Provided the inlet is reasonable, you should be able to land some mahi no problem. I have fished offshore of OI for the last 7 years, however my current boat is much smaller and I am only comfortable running the inlet in slick calm seas, as the inlet can become nasty very quickly.
I suggest you purchase a few Islander Tracker trolling lures. You can pick them up at T.W.'s Tackle located at milepost 11 on the main road through the OBX. These lures are trolled on the front of the 3 or 4th wake behind your boat and the Mahi love them. Also, have some cut bait with you. If you see a weedline or any floating debris (and I mean any, like a small piece of wood or plastic bag), motor up to about 50' of it and cast to it. Usually the dolphin will be swimming under it. If you hook a dolphin, keep it in the water until you hook a second one, etc. They are school fish and will show up in hords.
Where to start looking: Head SE out of the inlet until you cross the 2nd color change, its usually about 8-9 miles out. Try trolling along the cleaner side of the color change. Look for water temps in the mid 70's. If you find some concentrations of weeds, also troll around or along the weedline. The dolphin are usually below.
My brother and I will be arriving in the OBX tonight and staying through next weekend, however we will most likely stay inside the inlet with my current boat. If you see two guys in kayaks fishing offshore outside the inlet (2 miles out or so), that may be us. We're hoping to land some pelagics from out Yaks.
If you have any questions, call my cell 240-216-0525. If you have never run the inlet, I suggest you follow a charter out in the AM.
Best of luck.
Matt
Here is a link to the lures http://www.basspro.com/servlet/catalog.TextId?hvarTextId=52807&hvarDept=151&hvarEvent=&hvarClassCode=4&hvarSubCode=1&hvarTarget=browse
