SEATTLE — A federal investigation of why the Alaska Ranger sank in the Bering Sea after the fishing vessel lost power on Easter Sunday and then went into reverse has led the Coast Guard to issue a safety warning to ship owners about controllable-pitch propellers.

“Sitting on this for six months is against the interest of marine safety,” said Capt. Mike Rand, chairman of the Marine Board of Investigation. “That’s why we got it out right away.”

A final report on the incident aboard the Seattle-based catcher-processor boat, in which five of 47 crewmen died, is expected in about six months.

Nationwide, hundreds of seagoing vessels have controllable-pitch propulsion systems, which allow the angle of the propeller blades to be adjusted to improve efficiency and directional control.

“The Coast Guard strongly recommends that owners, operators and masters of vessels with controllable-pitch propellers understand the design and operation of the system,” the Coast Guard safety notice states.

Rand said it was difficult to figure out the correct wording for the warning, which was issued earlier this month, because it is not clear that all controllable-pitch systems will send a vessel into reverse if electric power is lost, and at what point that might happen.

The 200-foot Alaska Ranger began leaking in its stern for an undetermined reason while the boat was headed to mackerel fishing grounds off the Aleutian Islands. Eventually, the boat’s power started to flicker and the vessel started moving in reverse.

The boat’s officers decided to keep the main engine running, which would propel the boat backward, rather than shutting down the engine and leaving the vessel adrift. Once the vessel starting going in reverse, survivors said it listed sharply and appeared to be in a more precarious position.

“We started going down pretty fast after that,” said Gwen Rains, a federal fishery observer who survived the sinking.

The backward movement also made evacuating the boat more difficult. Two of three life rafts moved out of reach of the crew and most of the 47 people aboard were forced to jump into the 34-degree water.

“Ultimately, only 22 members of the vessel’s crew made it into the life rafts. Of the other 25 members who never made it into a life raft, four died and one remains missing,” the Coast Guard notice stated.

Coast Guard investigators are developing a model to simulate the effects that the reverse motion had on the vessel’s stability, Rand said.

“We hope the model will be able to explain this,” Rand said.