Irwin built a number of 28 footers. I am not familiar with one designated as a 285 but Irwins that I know in that size range were pretty much strictly coastal cruisers although some where racer/cruisers in their day. Irwin used a lot of nin-directional laminate and minimal internal framing making a 33 year old Irwin less than ideal for a consistent diet of offshore work without some serious remedial work.
What do you mean by "offshore"? I would not cross an ocean in one, but a day or two shot would be a different matter, though the windows would be a concern - they were pretty thin plexiglass on my Irwin.
Offshore meaning: Is this boat strong enough to cruise from Texas to the Carib and island hop.....or, maybe head South to Mexico and Central America????