A lot of good advice from people more knowledgable than me here.
I have done a survival at sea course and I can concur that getting into a liferaft if you don't know how is not at all easy.
One valuable snippet of information:
If you do have to ditch over a busy waterway, try to ditch near a small motor boat. They are the most manouverable and you stand a good chance of actually making it on board once they get alongside.
Yachts and large commercial vessels are virtually impossible to get into from the sea unless they have a special facility for such.