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-   -   Max RPM (https://www.offshoreonly.com/forums/prop-talk/374995-max-rpm.html)

jeffer 03-07-2022 06:50 AM

Max RPM
 
For max. Speed, should my boat be propped to reach max. RPM right where the engine produces its max.HP?

SabrToothSqrl 03-07-2022 08:02 AM

For all about best use, yes. Boat's can't shift (nor would it add top speed), so generally speaking, you prop as big as let's you reach max RPM for the engine.

If you propped lower, you'd be leaving speed on the table (but gain acceleration), and higher, you'd actually be going slower as the engine wouldn't have the power to spin it up, and you'd again be leaving speed on the table.

jeffer 03-07-2022 08:29 AM

Thanks for the reply SaberTooth. So in theory, if my top rpm exceeded the dyno rated rpm for peak HP by more than a couple hundred rpm, I should pitch up the prop?

SB 03-07-2022 09:30 AM

Yes.

Trash 03-07-2022 10:05 AM


Originally Posted by jeffer (Post 4824055)
Thanks for the reply SaberTooth. So in theory, if my top rpm exceeded the dyno rated rpm for peak HP by more than a couple hundred rpm, I should pitch up the prop?

To clarify what SB stated....yes....:D

My personal preference is to error on the slightly underpropped side of things in the most optimal weather / load conditions. Then as loads (passengers/gear) increase or summer heat rolls in performance should still be near peak HP for given atmoshperics.

SB 03-07-2022 01:23 PM

Yup

Griff 03-07-2022 02:38 PM

Since you have dyno sheets, it will also depend on where and how fast torque is falling off.
Post a pic of the dyno sheet

SabrToothSqrl 03-07-2022 03:54 PM

You'll want to do testing with 'real world' scenarios as well. 3/4 tank of fuel, passengers, cargo, etc.


bajaman 03-07-2022 04:52 PM


Originally Posted by Trash (Post 4824076)
To clarify what SB stated....yes....:D

My personal preference is to error on the slightly underpropped side of things in the most optimal weather / load conditions. Then as loads (passengers/gear) increase or summer heat rolls in performance should still be near peak HP for given atmoshperics.

^This

jeffer 03-08-2022 08:03 AM

https://cimg4.ibsrv.net/gimg/www.off...cb657a0f1f.jpg
https://cimg6.ibsrv.net/gimg/www.off...5e602aa982.jpg
Here's the dyno info


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