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Old 11-20-2018, 12:24 PM   #19
Bkay
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City: Reedville, VA
Country: United States
Vessel Name: Pending...
Vessel Model: Between Boats
Join Date: Aug 2018
Posts: 330
Quote:
Originally Posted by Insequent View Post
Good luck with the build.

I would have the 4045's rated at M3. They will not use any more fuel, and there is potentially a little more top speed if you want it.
Thank you. We are in the final stages of layout and cutting files should be built within a few days.

Regarding the rating - of course you are right that it wouldn't cost me anything in terms of fuel to rate at M3 and I'd have some additional speed. But my logic is I could rate at M3 and have 200 hp at 2500 RPM - but I don't really need that speed.

Alternatively, I could rate at M1 and only be able to turn up to 2300 RPM and hit my target speed. But at the same time, we will also increase propeller pitch so the engine was fully loaded at 2300 (I honestly don't know if they go for 100% load at WOT or something slightly less; but it will be more pitch than if I were in an M3 engine that was fully loaded at 2500 RPM).

So at any RPM up to 2300, I will be more fully loaded and will travel faster on essentially the same fuel burn as an M3 engine. Your right, I can't go OVER 2300 RPM with my engine - but not going over 2300 because I don't want to or not going over because I can't is immaterial.

In reality, if the John Deere 150 hp engine was still available I would have chosen that. Overall you are probably right in that I might have been better off with M3 or M4 rating - but I'm not one to pine over speed I don't have and we optimized the hull shape for this speed then found the best engine that would produce the required HP.
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