I have done whale and dolphin watching through the ship and had very good success. I saw nine whales and many dolphins. My tour did either early morning or lunchtime tours. We chose the later one.
The only reason I booked this tour was because of all the sightings over the years from other passengers I had spoken to. And it was fabulous.
I looked into doing it independently but it was just a few dollars cheaper for a much smaller boat.
Hope your lucky.