This brief history of the Black Rock slave ship, and a description of it's disappearance is revealed on the site:
The Black Rock was one of the three 19th century slave vessels thought to be owned by the New World Sea Traders. The Black Rock usually sailed from its berth in Portsmouth, Britain to Africa, then on to the Americas or the Pacific Ocean. By the 1880s, its operations focused on the Indian Ocean, where the presence of US and British navies was not as strong. The final voyage of the Black Rock involved the ship leaving Portsmouth and travelling to the South Indian Ocean. The ship collected gold from the mines in Indonesia and Papua New Guinea, which was to be exchanged for slave in Africa. However, instead of sailing west to Africa, the ship left port in an easterly direction. It was never seen again.