Honolulu's intra-island commuter ferry service has been running at full strength for more than a month and yesterday carried its 20,000 passenger.

"We are pleased that many residents continue to use 'The Boat' as a transportation alternative," Mayor Mufi Hannemann said in a news release.

The twin 72-foot aluminum catamarans Rachel Marie and Melissa Anne began running Kalaeloa-to-Honolulu routes in September. Each vessel seats 149.

"Despite some trouble with one of the engines on the Rachel Marie late last year, TheBoat has basically been running strong every day Monday through Friday, with two ferries providing three trips into Aloha Tower from Kalaeloa in the morning, and three trips back in the afternoon," said Wayne Yoshioka, city director of transportation services.

A one-way trip costs $2 for adults. Bus passes are also honored.

The ferry service and five linked bus routes are expected to cost $6 million a year. Federal grants are providing $5 million.

Hannemann has characterized the ferries as an important alternative to driving on the island's crowded roads and freeways.

"Based on surveys we've been conducting with passengers and other input, we will soon be looking at the possibility of adjusting TheBoat's schedules in order to better serve our customers," Yoshioka said.

Reach Peter Boylan at pboylan@honoluluadvertiser.com.