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4 blade vs 5 blade

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Old 10-20-2011, 07:25 PM
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Default 4 blade vs 5 blade

ok im sure this has been discussed before but please give me any input you have....i have a 38 scarab kv with 1.50 drives 32 bravo props and extension boxes....im looking to increase my cruising speed....any do and don'ts about 5 blade opposed to 4 blades....what size 5 blades do i start with if i decide to go that route....
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Old 10-20-2011, 07:36 PM
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32" Maximus.
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Old 10-20-2011, 07:40 PM
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I'm not sure this will help but I'll give you the results for my 38 Fountain with 525's staggard. The boat has 1.50 gears and standard Bravo drives and was delivered with 32P Bravos. The boat ran 91.3 best every and at 4000 RPM it ran 52MPH. I went to 30 PX5 Hydromotive props and at 4000RPM's I now run 62MPH but top end dropped to 89MPH. I like the cruise speed and all though I wish top end was better I'll take the cruise increase all day long. It is important to note that the 91.3MPH top speed was when the boat was new and it now has close to 400 hours on it so performance may be down on the engines some. Also, the boat accelerates much better with the 5 blade Hydros.

Hope that help some.

Oh, one more thing you might want to know...with the 32P Bravos my top RPM was 5400+..meaning every now and then I would bump the rev limiter. Now with the 30P Hydros my top RPM is 5300-5400 but have not ever hit the rev limiter.
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Old 10-20-2011, 07:45 PM
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sounds good...its spinning the 32's on the rev limiters at 5800 so i dont know how much more it can turn them....the boat has 540/800hp blower motors.....whats up with all the talk about the 5blades eat drives....any truth to that??
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Old 10-20-2011, 07:52 PM
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seadated....what r's do you turn on top end? how many peeps and fuel do you usually have in the boat? thanks
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Old 10-20-2011, 08:25 PM
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MrSeakAttack

The boat turns very well at speed but I have never made a sharp turn at full speed. I do make ajustments for trafic, channel requirments, etc at high speed with no jumping/hopping it just make nice smooth turns.

I would say 90% of the time I have 3/4 to full tanks and four "peeps".

FYI...my boat is a 2004 and was sold as staggered engine but now is considered a 3/4 staggered bacause after 2005/6 they went full staggered. See pic.


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Old 10-20-2011, 08:35 PM
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I have heard all about 5 blades eating drive too but really a lot of it comes down to the driver. If the props are hooked up tight and you slam the throttles fwd all that torque is tough on the drives. If your drives are a little loose and you slam the throttles foward you'll get a bunch of RPM's but it will take a while for the boat to gain speed like mine...not to hard on the drives. Also, coming out of the hole is the critical point...ease it up = longivity. My .02
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Old 10-20-2011, 08:43 PM
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nice set up you have.....thanks for the input...i'll keep you posted
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Old 10-21-2011, 01:26 AM
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Quote:
Originally Posted by SeaDated View Post
I'm not sure this will help but I'll give you the results for my 38 Fountain with 525's staggard. The boat has 1.50 gears and standard Bravo drives and was delivered with 32P Bravos. The boat ran 91.3 best every and at 4000 RPM it ran 52MPH. I went to 30 PX5 Hydromotive props and at 4000RPM's I now run 62MPH but top end dropped to 89MPH. I like the cruise speed and all though I wish top end was better I'll take the cruise increase all day long. It is important to note that the 91.3MPH top speed was when the boat was new and it now has close to 400 hours on it so performance may be down on the engines some. Also, the boat accelerates much better with the 5 blade Hydros.

Hope that help some.

Oh, one more thing you might want to know...with the 32P Bravos my top RPM was 5400+..meaning every now and then I would bump the rev limiter. Now with the 30P Hydros my top RPM is 5300-5400 but have not ever hit the rev limiter.
WOW your slip numbers are off the scale with 4 blades at cruise-35%, I thought my boat had alot of slip turning 4000 rpm's at 58-60 with a 30 pitch and 1.50 gears, yours was definately a candidate for 5 blades. As far as your boat eating drives, with only 525's that shouldn't be a big issue even driving hard.
Now, as far as Mr sneak attack, with 800 hp hi tq blower motors it might be a different story, heavy boat, fairly high power, 5 blades, low slip= twisted off vert or prop shaft no matter how good he is on the sticks, broken shafts are not just a "myth" Smitty
What drives, assuming bravo ones?
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Last edited by articfriends; 10-21-2011 at 01:56 AM.
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Old 10-21-2011, 01:54 AM
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Arctic being super knowledgable - and one of the very few guys on this site that really knows this drive perfectly is absolutely right.

I would say sneak attack is in for a set of bills that will make him wince with a 5 blade 800 HP deal.

My Imor 710 in a 5300 lb twin step V (it's loaded like a caddy ) is capable of laying waste to a fully built Bravo in 50 hours with a 4 blade and moderate throttling in the chop and waves on the pacific ocean. To be fair 50 fairly tough hours of boating.

I tried a 27 p5 x and was thrilled with its cruise and bite, but 5 blade would have eaten it even quicker

With a 4 blade Lake lifespans are markedly better like triple Im at 100 hours with no shavings so far with 80/20 Lakes this year.

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