Not getting full rpm and wondering about prop size

[Hallawzy]

I have a 1994 rinker with a new 5.7 yamaha 300hp short block installed have a yahama out drive with 1.5 gearing. And run a ss 14 3/4 in prop x 19. I run wot at 4400 rpm at 51 mph with half tank and me alone. With 6 grown adults at wot 4500 rpm at 45. mph. I tried a four blade 23 pitch 14 inch and could not get on plan. Would like to get rpms up to the 4800.witch way should I go with prop? I have a great hole shot now but would like more speed trying to get to 60. I know I need more then a prop but want to start their. Am I about right with speed and rpm now?

 

[steelespike]

4400 at 51 = 3% slip, Highly unlikely,.Normal slip is usually about 12%. When slip is really low the tach is suspect.
If the slip is really high the tach is suspect.
If we guess 12% slip it calculates to about 4800 rpm. It's possible the rpm is even higher.
We need to verify the tach and is the speed by gps?
Tell us about the Rinker. Size, dry weight Is the hull designed for speed? Is it a deep V about 18 degrees at the transom?
Is the motor fully broken in?

 

[Hallawzy]

With GPS I got the mph, I have not checked the rpm guage. When I hit 51 on GPS the rpm guage was around 45- 4600. was bouncing that was on a half tank of gas. The boat weighs 2675 dry weight. The motor should be broken in its got last year use and this year's use on it.

 

[Hallawzy]

Thanks for the help I would believe it's my tack. What would happen if I went to a 21 pitch prop. Would it give me more speed or slow me down.

 

[steelespike]

Not knowing your actual rpm Its difficult to tell your results with a 21. If we assume your at least at 4800 it probably give a little more speed.Calculates at 56 mph.@ 4800, 12% slip.But that 4800 is suspect because we are assuming your already at 4800
so a 21' prop would lower your rpm.
​ And may sacrifice some hole shot and rpm.
If your 19" rpm is actually way high you have a better chance of seeing 60.But will take more than a 21" to do it at 4800.
We just need to confirm your actual rpm with the 19" prop.