Are there any rules in 5th ed so far for ship handling? What I am interested in is what rolls would be needed for a ship to survive various classes of weather phenomena, for example a severe storm? Also does nay supplement cover crew sizes etc? I guess I should know this, but I'm tired today and I don't! 
cj x
If you are interested in the mundane aspects, Mythic Seas (4th edition) is fairly good here. Trade rules and mythicness is quite bad, but for crew size et al makes a fairly nice job
Xavi
City & Guild is your best bet.
The answer is on page 7, Ease Factors.
Don't worry about whether a typhoon is Hard (12), a cyclone is Very Hard (15), and a hurricane is Impressive (18) - especially since there are no wind-meters in Medieval Europe to measure the Beaufort Scale! You, as SG, determine if it's an Average difficulty storm or an Almost Impossible difficulty storm, or what, and go from there.
Quite possible that keeping the target number will be a sliding scale, and the result will depend on the level of success - a legendary roll will keep the ship intact, an above average to keep it afloat but with some damage, and a poor roll means she's going under. Maybe "hard" for the crew to climb the rigging and "very hard" to save the sails, but only "average" to keep the ship from sinking entirely - etc. (This is also good to keep the saga from ending with the drowning of 3/4 of the characters, if you're worried about that. Just don't specify the target numbers, keep a straight face, and appear impartial when you give them the bad news.)