[3Jane]

The channel is a piece of cake, I can never see why people avoid it. It is actually more risky getting past Dunkirk with the amount patrolling boats there than it is passing Calais. Having done that, the straights of Dover and the rest of the channel is easy.
After passing out of range of the armed trawlers around Boulogne you can reduce to the best economical speed for your boat. As long as you keep your watch crews fresh you can avoid most potential threats on the surface even in daylight with careful thinking, except aircraft of course. Spending the daylight hours submerged is actually preferable, not so much as being safer but for the amount of single merchant traffic you will pick up by hydrophone which you would miss on the surface even in clear conditions. All the time from Wilhelmshaven 39 to the transfer to Lorient in either a VIIB or a IXB, it works every time.
Arrive between 23:00 and no later then 01:00 stay exactly 3000 meters out from about 8 Km before Calais all the way through. Travel with decks awash at full ahead (reduced by being decks awash to about 10 Kts). Once through, surface fully and away.