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It is porpoising, that's why it's losing speed in chop, chop doesn't eat up speed, wind eats of speed, shorties work on #6 drives great but not XR's, XR shorties are design for control not speed, it allows you less trim tabs on drag because on the singles shorties create more prop roll, but they are easier to drive because there's less to do, hit it and go, then trim the drive, if you're referring to the Blackhawk, they can't take any power. The Max 5 prop is not the Maximus prop, apples and oranges. Hydroconic cutting will give you your RPMs, if the motor is boosted, add power by switching to ethanol.
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A 30P at the standard #4 will be your 29P, but it will take a #8 cup on a 28P to make it 29P, this will increase stern lift going this route so the diffuser ring might have to be grinded down.
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It took Brett awhile to get back to me but he is super busy and he did call me today and he agrees that I should go down to a 28p Bravo 1, run it and get some numbers (I love the Rinda test tach function!) and send it back for some work if needed. I will probably have a like new, labbed, 30p Bravo 1 for sale in the spring! Thanks for all of the advice.
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Originally Posted by thirdchildhood
(Post 4766934)
There are other factors such as the -2" Imco lower. Dropping two pitch numbers would put me all over the rev limiter. The fact that I can turn 5,390 RPM now, when it's safe to run a lot of trim, tells me that I'm close. The rev limiter starts pulling power at 5,400 so I was 10 RPMs short of that and everyone tells me to run the 525 as close to 5,400 as I can. The problem is that I can't run that much trim on rough water. I need 300 more RPM, or one pitch lower. At least that's my understanding of it. Rhinda tool indicated that I was still at 100% power at 5,390 and 82.0 MPH. I have had this boat as high as 85.6 MPH in perfect conditions and I think bumping the rev limiter.
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I may have missed it but do you have a shorty on the drive now? From reading this I agree with griff and endeavor. Unless reaching that high rpm is trimmed so high it could be stressful on the u-joint, but doesn’t sound like you have to trim that far.
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Originally Posted by Griff
(Post 4769699)
That sounds perfectly normal and perfectly dialed in to me. The only thing you are going to gain dropping to a 28 is more rpm and then it will hit the rev limiter when you trim it out. You have slightly better acceleration, but you will hit the rev limiter before you see the same top speeds.
Originally Posted by IGetWet
(Post 4769701)
I may have missed it but do you have a shorty on the drive now? From reading this I agree with griff and endeavor. Unless reaching that high rpm is trimmed so high it could be stressful on the u-joint, but doesn’t sound like you have to trim that far.
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My $0.02......$60 to test a BBlades prop is probably cheaper and more definitive than cutting down a prop.... and once you know exactly what prop spec you need, if you ding it, you just order a standard and readily available PN
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Originally Posted by thirdchildhood
(Post 4769726)
But wouldn't you think that if I could get my RPMs to 5,400 without insane trim and 20% slip that I would go faster? Maybe there would be more forward thrust as long as I can keep the bow high.
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Originally Posted by Griff
(Post 4769759)
No, because you would be spinning a smaller pitch prop. Deduct .5 of pitch for Bravo props since they are stamped on the heavy side.
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It never hurts to try, but I doubt you will see much, if any, change in top speed in rougher water. With your "realistic trim" you were at 79mph @ 5000rpms = 15% slip. Your slip numbers really shouldn't change using the same model of prop with 2" less pitch at the same trim level unless the lab recipe is causing a little more prop slip.
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