Best Cruising mph/rpm

Canaboater

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Joined
Jul 26, 2016
Messages
3
Hi boaters ....
I have a new to me 1992 25' crownline 250cr 7.4L (330hp)..bravo II.... I'm getting 5000 rpm at wot trimmed up hitting 43mph with a little throtle left... Now if I slow the throtle down to let's say 25-30mph would I also trim down? Or do I try to get the drive as high as possible before it starts bouncing....what should my rpm/mph cruising range be??? When on a plane should my drive be always as high as possible.... Any advise would be helpful thanks....
 
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Bondo

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Apr 17, 2002
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70,470
Ayuh,.... Welcome Aboard,..... Generally speakin', most hulls get the best cruise economy at 'bout 3200/ 3500 rpms,.....

Sounds like ya need more prop pitch,....

Havin' throttle left, ain't really Wot,....

Ya should be propped to 4800 rpms at Wot,... No throttle left,....
 

Canaboater

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Jul 26, 2016
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3
Hi bondo thanks.... If I were to keep the same prop for the remainder of the season (September here) but kept my rpms in range of what the 7.4 can handle my guess no harm would be done other than burning more fuel???
 
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Rick Stephens

Admiral
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Aug 13, 2013
Messages
6,118
You are correct bout no harm done by having a too low pitch prop. Just keep it in recommended RPM range so you don't add unnecessary wear to your motor. Many boaters run a prop that can easily over rev their engine so they have more acceleration and responsiveness at lower speeds.

Keeping your carb out of the secondaries will maximize fuel efficiency. If injected or carbed it is mostly a matter of finding the most efficient speed for your hull, probably somewhere between 3k and 3.5k. I've been running some cruise/fuel use tests on a newly repowered smaller boat. It is interesting how a small increase in throttle can change the fuel usage. Still learning since I don't run the boat all that often, but my best seems to be 32 MPH at 3200 RPM. Nice part for me, 32 MPH was WOT at 4700 RPM with the 3.0L motor. While the 4.3 can use a lot more fuel, and your 7.4L a lot more yet, they are pretty efficient when run in that range. Start leaning on your throttle and fuel use per mile starts to jump higher.
 

bruceb58

Supreme Mariner
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Mar 5, 2006
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30,454
For the boat in my signature, I have a flow meter and the best MPG calculated by the flow meter combined with GPS is around 3500 RPM. For each change in throttle, I have to tweak the trim to peak out the MPG.

My boat has duoprops so that may make a difference compared to your boat.
 
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Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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47,309
If your boat, prop, drive, and motor combination was tested on boattest.com, then they will have tested it and the cruise RPM will be listed there
 

stonyloam

Vice Admiral
Joined
Mar 13, 2009
Messages
5,827
Generally speaking at any given speed if you trim for maximum rpm at a given throttle setting you will be close to optimum. Make small adjustments and wait a few seconds to see if you get a change.
 
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