Thanks BFC, this boat will be light and I should be well under the 2:1 weight to thrust ratio, don't think I'll get to 1:1 helicopter capability though . I'll be cutting a bit deeper, it's a 17-1/2" transom and I plan to make it 9" high. I'm curious if you ever ran the same engine/prop setup between the open hull and deck over setup to compare performance? My son and I can swap props between my 300 Hp 540 on a deck over and his 250 on the open and we use identical pitch settings for the same RPM. One buddy tried to tell me that the 300 must not be making power, but that is not right, she puts out. It's the cleaner airflow into the prop letting her grab.
I plan to integrate the radiator into the seat rigging with electric fans and ducting to keep airflow clean. This will keep me at lower RPM and should help with torque roll. Other advantages will be lower sound signature, faster warm up/cool down and move weight forward. I have been using electric fans in my buggy for years and have had great success.
1 Eye, we are on the same page, understand the tip speed issues and variations. Torque roll is my #1 concern here, I don't want to go all stupid on it and end up with a boat that is not easy on the Capt.One Eyed Gator wrote: ↑Mon Apr 26, 2021 10:08 am... to me each blade has a tip speed it likes for best all-round performance. 76 vs an 80" prop at the same engine rpm have a very different tip speed. Keeping the engine RPM about the same to get best power out of the engine and using the gearbox ratio to dial in the tip speed while also reducing to load of the engine.
Where I tend to agree is a motor with plenty of torque doesn't seems to feel the prop load as much. Specially a smaller diameter need for a deckover to keep the motor as low as possible
I also know that on a round bottom hull and big prop and low gear has quit the pucker factor of torque roll. lol
Just my thoughts
My reference point is 14' Palm Beach hulls built for this motor. Those boats are 4-6" wider (7'-6", 90") to run super wides on 2.68 gear. Torque roll is a bit complex. Starting from a stop in water it is strictly a function of flotation. Once the boat is moving, hydro dynamic lift come into play. On ground it's the outer rail pushing the most.
The worst case is pure flotation from a stop. In this case the extra 6" of hull width increases flotation and the moment arm resisting roll. Torque Roll resistance is "roughly" equivalent to width^2. To match torque roll the comparison is (84/90)^2 = 87% maximum torque. Assuming a 600+ motor the maximum gear equates to 2.68 * 87% = 2.33.
So that's where I am, somewhere between 2:1 to 2.38:1 gear and matching prop, somewhere between 76-79".