Hypothermia can a kill anyone working away from shore in cold weather. You have little chance of survival if you fall overboard or have to abandon a sinking ship.
Immersion suits (aka survival suits) can significantly improve survival time in cold water. Recognizing that hypothermia is a major factor in lives lost at sea, the U.S. Coast Guard now requires immersion suits on documented vessels operating north of 32 degrees North and seaward of the Coastal Boundary Line. Immersion Suits are an important piece of life saving equipment.