Man, you've got some high-powered advisors helping you out here. And they all agree! Each one has raised a valid, interesting point that pieces the puzzle together. That's what I love about this board! I too am trying to understand how all these pieces fit together. This is what I think I understand.
To go a certain speed (100 mph, why not) you must overcome hull drag. Hull drag is made up of aerodynamic drag, water drag on the hull itself and the water drag on the drive. Each of these drags can be broken down into different types of drag but let's not. I'm going to say that you can't do much about aerodynamic drag, you trim the drive to reduce wetted surface (drag on the hull) and you raise the drive to reduce drag on the drive. We all know that. Whatever this ideally low hull drag is, we now need an equal amount of thrust to overcome it and achieve the speed.
Now it gets interesting. If you ask a naval architect what the most important factor is in choosing a prop, he will say "blade area". That's where the thrust comes from. Blade area in the water. We manipulate the amount of blade area by changing diameter, the number of blades and by raising the drive and prop. Too much blade area and slip % is low, but you are slow because you are using to much of your power turning the blade. Too little blade area and slip % is high and you know the rest.
In the old days, the only way we would trim the drive to get the bow up, and even though we were giving up some of our forward thrust, the net result was more speed because we reduced wetted surface drag and maybe drive drag. We all knew how to find this sweet spot. This was with three blade props because with the drives deep they gave us all the blade area we needed.
The high drives on todays vee hulls reduce drive drag, but they also reduce leverage for trimming the bow up. Trimming up too much just causes more slip and/or blowout. So steps are used to reduce hull drag. The only drawback of the high drives is the props are now too high, so we have go to four blade props to get the required blade area in the water.
If raising the drives is good, why not raise them some more? We are doing this, and the results are good, but once again we have raised the props, so five blades are needed to get the required blade area in the water for the thrust we need.
The fastests boats use aerodynamic lift to reduce wetted surface drag, and surface drives to reduce drive drag. They are using huge diameter four and five blade props to get enough blade area.
Each of these different hull types has a different range of ideal slip %. The old vee hull with submerged three blademight be 15%, the step vee with raised four blade might be 10% and the racing cat with surface drive might be 5%. (Just guessing)
So, to summarize, your boat shouldn't need much drive trim and you don't want to give up the forward thrust anyway. Let the hull design take care of hull drag. When these guys are telling you to try four blades, or get Hering to rework the props, or maybe even raise the drives more for the five blades, they are saying get the blade area right for whatever drive height you are running.
It has been said on this board before, I don't remember who, that you start out with too much blade area, cut until the speed stops increasing, then buy a new set of props and don't cut them quite as much! Not something I'd want to do to a set of Herings.
Anyway, thanks for sharing your dial-in experience with us, and good luck.
Hey Ted, how's it going?