[dredmorbius]

The "middle passage" portion of the slave trade saw ~15% mortality, though that would have been high for non-slave passenger travel.

https://en.wikipedia.org/wiki/Middle_Passage

Deaths at sea definitely occurred. Credible accurate records don't seem to be available however, as this article's abstract notes:

Farley Grubb, "Morbidity and Mortality on the North Atlantic Passage: Eighteenth-Century German Immigration" (1987). https://www.jstor.org/stable/204611