Summon the Ghostly Current ReAq15
Voice/Conc/Ind
Creates a current within the sound of the caster's voice, strong enough to propel a ship forward (or backward) as if floating downstream on a swift-moving river. This spell can also counteract the force of an existing current.
Base 4 +2 Voice, +1 Conc
I'd suggest looking at the Size guidelines for Aquam. Individual without Size modifiers is fine for a small boat (in which case your spell is virtually identical to that in the corebook under the name of "Push of the Gentle Wave", which also mentions a limitation to small boats), but probably not for a whole ship.