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Because it’s cheap.
Here’s site with a chart at the bottom showing gas, diesel and heavy fuel oil prices from 1992 to 2011. The hevay stuff looks about 20% cheaper throughout.
Ahhh, not exactly sure what you mean. Whether they have giant diesel engines or oil-fired steam turbines, they’re burning very similar grades of oil. From the early 1900s until the last twenty years or so they were oil burning steam turbines because they were simpler & less expensive to build & maintain & operate. In the last few decades giant diesel engines, though more complicated, have become viable (i.e. more efficient). But like I said there isn’t too much difference between diesel fuel and bunker fuel…
I was under the impression that bunker fuel was much dirtier and much more viscous, requiring heating to reduce its viscosity before it can be used. Emissions rules for marine diesels are more relaxed than the rules for trucks and locomotives, so they tend to use this crap-grade bunker fuel because it’s cheaper than diesel.
There are many types of fuel (high and low sulfur fuel oil, high and low sulfur diesel oil, and high and low sulfur gas oil). For the most part, the fuel oil is cheapest, and somewhat dirtier than diesel oil (which is generally lower sulfur quantity for the most part I believe, in addition to other stuff).
Many shipping companies are still mired in the recession since 2008, with daily hire rates generally still low. So, they are very concerned with all costs, and fuel is the biggest. With ships burning anywhere from 25-150 metric tons of fuel per day (depending on vessel type), and fuel costing $600-$800 a ton (for high sulfur fuel oil), it’s a very large concern. Low sulfur fuel oil (or diesel oil) is more expensive, and required in several areas (The North Sea/English Channel Sulfur Oxide (SOx) Emission Control Area (SECA), and the North American Emissions Control Area (ECA) are the two largest). This makes fuel cost control even more critical.
Aren’t the giant diesels both more fuel efficient and more reliable than the old steam turbines, especially at the relatively low speeds that freighters, tankers and container ships tend to sail at?
The big diesels can approach 50% efficiency, compared to less than 40% for a steam turbine of a size useful for a ship. Really big turbines can get to 50%, but you only see these in power stations.
Yes but you need to consider that the bunker or residual fuel oil is a large amount of poor quality refined oil product that cannot be used by the land transportation market, hence its lower cost as there is not much demand for the amounts of RFO that are produced. If you start building a large number of ships using very efficient and clean diesel engines you will start to add a significant demand to the diesel fuel markets which will push the price up significantly as there is limited refining capacity for producing diesel products and refinery output can only be balanced so far into producing less gasoline and more diesel. ( that said over the last few years due to increased demand for diesel engine car particularly in Europe refinerys are tilting towards optimizing for distillate production)
That will lead to the margins of using a diesel engine ship being wiped out.
If I remember correctly in '07 and '08 there were significant spikes in diesel prices above the general crude price spikes because there was insufficient electricity generation capacity infrastructure in China so many business there we buying back up diesel fuel generators and hence putting a significant demand on global diesel fuel refining capacity. (my cite would be one of the IEA monthly oil market reports from that period, I just cant remember which one) Lots of diesel ships on the market would do a similar thing.
Caveat - there are quite a lot of grades of fuel oil from essentially distillates that are similar or actually are diesel to heavy grades that are the sludge at the end of the refining process, so if one wants to get picky we need to start talking fuel oil grade, but the main point is more diesel ships will mean more demand for diesel so will push the price up and we will see ship orders adjust, not withstanding the external pressure of environmental legislation.
Merchant ships burn Bunker “C” fuel oil. Steam or Diesel.
Diesel oil is lighter than Bunker “C” which means that it has less BTUs per barrel. And any fuel is purchased by the barrel. So to get the same energy more fuel has to be burned. Diesel in more expensive than bunker oil.
diesel engine rooms are more simple then steam engine rooms. It less manpower to operate an diesel ship, in fact some diesel ships are no man engine rooms. That is no one in the engine room at night. A steam ship requires mor auxalliary equipment.
Deisel engines on ships and ashore are more efficient than steam. Other than coal fired plants new power generation plants are diesel or gas turbine.
Oh yes diesel oil is a refined oil. bunker “C” is what is left after refining crude oil.
Deisel oil does not need to be heated to pump or burn. I do not know at what temperature bunker would need to be heated on deisel engine, but on a steam ship it was heated to 130 degrees to pump and 180 degrees to burn. Which made changing a burner fun because the flash point was around 130 degrees.
And this means that they switch between different fuels depending on if they are out at sea or close to land.
Fahrenheit or Celsius?
A bit tangential, but back in the late 70’s, a friend who worked for a shipping insurance firm (IIRC) told this story. The fuel on big ships is solid at room temperatures (or possibly in colder climates: he was from Seattle). They have heaters or something to keep the fuel liquid. When these fail (which I believe happened due to the engines failing), the fuel solidifies.
This happened and his outfit was called to fix it. The engineers sent him and others in the tank to take a number of detailed measurements. They poured water on top and set off small explosive charges. Bingo, the fuel was liquid, water evaporated, and it was possible to start the ship’s engines again.
He said it was one of those “Check everything 3 times” operations. I guess it doesn’t go well if you get it wrong, especially if you use too little water or too much explosives.
Fahrenheit
When bunker “C” is room temperature is is not quite solid. But it is too thick to be pumped. In fact I have seen water float on bunker “C”.
They make sure the centrifuges are kept in tip top condition.
The USS Midway, built between 1943 & 1945 was originally fueled by bunker oil. Eventually it was converted to burn diesel. As noted earlier, bunker oil has advantages w/regard to cost and potential energy. However, there were disadvantages. The bunker oil sometimes had to be heated to flow to the boilers and the boilers needed more frequent maintenance.
It’s doubtful that the Navy would re-work one of their carriers to use a fuel significantly different than what the rest of the conventionally fueled ships used in that time frame.
What’s more likely is that the Navy as a whole, moved from some heavy grade of bunker oil- like #5, to something much lighter like bunker A, or even something that both steam turbine ships and gas turbine ships can both run.
During the 1960s and 1970s, there was a fairly significant change among the frigates, destroyers and cruisers of the Navy to be gas-turbine powered instead of using the old steam turbines. So it makes sense that a carrier battle group would want to use the same fuel for everything.
Seems like the most environmentally friendly way to propel ships would be to somehow use wind power. I wonder if anyone has ever tried that.