We have sailed through the Bay of Biscay 5 times, and it has been wonderfully smooth every tim.
Your journey will be smooth, although it may be a bit choppy when sailing through the Bay of Biscay. If you suffer from sea-sickness there are lots of remedies to prevent it - ask your pharmacist for more information.
Ive sailed the med and the atlantic and every time in the med we hit rough weather. We did the atlantic last month and even the bay of biscay was calm probably the smoothest cruise I have ever done.
We did the Oceana/Canaries cruise. I was fine but my husband was sea sick crossing the Bay of Biscay. I would recommend buying/getting prescription for anti sea sickness tablets before you travel. If you are on other medication the Dr on board (who was very pleasant) may not be willing to give you tablets - my husband had to have an injection.
A lot of cruises to the Canaries include calling at Vigo.This means crossing the Bay of Biscay. Unfortunately there is never a right time to cross the Bay.We have crossed in December when it was like a millpond and also in June when it was particularly rough.I am afraid you just have to take pot luck.