Mr. Mayor, you’re gonna need a bigger boat.

When New York City took over ferry routes along the East River, using a new fleet of small boats, and lowering the fares, officials anticipated that weekend demand might be higher in the summer.

But the city underestimated just how much demand would outstrip supply, forcing it to charter two extra boats — each capable of carrying 400 people — to handle summer weekend crowds, at a cost of $485,000 for the summer, or about $60,000 per weekend.

City officials and the contractor operating the service, Hornblower, also decided to change an existing order for new boats. The original order called for 20 boats from two shipyards on the Gulf Coast, each of which can hold 149 passengers. Now the city has asked that three of the 20 boats be larger, outfitted with bigger engines and with a capacity to hold 250 passengers, officials said on Wednesday. Those boats would not be ready until next year.