I started working on this project in a blog last week. I'll try to get a bit more done today.
First off, someone pointed out the article I referenced from Slate was from 2003. I thought it was from 2008. Guess it's time to get my eyes checked.
Also, in my last blog I included the BDTI and BCTI as part of the BDI, but as this is the dry index, and BDTI and BCTI covers tankers, they should not be in the mix.
Here is what makes up the BDI - (Baltic Exchange Dry Index)
It's daily assessments from various selected charter brokers of the previous days "fixtures" (chartering contracts), for 4 sizes of dry bulk ships (listed below). Bulk, meaning the cargo is not in containers. Generally it's coal, ores or grains.
Capesize BCI (Baltic Cape Index)
Vessels which must transit via the Capes. (Time to get out the world map).
Either the Cape of Good Hope, which is at the tip of Africa, or Cape Horn, which is at the tip of South America. These ships are considered too big to fit through the canals. Some may be able to transit the Suez, depending on their draft (meaning, how deep of water they require), which varies depending on how much cargo they have onboard.
Panamax BPI (Baltic Panamax Index)
Vessels which can just fit through the Panama Canal. Actually, I find this term misleading, as it would seem to mean they are too big for the canal.
Supramax BSI (Baltic Supramax Index)
These vessels use to be called Handymax, but for some reason in 2005/2006 the Baltic Exchange changed the term to Supramax (I do not know why). These vessels are smaller
than Panamax, but bigger than Handysize.
Handysize BHSI (Baltic HandySize Index)
These are the smallest of the dry bulk vessels and are very versatile. They are small enough as to be able to get into any port.
Here is a link to Vessel Size Groups which gives more detailed information. However it based on categories from 2000, and therefore does not have the Supramax category.