the U.S.-Puerto Rico shipping trade, estimated at $700 million annually, with smaller market shares divided among Crowley Maritime Corp.'s Trailer Marine Transport, Sea-Land Service Inc. and a much smaller carrier, Marine Transportation Sea-Barge Group Inc.

Trailer Bridge hopes to get a small piece of that pie, though Mr. Conboy concedes that "we're never going to be large."

The five-day service between Jacksonville and San Juan is most suited for shipment of consumer products, canned food, furniture and other items that do not have to arrive at their destinations immediately, he said.