Hi Dave
We are booked on our return crossing this Thursday. When we came over last July Ange started this topic http://www.canalworld.net/forums/index.php?showtopic=31194&st=0&p=547769&fromsearch=1entry547769 on the subject as she was concerned about it.
We got an awful lot of great advice and there are links to other peoples experiences. We also posted photos of our journey which will give you an idea of what to expect.
We had a very calm day for our crossing and we all enjoyed the day.
We went to Preston Marina to get flares, as recommended in the guide, but the guy there said nobody bothers and even if you got swept out of the estuary you would just end up on the sands at low tide (and become a tourist attraction for the day).
Read the skippers guide have a full tank of fuel and water so that if the engine gets hot you can run the hot water to provide extra cooling, that's assuming you have a calorifier.
Enjoy the day, take some photos and post about your experiences on here please.
Hope this helps
Dave