It seems like the gCapt knowledge pool on slow speeds is much shallower than I realized. I’ve been working slow speeds since 2007 with a 5 year hiatus into the world of medium speeds that ended almost 10 years ago. I’m just shy of a decade as a senior engineering officer. Based off of the ships I’ve been on, I’m comfortable making some generalizations with the caveat that there are always going to be the outlier ships that I haven’t experienced that don’t go with the generalizations.
While I’ve never been on the Dali and don’t know the exact arrangement of the machinery space I can speak some on the common designs and setups of shipboard engine rooms. Power generation in the engine room can be broken into two main components: Electrical generation and Propulsion. On a ship such as the Dali there will be several generators powered by medium speed diesel engines for electrical generation and typically one slow speed to provide propulsion.
The electrical system is commonly broken into the Main Bus and Emergency Bus. The Main Bus is the majority of machinery on the ship. The Emergency Bus will power critical machinery but is not necessarily set up to preserve propulsion. Under normal operation, all power for the Main Bus and Emergency Bus will come from the ship’s generators. The generators are typically sized so that the full ship’s load can be carried with one or two generators, with additional generators available for extra consumers. On a container ship, these extra consumers may be ventilation fans, refrigerated containers or thrusters. While maneuvering the ship into or out of port, I want to have at least one more generator online than I need. This provides a buffer in the event that a generator fails as there’s already a generator online and running that can shoulder the load and reduce the risk of a blackout.
There is a smaller Emergency Diesel Generator (EDG) on board. In the event that a blackout occurs, the EDG is supposed to automatically start and provide power to the Emergency Bus. It’s not a big generator and you aren’t going to be able to run larger pumps with it. You will have the ability to use a fire pump, a steering gear pump, emergency lights, automation and wheelhouse electronics and various other small consumers. It’s meant to be an emergency backup that allows us to fight a fire, continue steering or bring the ship back from a blackout. I can walk onto any ship with a functional EDG, start it off of battery power or a hydraulic hand pump and get the ship to the point to where I can start one of the larger generators.
Separate from the electrical system will be your main propulsion. The most common setup for container ships, ROROs, bulk carriers and many tankers is a single slow speed main engine. These engines range considerably in size depending on the cylinder bore and count. The largest are pushing over 100,000hp. I’ve been working mostly on the smaller ones in the 15,000 to 20,000hp range but they’re all fundamentally similar, they just vary in the size of the components. As implied by the name, a slow speed operates at fairly low RPMs. The fastest I’ve personally seen could do 120rpm. The low speed allows for directly connecting the propeller to the main engine via a shaft and eliminates the need for a reduction gear. One quirk of the slow speed is that in order to change the ship’s direction, from ahead to astern for example, you must first stop the engine and then restart it in the opposite direction. On older engines this was done by shifting the camshaft forward or back to move onto a different set of camshaft lobes. On newer engines the camshaft has been replaced with hydraulic actuators and solenoid valves that allow for a wider range of adjustment of the engine parameters.
One issue that arises when you stop an engine is that anything driven by the engine also stops. Lube oil and cooling water pumps, for example, need to be kept running. This means that most of the ancillaries needed to actually operate the engine are not driven by the engine, they are powered from the electrical bus. This is typically the pumps needed for lubricating and hydraulic oils, the high and low temperature cooling water circuits, the fuel system and the compressors needed for the compressed air systems. I have never seen any of this equipment on the Emergency Bus, nor have I seen an EDG large enough to power all of this stuff. The gist of it is that you’re almost certainly going to lose propulsion when you blackout a slow speed propulsion plant.
So, what happens after the blackout? Well, hopefully the EDG has kicked on and your automation is still up and running (this is typically on a UPS as well as the Emergency Bus). As mentioned earlier, the EDG should have some of the basics up and running within a minute. The automation should be trying to bring the next standby generator online while the EDG is going through its start cycle. How long this takes can vary from plant to plant, machine to machine. I’ve seen engine rooms where a certain generator in standby would start and come online faster than the emergency. Once all of the lights are back on, the automation should next begin starting the essential pump motors sequentially. The goal is to bring things back online without overloading the generator by starting too much too quickly. Sometimes it works great and you can go from blackout to back up and ready to start propulsion in about a minute. Sometimes it doesn’t go great for any number of a variety of reasons. Just in my personal experience, I’ve had two blackouts caused by accidental activations of the quick closing fuel system valves (one human error, one mechanical failure). I’ve seen blackouts caused by an update in the automation, faulty overspeed devices, accidental activation of the emergency stop, hitting the stop button on the wrong generator, opening the circuit breaker on the wrong generator, improperly adjusted high temperature shutdown switch, a broken tube going to the lube oil pressure switch, faulty wiring, water in fuel, bacteria in fuel, an improperly set up governor, a plugged lube oil strainer, a plugged fuel strainer… the list can go on and on.
In the case of the Dali, we know she blacked out. If the EDG came on she should have been able to maintain steerage but it does appear that for whatever reason she continued turning to stbd. The stbd turn could also have been caused by the helmsman turning the wheel to the right instead of turning to the left (which is shockingly common). We know she was able to restore power briefly. I can’t tell if it was enough to actually get the main engine restarted. There is a large puff of smoke visible in the video but the video isn’t clear enough for me to tell if that’s coming from the main engine or generator exhaust. The lights go on, the lights go off. Are these lights on the E-bus or main bus? We don’t know but I suspect the main bus.
Was the engine room attended or unattended? I don’t know for sure in this case. Based off my experience it was most likely attended. I would have a very difficult time flipping the UMS switch and heading out while under pilotage. None of the companies I’ve worked for would permit this. As CE, it’s usually myself and the duty engineer in the engine room at a minimum. I’m usually down there from 1 hour notice until about an hour after the ship gets up to sea speed after dropping the pilot.