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Old 06-10-2020, 04:37 PM   #21
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My example was not the same RPM.....it was the same speed at a lower RPM for the overpropped boat. I was in no way advocating for overpropping. Just discussing and going through a mental exercise. I want to know what people think....by using their brain....not regurgitating everything they've been told.
Soorrrry, but I never claimed to be a mechanical engineer!!
Enjoy your day.
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Old 06-10-2020, 04:39 PM   #22
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Soorrrry, but I never claimed to be a mechanical engineer!!
Enjoy your day.
Todo bien mi amigo!!!! Y buenos dias!!!!
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Old 06-11-2020, 05:50 AM   #23
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"It's still overpropping relative to the manufacturer specs, but depending on the engine, boat and usage patterns, it's not necessarily inappropriate."

Very true but the engine mfg prefers their system as it reduces warranty repairs on certain styles of vessel operation. And is much safer with a novice operating the vessel.

A boat that needs most or all of the engines rated HP and is usually operated at high power does well with the MFG rated RPM for the props. Sport fish , ski towing , police or military operations.

An engine that will be operated at a tiny fraction of the rared HP will live long and prosper producing the minor HP at far lower RPM.

Depending on the boat there can be a 300-500 RPM difference at cruise .

The lower RPM at cruise makes a big difference in noise on board , better fuel burn and engine life.

One early method of contemplating engine life was piston travel miles.

2100 RPM vs 1600 RPM , big difference in engine wear!

As is a 200HP engine being screamed to burn 2 GPH , for 30-35HP.
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Old 06-11-2020, 08:53 AM   #24
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It’s sorta like you’re gett’in someth’in for noth’in Fred.
Baybe you are.
Do you really think you’re getting more engine life putzing about at 12-1400rpm?
And how much fuel are ya saving .... 10 gallons a year?
And the manufacturers recommend prop to WOT to avoid pesky customer relations? So you take those troubles yourself and all’s well.
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Old 06-12-2020, 05:17 AM   #25
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"Do you really think you’re getting more engine life putzing about at 12-1400rpm?"

On modern trucks and buses with electronic injection and a turbo the engine mfg seem to think so.

Most new transportation diesels is designed to cruise at 1200 rpm or so.
Automatic trans and loads of gears allow the engines to run at torque peak most of the time.

A cruising boat usually only needs to propel the boat at one speed , selecting a prop and tranny match is smart , but assumes a trained operator.

Converted farm or light truck equipment was never built to to operate at full tilt , so why pretend screaming it is required for long life and low fuel burn?
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Old 06-12-2020, 07:19 AM   #26
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Chugging along at low RPM in an overpropped boat is likely a higher load than a typical sustained automotive cruise load. Well, unless the boat is massively overpowered for its intended use and hull design.
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Old 06-13-2020, 05:10 AM   #27
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"Chugging along at low RPM in an overpropped boat is likely a higher load than a typical sustained automotive cruise load. Well, unless the boat is massively overpowered for its intended use and hull design."

Many of the old TT claim 2 GPH at normal cruise that's 30-35HP from a 135HP engine " massively overpowered for its intended use and hull design."???
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