I have a 1991 F322 with 350 crusaders and also turning 16X16 Nibrals. With 1.52 to 1 transmissions. As you guys know it comes down to how much those blades are pushing the water and what effiect rpm the engine can run at and still turn the props with smooth torque. Just imagine if you put a 20 inch wheel on the shaft "Don't think it would fit" but You would not get high enough rpm out of the engine because it could not maintain enough torque to spin that big proppeller. That is why they engineered the power train the way they did. For example when the 350CID is turning 3000rpm through a 1.52 reduction the actual shaft rpm is only 1973 Rpms turning that 16 inch blade 16 inch through the water every revolution it turns minus slippage. The engineered that based on boat displacement, hull types, Load, etc.... That is why they always recommend your engine could reach 3800-4200 rpm @ Wot to see if you have the right propeller. Too much rpm add another Degee of pitch , Too little rpm take it out. Another example would be the same boat with diesels would operate at a lower rpm but turn a larger prop due to the diesels higher torque ratting.
As far as speeds I can get 19.0-20.5 knots at 3000 rpm and burn 9-10 gph a engine on no wind or wave waters. Avg speed on trips with loaded boat is 18- 19.5 knots to maintain 1 Mpg "Gps is tied in with the Flow scans". Sometimes I push up to 3150 rpm if I can increase speed to 22-23 knots while still maintain 1 mpg. Any higher than that the 4 barrels open up and the start to burn 12, 13, 14 gph each engine. The boat definetly feels real good at 20 plus knots as far as it rides. As far as top speed I can honestly say I hit 29.6 knots once and mid 28's the other times I tries. I probably opened it up 4-6 times just to see my rpms. The stbd engine was re built professional 1n 2007the port has 726 hrs on her.
Trim tabs in my opinion are used more than you think to keep the nose down. I say this because 3 season ago my stbd line bursted open and failed. With out the tabs my speed was down and fuel consumption was up. I could only go 16 knots if I did not want to eat more fuel. We were 90 miles form home port so I loaded the forward berth with much weight as possilbe to keep the nose down. You can laugh but I was going down the chester river with a hard Stbd list to try to keep the bow down. Well there it is.
