Portsmouth to St Malo is the longest channel crossing but have a look at the Brittany Ferries website. It gives you details of all their crossings and options. We have used Brittany Ferries many times in the past and have found them very good but now find them quite expensive. This year we are using the Condor fast ferry from Poole to St Malo - 4.5 hours but it does not sail in very bad weather. The fast ferries tend to roll a bit more than conventional ferries, hence the nick name 'The Vomit Comet'!!!! We have used Condor ferries several times and ,touch wood, have never seen anyone with a problem. The catering on Brittany ferries is much better than Condor, particularly Brittany ferries restaurant, but that's no problem for us othe Condor 4.5 hour crossing.