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Old 10-21-2011, 07:29 AM
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artic and uncle dave

i spend most of the time on a river and small lake.....i will take the boat out in 2 weeks to get real numbers at cruising but it seems to me its gonna be in the 55mph range at 4000rpms....so my slippage is high i guess because of my extension boxes therefore i was leaning for 5 blade props but i dont want to be changing shafts and gears everyother time out also...i may get my current props reworked and go from there but at the same time i could put that money towards a set of 5 blades...break out another thousand
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Old 10-21-2011, 08:57 AM
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artic and uncle dave

i spend most of the time on a river and small lake.....i will take the boat out in 2 weeks to get real numbers at cruising but it seems to me its gonna be in the 55mph range at 4000rpms....so my slippage is high i guess because of my extension boxes therefore i was leaning for 5 blade props but i dont want to be changing shafts and gears everyother time out also...i may get my current props reworked and go from there but at the same time i could put that money towards a set of 5 blades...break out another thousand
What has been done to your drives so far? If your slippage is too high you might need to buy 5 blades, in my opinion it sorta depends on what your slip numbers are afterwards too. Back when my boat only had 950 hp,I tried a 28 pitch 5 blade Maximus vs the 30/32 Bravos I usually ran, when I took it out to test it, damn, my slip went from its normal 18-22% to 8%-11% and after ten passes / 30 minutes I sheared off a billet Max Worx prop shaft. Now, it does depend on how you drive like Seadated mentions except in your case you do have 800 hp/and I'm sure just as much tq so even if you take it "easy" unless you don't ever hold throttle wide open you will put more strain on the drive with lower slip numbers. Now if your slip is at 30% and it ends up at 20% it might not be as much of a issue vs 10%. Have you considered drive spacers? Did you install the boxes, did you have a gain vs without them, Smitty
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Old 10-21-2011, 09:09 AM
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What has been done to your drives so far? If your slippage is too high you might need to buy 5 blades, in my opinion it sorta depends on what your slip numbers are afterwards too. Back when my boat only had 950 hp,I tried a 28 pitch 5 blade Maximus vs the 30/32 Bravos I usually ran, when I took it out to test it, damn, my slip went from its normal 18-22% to 8%-11% and after ten passes / 30 minutes I sheared off a billet Max Worx prop shaft. Now, it does depend on how you drive like Seadated mentions except in your case you do have 800 hp/and I'm sure just as much tq so even if you take it "easy" unless you don't ever hold throttle wide open you will put more strain on the drive with lower slip numbers. Now if your slip is at 30% and it ends up at 20% it might not be as much of a issue vs 10%. Have you considered drive spacers? Did you install the boxes, did you have a gain vs without them, Smitty
Isnt 18-22% alot even for a 4 blade?
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Old 10-21-2011, 10:55 AM
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Single engined...v-hull...stepped hull...tend to be fastest around the high teens for slip.

I have done alot of testing on my Nordic...it does a consistant 105...and slip is around 19% at full speed.

Arctic friends has done a lot of testing...and his slip is right there.

The Howard Bullet that did nearly 130 mph+/-, and is still the fastest single engined v-hull that I know of ....had slip numbers around 21%.

I am the fastest with a merc lab prop...and use a five blade (p5-x) for pulling my kids on an inner-tube.

The prop I most normally use is just a standard bravo....it hooks up better in the low and mid-range than the lab prop.

Chris

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Old 10-21-2011, 10:58 AM
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Isnt 18-22% alot even for a 4 blade?
Yes, it is for a top end slip number. Not unusual for cruising rpms. Most props go up in slip when the rpm's drop. All things being equal. Some hull's work better with a higher slip number of fx. 14-16% slip. I recall having a long talk with Julie @ Throttle Up a few years ago about this, when dialing in a friends 38 Lightning. For your hull, it's too high.
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Old 10-21-2011, 05:41 PM
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I have tried different things that lowered my slip and gained ZERO speed or lost , broke part faster and torque loaded boat. My boat and drive is pretty happy around 20% and can hit 100mph (almost), twin engine might be a different story. The 35% that Sea dated had seems horrible, I can't imagine having 32 pitch props and cruising at 52 mph at 4000 rpm's, that boat was BEGGING for bigger props!! I would still like to hear what Mr sneakattack has for drives, heavy boat with 800 hp, if he can afford it buy beefier drives (scx or Konrad) and find the best prop be it a 5 blade or 6 blade even, Smitty

Last edited by articfriends; 10-21-2011 at 06:07 PM.
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Old 10-21-2011, 06:01 PM
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bravo's...i know ball bust is coming i understand....i had a b max with my cat and it held up good with 900 true horsepower....so future plan is maybe b maxes....
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Old 10-21-2011, 10:33 PM
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Yes, it is for a top end slip number. Not unusual for cruising rpms. Most props go up in slip when the rpm's drop. All things being equal. Some hull's work better with a higher slip number of fx. 14-16% slip. I recall having a long talk with Julie @ Throttle Up a few years ago about this, when dialing in a friends 38 Lightning. For your hull, it's too high.
I am carrying the bow better now after adding a spacer. But I cant get good speeds with more slip now at 17% - I assume due to more hull dragging. CB-BLR, your hull is a lot more advanced and shorter (less bow to carry)

I assume a 272 with 900 HP can carry the bow due to so much horsepower at speed.
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Old 10-22-2011, 12:27 AM
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if you are on the rev limiters all the time I would try a set of 32" p5x if not try 31". the maximus is a much bigger prop and i would start with a 30" if you decide to try those but they really hook up well and may put to much load on your drives.

my boat no step 37 ft center console at 40mph with 26" bravos 20% slip 3100 rpm, with 24" maximus 10% slip at 2950 rpm.
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Old 11-02-2011, 08:16 PM
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update....i took the props off and brought them to a local prop shop and have found out they have been reworked and were only 30.5 pitch props.....so my slip isnt the issue....im getting them pitched to 33's and hopefully run this weekend and go from there..
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