The whole of the west coast of France is worth seeing at some point or another..
however you really need to decide what department you are planning on visiting first as each department along the coast offers a different kind of enjoyment....
We favour the Brittany coastline as it offers nearly everything you could want for on a day out in a boat...stunning coastline, loads of isolated islands to explore, fantastic wildlife and great food (and even better cider!
)
The Basse Normandie coastline has its advantages too, the Cotentin peninsular (from Caen westwards around the coast till you get to Avranches) has some beutifull coastline too and, if you have the boat for it, could be your gateway to the Channel islands.
PM sent to you re; requirements and regulations
Simon