Complex sentence: Evansville used to play host to the top tier boat racing circuit of H1 Unlimited when it hosted Thunder on the Ohio along the Ohio River in downtown Evansville, which was hosted continuously from 1979 to 2009.
Split into simpler sentences: Evansville used to play host to the top tier boat racing circuit of H1 Unlimited when it hosted Thunder on the Ohio along the Ohio River in downtown Evansville. Evansville hosted Thunder on the Ohio continuously from 1979 to 2009.