Hullo Ken,
Your post about having 9 engines giving maximum flexibility is very correct - most shipowners would love to have the ability to maintain schedules the way QE2 did (i.e., post the cruise itinerary 18-20 months in advance and in she comes, on the stated day, and right on time as well! Impressive). The capital cost to install the D/E system was huge, although I bet it paid for itself handsomely, many times over since. QM2 does have good schedule flexibilty,
BUT, if she loses one DG, then they have to power up a GT to maintain the schedule, and that costs a lot more than just starting another DG as QE2 would do.
Regarding present generator loadings on QE2, I would be very surprised if the DG that is running is at more than 50% output. If you run all sorts of current-hungry systems just to keep the electrical load up and the engine at a decent load factor, you have to consume more fuel, so the costs go up.
Recently I posted a control room photo that was taken (in June 2007 I think) when a notice was posted that divers were in the water. The ship had managed to get 2 mooring lines around the port screw when berthing in Southampton. The nylon line came away easily and caused no damage, while the other line was not nylon, and took more time to release. So, it was a normal pax-change day in Soton, but only one DG was running (Hotel), and obviously carrying all the normal loads.
Tied up alongside the wharf with no pax on board, the galleys, pantries, laundries, fresh water, gray water, black water, lube oil/fuel oil pumps & systems, heaters and purifiers, control & starting air compressors, firefighting precharge pumps & systems, stabilizer/ballast/trimming/steering gear pumps, machinery lubrication & cooling pumps, navigation systems loads, lighting, deck winches/windlasses, passenger and crew lifts etc, are all in hibernation. Sometimes it can be a real job to find enough load to test generating systems when a ship is virtually mothballed.
I would be surprised if the engines are still running on HFO, but who knows? Maybe Dubai are not worried about the higher emissions from the incomplete combustion of the heavier fuel being consumed at light load.
When the ship was about to put to sea, (or the present owners decide to run the shafts up), at least 3 DGs have to be running to 'swing the props', as the starting current will be very high, but once the shafts are at 72 rpm, the starting current would have dropped back. Current will then rise again as pitch was applied to the propeller blades. The load control system would then successively start more generators, to enable more pitch to be applied, until reaching the point where the shaft speeds would be doubled to 144 rpm (after actually dropping some pitch off first), and then even more pitch would be applied until the desired speed was achieved. The main machinery will be suffering from all this lack of use, and no doubt unforeseen problems of various kinds will appear when someone tries to take her back to sea again. A ship is happiest when it is at sea
- that goes for the machinery and systems, as well as (most) of the crew and passengers!
Cheers
Skilly
