The need for profits in the 18th century's Atlantic market economy drove changes in ship designs and in managing human cargo, which included enslaved Africans and the mostly white crew. Improvements in air flow on board the ships helped to decrease the infamous mortality rate that these ships had become known for throughout the 16th and 17th centuries. The new designs that allowed ships to navigate faster and into rivers' mouths ensured access to many more enslaving posts along the West African coast. The monetary value of enslaved Africans on any given American auction-block during the mid-18th century ranged between $800 and $1,200, which in modern times would be equivalent to $32,000–48,000 per person ($100 then is now worth $4,000 due to inflation). Therefore, ship captains and investors sought technologies that would protect their human cargo.