Originally Posted by BrentAshurst
i just bought a 97 maxum 2300sr it has a 5.7 motor(not the mag just the regular 350) alpha 1 out drive. i went to the river and it topped out at 30 mph at 4000 rpms. i checked the prop it has a 15 on it and the guy i bought it from had a spare that was a 16. both are 3 blades, my question is with the boat loaded up full tank and 10-13 people could i still get the boat to plane out if i went to a 4 blade 19 or 20? i waisted alot of fuel running that high of rpm but it is a big boat and i dont want to have it lugging around. what do most people run(propeller wise) on a boat this size and whats the rpm and speed?
Where you running 30mph @ 4000 rpms with 10-13 people on board, or is this more of a theoretical question? How many people and approx. how much gear, fuel and water were on board when you were running those numbers? A Merc 5.7 (either carb or EFI) should have a max. RPM range of 4400-4800 RPM's.
going up in pitch is going to give you slower hole shots and be slower to get up on plane. It should allow you to run at higher speeds, or at slightly lower RPM's for the same speed as a lower pitch prop. There is, however a law of diminishing returns which applies here. You Don't want a situation where the prop pitch is so high that you run UNDER the Max/ RPM range at Wide open Throttle (WOT). If you were reaching 3800-4000 RPM's at WOT, then you'd really be overpropped and straining the engine. If Max RPM's at WOT are over 4800, you'd be underpropped and over-revving the engine. Either are not healthy for the motor.
These numbers are all relative to thea amount of weight that is on the boat. Think of trying to pull the boat and trailer with a Honda Civic, vs a Ford 350. I would first start with 1/2 fuel, 1/2 Water, minimal gear and 2 people and get the boat up on plane. The get it to WOT and see where the RPM's are running. proper drive trim and tabs will help. Keep in mind current, water conditions will also slightly impact the numbers. See where you are from there.
In my opinion 10-13 is too many for that boat. It would be too many for my 2800. I wouldn't expect the 2800 to get up on plane with that many people on board.