Programmed images on grain of sand which trigger when sand falls down (or any object which you bind illusion to) can work and can cause mayhem. Mirage Arcana other hand needs specific location (which can be large mobile structure like a ship). Also just note the weapons on ship you can conjure gets halved dmg in underwater (like usual underwater combat) and half of usual range unless their piercing (you got 2 ballistas so their not affected).<br/><br/>The catapult and cannons stats I think can be found in heroes of battle (I did not specify what kind catapult so I let you choose). Overall weapons are non-magical in nature. Albeit cannons may have alchemical ammunitions.