On our sail north from the Azores, we saw whales most days.

 

On one occasion, 3 huge fin whales followed us for 50 minutes.  Difficult to estimate size but they were around 20+ metres long; certainly made our boat feel very small.   The turquoise colour is the under-belly of one whale as it went under the boat.

 

The video is a bit shaky - we were more than a little nervous:

 

YouTube link:  http://youtu.be/KTLUIvY_Jrc