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Comments
Go Steelers!!!
Thanks JMichels and Handy, for the information. I have a 2009 320 with 5.7 MAG MPI motors coupled to B2 drives with 21 pitch aluminum props that are not cupped. The boat performs well but I would like to get on plane with less bow rise and pick up some efficiency at cruise speed. Unfortunately, my boat is all tucked away for the winter so a slip test will have to wait until I launch in the spring.
In either case you would likely definately benefit at the very least from stainless props versus aluminum for less distortion and flex.
my 4x3 props were on my 03 Rinker 270. Worked very well.
I put in a few gear ratios to see what mine might be. I have an 18.75 diameter prop. Says the 2.0 is not possible. I think the 1.6 looks most realistic, how about you guys?
@LaRea will tell you to run fast because less slippage is better fuel economy.
the ron hill pleasure five, 19p/14.25" is impressive... according to tach and gear ratio, it has single digit slip- like, between 6 and 8%. on plane, and anywhere from 2250 RPM (where it starts to fall off plane) all the way to max RPM with that prop which is right at 5k RPM... it's good for right at 52mph on slick water... the water cuts right under my seat on the 212 when it's fairly slick surface and trimmed up right.
a 3 blade 21p stiletto in 14.25" is a pig out of the hole, and though it can push around 60mph at 4800~4900RPM, it's a bit of a..... liar... they are marketed as '21p' and take a hit for out of the hole performance compared to other 21p of the same class... because they're really not 21p at all.... the one i have is 22.5p as measured by a prop shop as 'mean' pitch across the blade... it was 'new out of the box'... the cupping is also significant and the rake is ridiculous... at the bitter end of RPMs, and playing with the trim to maximize RPM, it too is around 8% slip... it struggles to hold plane under 2800RPM and the slipping it significant up until 3600~4000rpm where it bites in and trim can be finessed to the least drag possible. the bow of the boat is high and the water cuts perhaps a foot to a foot and a half behind my seat on slick surface and trimmed just right...
between those two, i can get my best economy... the three blade stiletto offers better economy if i get on plane and stay there and above 40mph compared to the five blade trying to do the same thing... however, if there is traffic on the water or i have to drop off plane often- or- i have clear path and can settle the throttle around 3kRPM and cruise, the five blade is far superior in terms of economy.... as an example, i made a 28mile run two weekends in a row now, one with the stiletto and another with the ron hill.. the stiletto impressed as the motor spun it fine and drank 10.5gallons for that run... i didn't know how much difference the five blade would be, but it turns out it only drank a touch over 8 for the exact same route. fairness, again: i had to drop off plane several times with the 3 blade, where i only came down once i recall when it was the five blades turn.
the third screw i run is a Fury... 21p... it has some stupid huge vents and i can't find the plugs for them (if i ever had them in the first place)... the diameter is smaller- perhaps 14.125 and the cupping nor rake isn't as significant as the stiletto nor the ron hill.. i'd likely have more purpose for this prop if i could plug those vents, and because i can easily 'blow it out' coming out of the hole and can blow it out a bit if i punch it hard while on plane- i guess the exhaust pressure breaks the water tension for a second or two?.... now, in fairness, if i had to select JUST one prop i 'may' be inclined to choose this one IF i could plug those vents effectively... bonus: i don't have exhaust bellows, i just have a tube... the only place this prop is disadvantaged is from lower speeds and below plane where the tube is shoved into the lower unit.. trimmed up (north of 40ish MPH) it's free and clear..
the Ron Hill 5 blade is far superior overall... i just keep the stiletto around for when i want to run fast... that happens sometimes... okay, a lot.
i share all of that just to say- there is no perfect prop for everything... there is a perfect prop for it's perfect application... that said? anything over 15% slip from 75% throttle up needs to be addressed. at least with a non-duo outdrive...... also a little tidbit: my ratio is 1.62:1, which is why i can spin that stiletto nearing 5k RPMs (that and some help on the valve train with rollers and a little higher ratio rockers than the stock 1.5:1's).