Acid-Catalyzed Hydration Is there any particular reason why this mechanism is used in the solution manual rather than an acid-catalyzed hydration? 



I was thinking of having the double bond attack a hydronium ion, which would create a carbocation. This would then create a place for water to attack. Finally, the water would be attacked by water to reform hydronium ion. 

Why wouldn't this work?

Does this have anything to do with the fused ring?
Acid catalyzed hydration probably would work, but might well be accompanied by other materials derived from the carbocation intermediate, such as rearrangement and elimination products, which would make this route less desirable.  The mercuric acetate route does not involve free carbocations, so such side products will not contaminate the desired product.