The spell's Target parameter is one aspect of its targets. Its Form is another, that is equally important. Rarely T: Room, T: Structure and T: Boundary spells target all of a place - most of the time they target specific types of beings, things and general stuff in a place. Wards and the Aegis are rather an exception here, treated by the Magical Wards chapter and the Aegis description of ArM5.
You can't without a house rule or at least a Major Breakthrough (see ArM5 p.161 last paragraph). But if an Aegis for your ship is of utmost important for your saga, such a Breakthrough could in your saga well have already been accomplished by a follower of Notatus.
Such a breakthough better be kept secret in a small cabal! Movable Aegides in general can also revolutionize magical warfare by siege towers, assault ships, flying fortresses (with magical bombs!) and magical digging machines protected by such Aegides!