It is very easy to get from Dumaguete to Bohol by ferry, Weesam Express leaves Dumaguete bound for Bohol every afternoon at 1.30pm. The Fare is P400 one way
Website:
WEESAM EXPRESS :: Index
Another way to get from Dumaguete to Bohol by ferry is with Ocean Jet, they leave Dumaguete at 3.00PM every afternoon as well and they arrive in Bohol at 4.40PM - the fare is P520 one way.
Website:
Ocean Jet
Either way, a couple of hours by ferry is pretty easy. I would choose Weesam Express, both for the lower fare but also getting to Bohol earlier is definately a plus.