Trying to estimate range

You should only be in the ICW for a short bit getting from Beaufort NC to the Neusse River then from the sound just South of Coinjock into Norfolk. Fill in Ft Laud, top off in Ft Pierce, that should get you to St Augustine, if it looks like you're running low, you can top off in Cape Canaveral. St Aug to Charleston, fill there with a back up stop at Fernandino (easy and fast in and out) or Hilton Head. Charlston to Beaufort NC with back up stop just inside the Cape Fear River, this also gives the option of cutting inside through Snows Cut and getting out the other side of Frying Pan Shoal ( though with your draft, that's not really necessary). From Beaufort up Adams Creek to the Neusse River and take the Pamlico and Albermarle Sounds up to the ICW just south of Coinjock, you can fuel there if necessary (if the timing works out to spend the night, there's good food there as well) or just keep going another 38 or so miles to Great Bridge and fuel there. Once you come out of the locks, it's pretty much all slow bell until you get to Norfolk, I stay at the Tidewater Marina, most of the transient docks they can fuel you in your slip (same for Beaufort) or when I get there at the end of the day, they usually have me tie up at the fuel dock. From there, it's an easy half day run into Ocean City.

Running inside on the ICW is a big slow fuel consuming PITA unless you plan to run 8 kts the whole way, I just don't do it anymore. If the weather is too bad to run on the outside, I just wait. The only day it saves me is between Norfolk and Beaufort and if I take the ICW route, it doesn't because of all the up and down for the sailboaters who are afraid to sail.

Spot on Henning, you have made that trip more than a few times obviously!
I would try to keep the runs less than 200nm. per day which should be well within your fuel capacity. All those stops also have great food so an early arrival has fringe bemefits. St Augustine, Charleston, Beaufort, with a quick pit stop at the Oregon Inlet fishing center before heading outside would be my first choice, weather permitting. Call the charter fleet on 18/72 for help getting in there, don't try it on your own!
Be careful if using the Snows cut route inside Cape Fear. I know of a few boats that piled up on the backside of the Carolina Beach inlet in the ICW this winter.
Save wear and tear on your throttles and run outside. I wore out a set of Morse controls in one trip inside! Not to mention all the bridge tenders chastizing you for "unnecessary openings". Always thought it was kind of ludicrous, nearly every mast you pass doesn't have any sailcloth apparent.

I didn't say only, I said best. Maybe your owner wants you to run 10 kts, but none of the people I run for want to wait 3 weeks for their boat to get there. $10k is kinda a drop in the bucket in terms of annual cost of running most of these boats. Besides, on a 61' VSC running 30kts I use less than 4000 gallons between Miami and Glen Cove LI. Even at $3 a gallon, (Didn't make the run last year, but April 09 runs the average fuel price on the trip was $2.70) that only comes to $12k for the trip at speed. I tried going slow once but in order to get into real fuel economy I had to slow to 8.5 kts (through the water, which means on the trip N when you have to run up all those rivers, you lose an extra knot+) and the owner didn't want that many hours put on the boat plus he wanted it there, so after a day of that he said "screw that, get it here." There's also all those bridges in N an S Carolina. When the wind is blowing strong enough to keep me from running offshore, those bridges are locked down with boats piled up and being blown on the bank, running into each other. If the wind is an offshore flow, I run near the beach in pretty smooth water listening to all the radio calls of collissions and to Sea Tow to get them ungrounded. It has never taken me more than 8 days running the route I described and that is sitting for 4 days and running for 4 days, and usually I run mid April and end Oct-early Nov. Trying to run at speed on the inside is even greater wear and tear and fuel consumption than the outside because you're always up and down for slow bells and and slow boats. The ICW may be scenic, but I'm not getting paid for scenic (besides, I saw it plenty pushing Benzine barges up it), I'm getting paid to do a job, and that's what deliveries are, a job.

I am not an expert like some of the guys who posted, but we have taken our boat from MD to FL and back recently and are about to head from MD to FL in a couple of weeks. We have a similar size boat and HP engines as your Ocean and also cruise at 20 knts.

I prefer Hennings route but I think some of his stopping points are more than 10 hour runs at 20 knts when you consider getting to and from the inlets and offshore. You might think about Ft Laud to Cape Cannaveral, then to Fernadino. You miss St Augustine which is nice but if you are going straight from Ft Laud it is a very long run at 20 knts. Fernadino to Charleston is a nice run and gets you in early enough to go out for a bit. Then the run to Beaufort NC is doable in a day but you could break it up with an easy day to Georgetown or Myrtle Beach. We usually spend one day on the inside between Ft Laud and Beaufort just to break things up or if weather is an issue.

