Actually, it looks like it was one of the boats tourists and locals alike routinely use. According to this article
from the Seattle Times, it was a 112 foot passenger ferry that was in service in Washington State until 2009. I suspect they'll find out the culprit was the driver, as usual, probably maxing the engines for all they were worth, regardless of the hairy conditions that were out there yesterday. Tragic, but not surprising in the least if you've ridden public transport in Africa or ever tried to reason with a bus driver...
I used to have a link to my African rides in my signature line, but every time I check it doesn't work. So, if you want to see Kilimanjaro, the Kilombero Valley, a bunch of short trips around Dar and another long one to Mozambique: go to my profile.