I was actually referring to boattest.com, and was not pointing at you. One of my biggest pet peeves is guys that claim good fuel economy from straight inboards. Done in this thread by multiple guys. It's simply not true. That does not mean I am anti-inboard. I am anti-inboard for speed maybe. But primarily I just want data, not conjecture stated as fact. Drives me nuts. Another example, where there is "data" is the claim of better shallow water attributes for an inboard. How? Maybe less draft at full speed, but I can bounce off stuff with an I/O at low speed with the drive up and not hurt anything. Try that with an inboard.
In the interest of full disclosure, there was another similar thread recently. A guy claimed that a tournament boat (IB) may deliver better fuel economy at the lowest planing speeds where he would be pulling a waker or tuber. That in fact might be true, so there are exceptions. But overall? No way. Not even flippin' close.
I think you answer some of your own questions though in the first post as there is kind of a horsepower limit. Almost all 25 - 35 ft planing hulls are twin I/O though. Start to run out of support by customers and builders above 40 ft. But there are exceptions for sure. Also, there seems to be less advantage with trim when you go this big. You could argue the fastest and largest ocean racers are almost all I/O.
Odd, but you go oven bigger and jets make a showing. I am not clear on when they crossover for efficiency and benefits, but there are many examples in the largest super yachts. Another interesting point is the largest ship in the world is indeed a single screw inboard. Uses the largest engine in the world which dispels some other myths as it is a two stroke and is the most efficient diesel engine I believe as well.
