That's the genius: With a faster casting time, we don't need to.
We cast it at night, at first. And even then, only if we can't carry a single extra mage on our ship (Remember, we're throwing all our knowledge at it to improve all its parts) to sustain and direct the storm.
Madman.
Our ships cannot reach the enemy. Sneak attacks might work, but then you're banking on every aspect of your upgrade working, and even then, sneak attacks are less effective than main-battle attacks (mechanically, I mean). You'd also be risking the lives of senior wizards.
So no, I think we do need some way to get into range safely before Storm Strike will be effective.
Anyway, my suggestion for our design. I tried to think of something fancier, but all my ideas required technology we don't have (what I wouldn't give for an electromotor).
Propulsion Tube: This Adamantium tube (made thereof in order to withstand the high pressure within) is inscribed with wind enchantments, that suck air through it at an incredible rate. It tapers slightly at both ends, to create a focused push/pull effect, providing the tube with plenty of forwards momentum.
We shall attach these tubes to the sides of the Alsamma Safina, on special mounts, allowing the tubes to be rotated to be completely vertical, providing max lift, or completely horizontal, providing max speed. This provides the airship with both the carrying capacity and manoeuvrability it needs to be truly effective.