Hello all! If you go to michigan prop web site there is prop claculator helper to assist you in your prop quest.
On Nov 22, 3:53 pm, john hamilton <[EMAIL PROTECTED]> wrote: > It's more complicated than that. The boat is going to use x amount of > horsepower to go y fast. It doesn't care what rpm that is. The engines will > use x amount of fuel to produce y horsepower. What you want is to produce > the amount of horsepower required to go y fast as efficiently as possible. > The term for this is BSFC. Best BSFC (brake specific fuel consumption) > numbers are usually at or around the peak torque RMP. Where that is depends > upon your camshaft, but with a stock marine cam it is probably near your > current cruising RPM. You want your boat propped so that the best BSFC > number is the rpm where you cruise at, assuming your hull and transmission > ratio allow it. I had a camshaft custom made so that my peak torque comes in > @ 2500 and the torque curve is very flat, particularly between 2500 and 3500 > rpm. I'm propping it to cruise at around 2800-3000 rpm or so, even though > the way I built the engine it achieves peak horsepower @ > 5000 rpm. I think the torque peak is more important than the horsepower > peak and the torque curve is what I focused on when I designed the engine. I > expect you're propped correctly, assuming your engines are stock Chrysler > Marine Engines. With those fuel flows you're running twin 440's? > > John > > --- On Sat, 11/22/08, Rocco <[EMAIL PROTECTED]> wrote: > > From: Rocco <[EMAIL PROTECTED]> > Subject: [UnifliteWorld] Prop sizing > To: "UnifliteWorld" <[email protected]> > Date: Saturday, November 22, 2008, 2:25 PM > > Here it is again, the ever so often discussion about prop sizing. > I've read lots of info on this subject but I can't find the one piece > I need. > > My boat is propped properly - so I'm told - and achieves 4600 RPM @ > WOT. However, except for the occasional whoppie moment when I run it > up to full speed - 26KTS and 60GPM - I consistantly cruise between > 2800-3200 RPM. At these RPMs the boat cruises 12-13 KTS @ > appoximately .5/gpm. > > I think my hull is very efficient considering its top speed. Speed > goes up quickly above 3200 RPM but then secondaries open and the fuel > consumption rises even faster. > > So, what's the problem with over-propping the boat so WOT is say 4000 > RPM or so? If I continue to run between 2800-3200 RPM won't I get and > increase in speed which will result in better mileage? I know the > engine will be working harder at the same RPMs but there should be > some gain in gpm. no? --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/UnifliteWorld?hl=en -~----------~----~----~----~------~----~------~--~---
