Hi folks and thanks for all the encouragement. It wasn't until after I had posted the Scurvy idea that I found that it had already been suggested earlier.
Don't want to be plagiarising the ideas of others now do we...
Well I had a look at what cards were currently being used and the ideas around. I have not seen (as yet) a reference to ships being "Becalmed".
There is Favorable Winds which give 5% additional speed. I am sure that against this there were times when ships were stuck with no winds for days on end and crews went out for a little rowing exercise towing the ship to find a location where the wind picked up again.
Seem to remember film scenes in "Moby ****" and "Mutiny on the Bounty" where being Becalmed was a real danger and hazard to sailors.
It is another idea to kick about and let others contribute.
Another idea is brewing now... lol