Honolulu's plan for a new commuter ferry system sailed into rough water yesterday but appeared to remain afloat for now.

Mayor Mufi Hannemann hopes to launch daily ferry service from Kalaeloa to Aloha Tower in July, but City Council members sharply questioned the plan yesterday and indicated they may withhold final approval.

The plan for three daily trips in each direction does not appear likely to attract many commuters who don't already ride city buses, so the $6 million annual cost might not be justified, Councilman Donovan Dela Cruz said.

Council transportation chairman Nestor Garcia and others also said they were not convinced the plan is well-conceived.

It calls for ferries that would carry up to 149 passengers and make three trips per weekday in each direction, for a total daily passenger count of 447 each way.

The city expects to pay for the ferries with a $5 million federal grant, and to spend $1 million more for a system of shuttle buses to bring passengers to and from each terminal.

But the Federal Transit Administration has yet to approve the plan and release the grant money, ferry project manager Darin Mar said.

Potential ferries have been identified but have not been leased, and an initial 6-month contract with Hornblower Marine Services has not been finalized, he said.

An attempt to secure parking for ferry passengers at a Kapolei mall fell through, but the city still hopes to find parking elsewhere, he said.

A single city bus fare — adults pay $2 for a one-way trip — would be charged for the ferry and bus rides at each end. Monthly and annual bus passes also would be honored on the ferry.

But Councilman Rod Tam said the city should see whether a private bus operator could run the shuttles at a lower cost than the $1 million the city expects to spend.

And Councilwoman Ann Kobayashi said it might not be prudent to pay for ferry service without any guaranteed minimum ridership.

The system would be the third attempt in recent years to link Leeward O'ahu with downtown Honolulu by ferry. Earlier efforts suffered from low ridership and ended when federal grants ran out.

But officials say this system would be better because it would include the dedicated shuttle bus lines, serving Wai'anae, Makakilo, Kapolei, Waikiki and the University of Hawai'i-Manoa.

Hornblower also expects to launch the interisland Hawai'i Superferry in July, with service from O'ahu to Maui and Kaua'i on a ship that can carry cars as well as passengers.

Reach Johnny Brannon at jbrannon@honoluluadvertiser.com.