Historians have a difficult task, if not all facts have been discovered yet, with doing what? not publish the findings until all evidence and facts are discovered. make up missing pieces of information depending on the bias of the writer. attempt to re-create a historic event to find what probably happened. write only the true evidence from as many perspectives as possible.

Historians should have an impartial viewpoint and use as many details as possible while describing an Historic event, this is hard to achieve especially when there is not enough information (like documents, pictures, reports, etc.) that they can use to reconstruct the order of events. That's why they Attempt to re-create a historic event to find what probably happened. However, these are only hypothesis and new discoveries can prove if they are wrong or right.  

the enslaved people onboard suffered from illness with some frequency

equal area projections

equal-area projection. a projection in which regions on the earth's surface that are of equal area are represented as equal.