Officials said it was not immediately known why three other people on the sailboat waited so long to try get help for the two in the water.
Lt. Sue Stangl of the Seattle Fire Department said authorities received an emergency call at about 3:35 a.m. and launched a water rescue that also involved resources of the Seattle police, the Coast Guard and the King County Sheriff's office.
She said it appears one of the people on the 40-foot sailboat went into the water, and the second person went in to help the first one. The second person was unable to help and became stranded overboard, too. All the pair could do was cling to the side of the boat and wait for assistance.
The three other people on board the vessel threw ropes and life jackets to the two in the water, said Seattle police spokeswoman Renee Witt, but apparently were unable to help them get back on board the boat. Finally someone called 911.
"My understanding is that they were in the water for approximately 45 minutes until we were notified," Stangl said. "And in this kind of temperature that is pretty significant. It does not really allow you to have that strength to hold on."
She said the life jackets probably saved their lives.
"In this situation that definitely did make a difference," she said.
Emergency responders reached the scene and were able to get the two people inside a harbor patrol boat. They were taken to shore, then to Harborview Medical Center for treatment of hypothermia. Both were expected to survive.
After the rescue, a Coast Guard vessel escorted the sailboat and the three other occupants back to Shilshole Bay Marina.