If you want to spend the whole trip in the BVI, why would you start in St. Thomas? If you're looking at a longer charter of 10 days+, and you intend to spend at least a few nights in the USVI, this may make sense. But if your intent is to pick up the boat in St. Thomas and make a bee-line straight for the BVI, I'm not sure why you would charter from a St. Thomas based company rather than starting your search on Tortola with one of the many great charter companies there. Customs is one thing, but then you also have to factor in the sailing time to/from the BVI on each end as well.