I found this wonderful article that gives a great overview of bulk carriers. A great reference to quickly understand the essential design aspects of a bulk carrier.
I will make one clarification to the article. It mentions that the hull of the bulk carrier may be welded or riveted in some places. I can’t imagine any place that I would recommend riveted construction on a modern vessel. Though I have seen rivets on some older vessels. What about you? Can you think of any situation where rivets are recommended on new ship construction?
The article really does not help you appreciate how fast bulk carriers take on cargo. Literally hundreds of tonnes per hour. Imagine an entire parking lot full of VW beetles, and pour all of them into the cargo hold of a bulk carrier. That gives you an idea of how quickly bulk carriers load cargo. This video is another example:
One of the other concerns for bulk carriers today is ballast water treatment. When not carrying cargo, bulk carriers take on ballast water to keep the ship stable. This can be an environmental problem on long distance voyages. Everything from algae up to small crustaceans can survive the trip in that ballast water. As a result, the ship may introduce invasive species into the environment by carrying them halfway around the world in the ballast water. Recent changes to the IMO regulations require new vessels to have ballast water treatment systems, which sterilize the ballast water. But these systems have limits.
The key problem for ballast water treatment (BWT) is the flowrate. Currently, we are required to treat the ballast water as we pump it on board (and when pumping off in some cases). It isn’t easy to treat ballast water, and matching the flow rate required by a bulk carrier requires massive ballast treatment systems. The bulk carrier would need to give up an entire pair of ballast tanks just to handle all the machinery. And don’t forget the cost of all that equipment. Your BWT should not be larger than the main engine. This will be a problem for future ships. I know some companies are discussing options to load untreated ballast water and then cycle it through the treatment system once inside the tanks. It will be very interesting to see what solutions develop.
If you want to learn more about the challenges of ballast water treatment with bulk carriers, I know of two free papers that provide at detailed analysis with four example installations. (Fair disclosure, I helped to author the papers.)