Complex sentence: Britain, having won the 1927 race in Venice, then became the subsequent host for the contest, the 1929 venue for the Schneider Trophy was RAF Calshot, which is on the eastern entrance to Southampton Water.
Split into simpler sentences: Britain, having won the 1927 race, became the subsequent host for the contest. The 1929 venue for the was RAF Calshot, on the eastern entrance to Southampton Water.