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#1
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I agree with previous statements as speed will cause walking rather than porpoising. My 20sf will get just shy of 70mph on gps with 2 guys and half a tank of fuel, and will not porpoise, but will start to chine walk if im not careful. just mt 2 cents
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#2
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Wow, 70MPH, that's great. What size engine are you running? I had a 20ft Sceptre with a 200 Yamaha and it would run about 55MPH, it also wouldn't porpoise but had a slight hint of chine walk when low on fuel.
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Steve B 1978 23ft SeaCraft Seavette 502HP ZZ502 Mercruiser TRS Drive-Sold-UGH! 1998 28ft Carolina Classic 7.4 Volvo Penta Duo Prop |
#3
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Yes, I am curious also, what power and what prop?
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#4
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I'm running a 225efi short shaft merc and 14 1/2 x 19 prop. We also had perfect water and cool weather hitting 69.7 on gps at 6100 rpms. Friends have said when running like that with the boat trimmed there isnt a whole lot of boat in the water! However, I have noticed at those speeds there is considerable fuel burn!!
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#5
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Lost, how fast is that seavette with the 502?
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#6
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I've got 64 MPH out of it once, but it will do 63 all of the time with a full tank of gas and porpoising it's a$$ off.
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Steve B 1978 23ft SeaCraft Seavette 502HP ZZ502 Mercruiser TRS Drive-Sold-UGH! 1998 28ft Carolina Classic 7.4 Volvo Penta Duo Prop |
#7
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A little up date, Brett at BBlades sent me a couple of test propellers. He sent me the Mirage plus 21 pitch and a Bravo 1 22 pitch 4 blade.
Here are the results with the Mirage plus: 3000 RPM=30 MPH, 3500 RPM=40.5-41 MPH, WOT=5200 RPM @ 64.7 MPH with drastic porpoising. Even at 30 MPH with the drive all the way down it still wanted to porpoise. Next I switched to the Bravo 1, those results are: 2800 RPM=30MPH, 3500RPM=42.5-43MPH, and WOT=5200RPM @ 63.2MPH with not near as much porpoising. I can even cruise @ 30MPH and trim the drive up some and it doesn't porpoise. Even though I lost a little MPH on top end with the Bravo1 it is by far the best all around prop for my boat. So what Brent wants to do is to Lab finish a 24 pitch Bravo1. He said that I should get more MPH out of it than the Mirage plus and that I should see 66-67 MPH. ![]() ![]()
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Steve B 1978 23ft SeaCraft Seavette 502HP ZZ502 Mercruiser TRS Drive-Sold-UGH! 1998 28ft Carolina Classic 7.4 Volvo Penta Duo Prop |
#8
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According to Merc Racing the Mirage Plus is a maximum bow lifter.
http://www.mercuryracing.com/propellers/mirageplus.php They describe the Bravos and Trophys as 70 mph+ w/ Med bow lift and the 3 and 4 blade cleavers as 80mph+ w/little bow lift Problem might be that their pitches are > 25" and your boat may be heavier than props were designed for. I'd hit the prop guy up for a 3 blade cleaver or a 4 blade trophy or bravo if they make such a thing for stern drives and see doesn't ride a little flatter at the crazy speeds your you're attaining. Again this theory is based on Merc Marketing not my experience. But as long as you got a guy loaning you props - heck, check 'em ![]()
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there's no such thing as normal anymore... |
#9
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[QUOTE]
According to Merc Racing the Mirage Plus is a maximum bow lifter. Judging from how my boat rides, the Mirage+ is a good stern liter. My Michigan Rapture would give me tons of positive trim. I would almost lose the horizon on hole shot not so w/ the Mirage+. I can feel the stern rising w/ the Mirage. It`s a nice feeling. I also think I learned why Denny`s 4 blade Apollo beat my Mirage+ WOT when he did his comparo. 4 blades lift more boat out of the water. Less wetted surface= higher top end. ![]() Steve, do you have room for a 6-71 under the cover? |
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