Ocean Alexander 44' CPMY Performance

I realize your question has been here since May, but...

I have a 1992 39' OA with twin 250hp Cummins. It's the same boat as the 42 or 44 cockpit models, but doesn't have a cockpit. We cruise at 12knots and burn 12 gph. That seems to be the sweet spot for fuel economy.

I'm afraid we don't build boats in Detroit

You don't calculate based on what the manufacturer's might have projected. You do that based on actual experience. Based on monitoring fuel flow. Actual, real world. Now you use experienced estimates in selecting a boat.

As to learning the systems, most of the equipment has manuals. But learning how boat systems in total work is a long time thing. There are courses that could help advance that learning. Watch mechanics who work on your boat and learn. If you venture out far take someone who has experience, but in the size and type boat you're looking at I'd expect you'll be inland or ICW.

There are probably manuals on the engines available and on other equipment but there isn't one that tells you how to work on everything. As to comparing to cars, owner manuals don't tell you that either. Now the manufacturers service manuals and some private label manuals do. But a lot more of any car model sold than of the top boat model. Manuals for 20 year old cars aren't all that easy to gather either.

No that is not what I'm telling you. I'm telling you there are estimates available, but that's all they are. At the best they vary based on load and conditions. In actuality they may vary more based on a particular hull or specific pair of engines. It will very based on how well tuned the engine is. Sometimes engines are even detuned initially to increase range and durability. This is no different than estimated car mileage. You can't take the numbers on the sticker and bank on using them and not running out. I'm saying you don't plan a trip at sea based on those estimates. You use actual experience to confirm or change or build more estimates. That was intended as a precautionary warning to you. You will be talking to brokers and sellers and they'll give you numbers. All the number you get will be ballpark. But if you're wanting some guaranteed numbers and one manual that came with the boat that includes every item on the boat including detailed instructions on how you can fix everything, that's just not available. That isn't on a car either. You buy a car and you get an operator's manual. The service manuals generally cover parts of the car but there are no single manuals that cover all components.

Sorry you take offense at my answer. I'll leave others to answer you now and I will bow out of your threads and questions completely.