A five hour delay on a short route does seem unusual but if there is no replacement ship available then that's it. Yes, you sit around for five hours and get there at 2am but the alternative is the flight is cancelled and you have to be rebooked on another flight or deal with it yourself and apply for the refund etc.
To the best of my knowledge, it's something of a policy in Aer Arann that they will always try to get there the passenger there, eventually, on the flight that they booked. It seems like a bit silly at times, but aparrently the passengers appreciate the effort. Another example - take a Dublin-Cork flight. If Cork is fogged in, many airlines would simply cancel the flight and bus or train the passengers down. Aer Arann will get their plane in the air, fly it to Cork, go back to Dublin or divert to Kerry or Waterford and then arrange to get the passengers to Cork from there.