Please note that while the shark diving trips take place in Gansbaai, the whale watching takes place with a different company some 35 minutes away in Hermanus. Also, if you would like to go shark cage diving and whale watching it needs to on a different day.
Most people are unable to go shark diving and then still go whale watching on the same day, without getting very sea sick.
6 hours on the water (4 hours shark diving and 2 hours whale watching) is not possible for 95% of people, and not pleasant for 100% of people.