The most famous place to whale watch is Hermanus, but not because there are necessarily any more whales there than anywhere else on the Overberg coast but simply because the land based (i.e. from a cliff top) whale watching is exceptionally good. You’re looking at again a two hour drive from Cape Town to Hermanus so that makes it a day trip at least. You can also do boat based and kayak based whale watching in Hermanus too: have a look this company: http://www.percytours.com/kayaking-with-whales-in-hermanus.html
Alternatively, you can if you’re lucky still see some whales in False Bay, which is closer to Cape Town from Simonstown. Have a look at this site to see what you think of this option. http://www.boatcompany.co.za/i_whaleviewing.html
There’s a really good site which gives you lots of information on all the types of whales you can see near Cape Town here: www.whaleroute.com
We can book and plan any kind of whale experience you’d like: just ask!