From Beaufort to Norfolk as Henning said but you might think about taking the Alligator river instead of the Pamlico sound as it can get pretty steep in even modest winds. The Alligator river route is on plane almost the entire time and is at most an hour longer but more scenic and faster if the winds start up. Good food in Coinjock and Norfolk is a nice town.

You can pretty much figure 2nmpg. I've never seen a boat like that that wouldn't do 250 miles. If you fill in Ft Lauderdale and refill in Ft Pierce, you'll be able to get a reasonable fuel consumption figure to use for the rest of the voyage.

Alligator river isn't bad, and with your draft shouldn't pose a problem, but when you get to Middle Ground on the top side of Alligator River Swing bridge, the "magenta line" on the charts is incorrect and puts you on a very shallow shoal. Last few years I went through there I pulled someone off every time. Stick to the green side as the markers are and it was good. Running the sounds though saved me enough time that I could make it through Great Bridge before the evening lock down and before the Norfolk Southern bridge goes down for about an hour and a half for three trains that run in the evening (they don't like opening between those trains, sometimes you luck out and commercial traffic comes through and you can go with them. I have waited there up to 2 hrs before.) into Norfolk to fuel before closing so I can leave first AM at 0 dark thirty. Figure from the first bridge you hit at around MM 20 to MM 0 at Tidewater Marina is an average trip of 4 hrs. I have made it in as little as 2 and as long as 7 for that 20 mile stretch. I like being at that first bridge for the noon opening. The other advantage you get with the Alligator River route though is another fuel stop just on the top side of it.

I would guess you'd be burning 45gph. I would say 520 gallons should be usable. I would run 10 hrs a day max, which should give you a fuel safety margin to account for rough weather etc etc......so probably a very safe or conservative range of 210NM and actual of 250NM

I've been skipping Charleston a lot and going into Georgetown, SC. The problem with the inlets in SC, is the distance you have to run from the Seabuoy to the Marinas.......

Exactly, with a lot of it being slow bell. That's why the Cape Fear river inlet is good, there are several marinas close with one right inside the inlet.

NO, the surveyor reports the boat cruises at 23 MPH, not "tops out at" WOT. I ran a 48' Ocean express about 6 years ago with the same 671's and it cruised at just under 25 knots at 1950pms......

It depends on how you trim the boat with the trim tabs to gain speed, how the bottom is (cleanliness) and how much weight you have on board. I would never run a 671 100rpm's off of WOT. I would run them 1950rpms...... With DD's it really depends on cruise speed.

The biggest thing that makes them (Detroit Diesels) come apart is very large changes in load factor and acompanying change leading to high EGT's. For example if cruising at 1900 rpm's the boat is barely on plane and when it goes up a wave it slows down 2 knots, and when it goes down the wave it gains 4 knots. That destroys them. Most DD mechanics say cruising them at say 2000 rpms (which I don't) is better if the boat stays fully on plane and a consistent SOG, then 1950 and it's laboring. Same reason you see 12v92's on a 58' Viking SF that cruises at say 28 knots, they last 3000 hours. And, on a big, beamy, and heavy 58' Striker SF I ran that cruised at 19 knots at 1950, but did the whole speed up speed down deal, the boat had 8 sets of major overhauls since 1991, because they got loaded up and down a lot. In 5' seas the speed would go up to 21 or 22 knots at times and sometimes slowed down to 17 knots........Backing down on a fish and sending all of that vibration through the shafts to the engines is a huge killer.

Just about every Ocean SF brand new, topped out a 30 knots back then WOT. That was their calling. It should cruise at 1950 rpms at 25 knots, the one I ran did. It was an express with a full tuna tower. Even full of fuel with the trim tabs down. The problem with Oceans and I've run more then a few, is that overtime they keep losing speed.......(I don't know if the hull absorbs weight or what. I managed a 63' Ocean SF 1988 that at a year old cruised at 26 knots and topped out at 31knots......then the next year would only cruise at 24 knots......then in the end (2008 when the boat was sold) would only cruise at 20 knots and 24 knots tops......even after major overhauls......