Welcome to the Shaft Alley!
Image of shaft alley showing screw shaft and carrier bearing. Note the shaft continuing into the background
Shaft alley is the long, narrow passage way where the screw shaft runs from the output of the turbine reduction gears to where the tail shaft exits the ship and connects to the screw. The 166 ' long shaft is comprised of several segments joined by pins allowing for the removal of a segment in the event that a bearing needs inspected or replaced. Each shaft segment has a 16" diameter except for the flanges where each segment is joined together. The shaft rests on lignum vitae carrier bearings. There is one carrier bearing at each shaft segment joint. At full power, the shaft transmits up to 6000 hp. from the reduction gears to the ship's screw at 90 revolutions per minute.
As part of his watch, the oiler is responsible for periodically checking each shaft-carrier bearing to ensure it is adequately lubricated and not overheating. The oiler is also responsible for checking the rear-gland seal where the tail shaft exits the ship to ensure no sea water is leaking through. It is not uncommon for the oiler to make their rounds of shaft alley frequently during watch since the alley offers a respite from the 120 degree heat of the engine room.
The following series of photographs show the rear-most shaft segment removed during the our 2004 dry-dock so that the tail shaft could be pulled and inspected. (photos courtesy of Chris Brooks)
Rear shaft segment removed. Note the rigging in place to hold the shaft and the size of the shaft pin holes in the flange.
Tail shaft rigging to support and pull tail shaft for inspection
Image showing tail shaft pulled and ready for inspection