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23 Mirage to 24 Bravo

Old 08-30-2020, 11:14 PM
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Default 23 Mirage to 24 Bravo

Boat is an '87 Baja Sport220 with Bravo One outdrive that's been raised 2". Basic 330hp 454 that was rebuilt before I bought it. Started the evening with a 23 Mirage that's was worked on in some way before I bought the boat. Ran 60mph @ 4950rpm at optimum trim. Found a spot and swapped props to an as built 24 Bravo One. Picked up to 65.6mph @ 4600rpm at optimum trim. With the bravo it wants very little trim compared to the Mirage and you can really feel the boat pop loose at the right spot and just one bump up from there is where it ran the fastest. The Bravo won't blow out or cavatate even with full trim from idle. And tucked under bow rise is substantially less with the Bravo while planing. So at this point very happy with the change. This is my first stern drive so it's gonna be a learn curve of sorts.
So, what should I try next? Want to learn as much as I can this year before I add power next year.
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Old 08-30-2020, 11:39 PM
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TRy next?? nothing, 65 is a good speed for that boat with that motor at that rpm. If its handling well, your golden.
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Old 09-08-2020, 10:39 PM
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Is that a GPS speed?? Because your prop slip is only 2-6% which is nearly impossible on a V bottom.
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Old 09-08-2020, 10:49 PM
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Originally Posted by Griff View Post
Is that a GPS speed?? Because your prop slip is only 2-6% which is nearly impossible on a V bottom.
Yes, it on GPS. It's a shallow V with only 14 dead rise. If that matters. Merc calculator shows it to be 6%. So what you saying is I shouldn't let anything happen to this prop?
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Old 09-09-2020, 01:40 AM
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Originally Posted by Smitty275 View Post
Yes, it on GPS. It's a shallow V with only 14 dead rise. If that matters. Merc calculator shows it to be 6%. So what you saying is I shouldn't let anything happen to this prop?
Prop slip calculator shows 6% if you use the stamped pitch of 24". In reality most box stock 24 Bravo's actually measure more like 23.2" so then its 2%.

I would have the prop measured to see exactly where it specs out and then have it fully balanced and maybe thin the blades slightly. You might pick up another 3 mph.
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Old 09-09-2020, 03:13 AM
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Thanks Griff. That's the kind of info I was hoping to get. I've been away from boating for about 25yrs and there's a huge learning curve to get ahold of. I'd like to milk everything out of what's there before I go adding another 200hp that's capable of running 5500rpm.
That 25yr hiatus was building racing engines and porting cylinder heads.
Thanks again,
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Old 09-09-2020, 08:35 AM
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Tach maybe reading a little off too for low slip data??
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