The Canadian Coast Guard has been forced to spend more than $2.5 million this fall to charter vessels to carry out at-sea science surveys because a much-delayed refit has left its own research ship unavailable.

Canada's East Coast ocean monitoring program usually takes place on the CCGS Hudson, but the 54-year old vessel is still not ready after a $4-million refit ran six months behind schedule.

In place of the Hudson, the coast guard has been forced to charter three private vessels at a cost of $2.58 million, excluding tax, CBC News has learned.

"Requests for proposals processes were conducted to secure alternative vessels for three zones which have been surveyed every year since 1998," Department of Fisheries and Oceans spokesperson Vance Chow said in a response to CBC News questions about the fallout from the refit.

Vital information on ocean health

The twice-annual surveys collect a wide range of physical, chemical and biological data to measure ocean conditions.

The information helps scientists understand ocean health and in recent years provided evidence of a dramatic rise in sea temperatures around Atlantic Canada.

The RV Coriolis will carry out the 30-day survey in Gulf of St. Lawrence at a cost of $721,568. The University of Rhode Island is supplying the RV Endeavor for the Maritime program at $1,041,044, and the Dutch multinational Fugro is supplying the MV Discovery at $822,000 for monitoring off Newfoundland and Labrador.

As for the Hudson, it returned to its home port in Halifax one week ago, with the refit still unfinished.

"There is some minor outstanding work required that will be conducted alongside the ship's home port at the Bedford Institute of Oceanography," Chow said.

Lloyd's Register, the U.K.-based marine safety certifier, has given the vessel an interim provisional certificate, which is valid until Jan. 31, 2018.

The refit of the vessel was supposed to be finished by last May. (DFO Maritimes/Twitter)

The dry dock maintenance at Heddle Marine in Hamilton, Ont., was supposed to be completed last May.

In October, the federal government lost patience and towed the Hudson out of Heddle Marine, fearing the refit would not be finished before the St. Lawrence Seaway closes for the winter at the end of December.

The coast guard has not said why the refit was delayed or what work remained when it yanked the ship out of the yard.

Planned modifications to cabins and laboratories on board the Hudson will be carried out in January at the Bedford Institute of Oceanography in Dartmouth, N.S.

The coast guard now says the Hudson will be back in service in April 2018.