|HMCS TORONTO in January 2015, returning from her last deployment prior to her mid-life refit.|
The propulsion plant of the HALIFAX class represents somewhat of a departure from earlier RCN surface warships. The three earlier classes (Tribal, St. Laurent family, & IROQUOIS) were fitted with two pairs of steam or gas turbines, for cruise and boost power (though in the case of the ST. LAURENT class, they were designed with cruise turbines that were either later removed or not fitted at all to later ships of the class). The HALIFAX class, while retaining two gas turbines for high speed, uses a single diesel engine for fuel efficient operation at cruising speeds. They also have a unique gearbox arrangement to allow a CODOG (Combined Diesel or Gas) arrangement. I believe these ships were the first RCN warships to use diesel propulsion since a batch of BANGOR class minesweepers commissioned during the Second World War.
Also unlike previous ships, the cruise and boost powerplants are installed in separate compartments. The propulsion diesel is situated in the aft engine room, and the gas turbines are fitted in the forward (and larger) engine room along with three gearboxes.
While I was doing my tour, the diesel propulsion engine was actually being dismantled piece by piece and removed through a hole in the deck.
|Looking down into the aft engine room.|
|Looking down into the aft engine room, but from one deck lower.|
A series of "soft patches" in the various decks above the engine room can be removed to allow the removal of engine components. We were there just in time to see one of the turbo-chargers being lifted out. In contrast, I believe the gas turbines can actually be removed more or less in one piece, up through the funnel - thought it requires disassembly of the enclosures and trunking. This has allowed gas turbines to be replaced in foreign ports during the extended deployment of some ships.
|Turbo-charger being removed by FMF Cape Scott personnel. A turbine on the exhaust stream powers a compressor that increases the amount of combustion air in the diesel's 20 cylinders, allowing the engine to produce more power.|
As I recall, SEMT-Pielstick (recently rebranded as MAN Diesel) designed the 20-cylinder, 8,800 shp, propulsion diesel specifically for this class of ship - I don't know if it has been used anywhere else. This led to some teething issues early in the life of the class. The engine is normally hidden inside an enclosure, but during my visit the enclosure was opened up and the engine partly torn down. (Clarification: the engine block itself was not removed, but the engine was stripped down prior to the refit.)
|Partly torn down Pielstick diesel inside its enclosure. To the left of the photo is the forward bulkhead.|
The diesel's drive shaft leaves the engine and heads to the forward engine room, where it intersects with the centreline of the ship's Royal Schelde cross connect gearbox. The cross connect gearbox allows the single diesel to drive both propellers.
|Looking forward in the forward engine room. The Royal Schelde cross-connect gearbox is in the immediate foreground, while the port and starboard gearboxes and gas turbines are partly hidden behind piping.|
- diesel engine driving either or both shafts
- port gas turbine driving either or both shafts
- starboard gas turbine driving either or both shafts
- both gas turbines driving both shafts simultaneously.
In a CODOG powerplant, propulsion diesel and gas turbines can not power the propellers at the same time.
|Port gearbox looking forward.|
|Starboard gearbox looking forward, with the back end of the gas turbine enclosure visible.|
- If the diesel engine fails, either or both gas turbines can be used for propulsion.
- If either gas turbine fails, either the diesel or the remaining gas turbine can provide propulsion.
- If the cross connect gearbox fails, the gas turbines can be used through the port and starboard gearboxes (although they are dedicated to a single propeller shaft).
- If either or both port and starboard gearboxes fail, the diesel engine can still work through the cross-connect gearbox, or a remaining gas turbine can work through its gearbox.
- If either propeller or shaft experiences problems, power can be routed to the remaining shaft.
|Looking forward, the starboard propeller shaft leaving the cross-connect gearbox.|
|Port propeller shaft leaving the cross-connect gearbox. When the ship pulls into port, and stops her engines, the ship's company holds a 50/50 lottery on which number each shaft will stop on, with part of the proceeds going to charity.|
|Port propeller shaft looking aft.|
|Looking aft between the two gas turbine enclosures. The two doors visible access the interior of the enclosures.|
|Looking through a window in the enclosure at the compressor stages of the starboard LM2500 gas turbine.|
|Looking to starboard along the catwalk at the aft end of the forward engine room, with the local control panel to the right.|
|Head-on photo of the local control panel.|
As with the previous IROQUOIS class, the HALIFAX class has two controllable pitch (CP) propellers. The propeller blades can be controlled to provide different degrees of forward or reverse thrust. The engines, and in particular the gas turbines, generally have speeds at which they are more efficient than others. The propellers allow the engines to be kept within their most efficient operating parameters, by controlling the propeller pitch rather than the engine speed. The CP props are also useful in transitioning to reverse thrust - gas turbines only spin in one direction.
Although many systems are being replaced as part of the mid-life FELEX refit, the engines and gearboxes shown here will continue to propel these ships into the third decade of this century.