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Old 03-21-2011, 11:08 PM
  #31  
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the center of your prop shaft should be 1.75 inches above the bottom of the sponson with 12 inch stand off boxes. also should be running a nose cone. all AO 3100s prior to 2000 were set up with the prop shaft 1" to 1.5" below the bottom of the sponson. 2000 and later with no extension boxes were set up with the prop shaft level with the bottom of the sponson and 1 to 1.75 above the bottom with 8 to 12 inch boxes..

Last edited by quest; 03-22-2011 at 05:33 PM.
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Old 03-23-2011, 11:46 PM
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Great information as I have been following the posts.... I have had several of these 3100's and different applications in each. The question currently is I have a 2002 where the x is a bit higher as you mentioned Quest in your post. Can I get away with imco boxes and -2 sportmaster shorties and 4 blade bravos? I have also heard and experienced in my past cutting off the ring defuser to help get on plane and cut some of the slip out. I care little about my past boats as they had been set up differently, but this one is an 02 and more than likely I am looking to put stock 500efi's or preferably 575sci's. I am putting together a stock application and may boost on the power a touch to gain a few extra hp's! I have a family now vs. the old days so running 130 is less likely than my recent past. Obvioulsy I am looking to maximize performance yet still have a safe application which equals.... (wife off my a$$ and me having more fun)
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Old 03-24-2011, 10:58 PM
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cutting 1/2 to 3/4 inches off the difusser ring will give you a little more bow lift at the same trim position. this will allow you to reduce the positive trim slightly and result in slightly more speed. it will make it slightly harder to get on plane not easier. I always cut off this much from my trim rings. the extension boxes will allow you to just barely get away with the 2 inch shorties but you might have to add a 1/2 inch spacer. had one boat with the prop shaft 2 1/4 inch above the sponsons and it just barely worked. thats why I recommend 1.75 inches. 5 blade herrings will cure the getting on plane problems and might even make the 2 inch shorties work perfectly well with the extension boxes.
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Old 03-24-2011, 11:39 PM
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[QUOTE=quest;3359160]cutting 1/2 to 3/4 inches off the difusser ring will give you a little more bow lift at the same trim position. this will allow you to reduce the positive trim slightly and result in slightly more speed. it will make it slightly harder to get on plane not easier. I always cut off this much from my trim rings.

I'm in the process sending my B1 labbed 32's to merc for a tune up. Is there anything else that should be done to the props to help performance while there?
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Old 03-25-2011, 11:07 AM
  #35  
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I'm in the process sending my B1 labbed 32's to merc for a tune up. Is there anything else that should be done to the props to help performance while there?[/QUOTE]

I had 34 Labbed B1's on my 31 Awesome, & I had Brett @ Bblades put a bit of cupping on the tips to help carry the bow & helped planing as well, the more leverage you have to carry the bow, the sooner you will pack more air & get out of the porpoise range, hope this helps
(BTW mine had no boxes & -2 shorties)
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Old 03-25-2011, 01:18 PM
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Originally Posted by Ran-Dom 32
I'm in the process sending my B1 labbed 32's to merc for a tune up. Is there anything else that should be done to the props to help performance while there?
I had 34 Labbed B1's on my 31 Awesome, & I had Brett @ Bblades put a bit of cupping on the tips to help carry the bow & helped planing as well, the more leverage you have to carry the bow, the sooner you will pack more air & get out of the porpoise range, hope this helps
(BTW mine had no boxes & -2 shorties)[/QUOTE]

Randy, are you turning props out or in? When turning out I had more stern lift with cupped blades. When turning in it seemed to suck the stern down thus creating more natural ow lift.
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Old 03-25-2011, 08:05 PM
  #37  
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I was turning out, I tried in but the boat felt weird, & there was no difference in top speed
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Old 03-25-2011, 09:11 PM
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Default Prop rotation on a 31' Cat

Anytime I see a thread or post discussion on prop rotation on one our type of Cats, I re-read the following post from the "Great Moments of Cat History" by T2x (Rich Luhrs).

.--My thoughts on "spinning" in..... Simple physics.... Right hand rotation propellers,torque (lean) the boat to the left. Left hand rotation propellers torque the boat to the right. In a twin engine boat spinning outboard or , RH on right side, LH on left, the torque of the propellers tends to return the boat to level when one side or the other leans outward. When props are spun inboard RH on left, LH on right, or counter rotated the torque tends to make the lean worse. This occurs because as a boat(Cat or Vee) leans to one side, the prop on that side buries deeper and exerts more force, while the prop on the other side rises (in some cases out of the water) and exerts less force. So...... If a RH prop is spinning on the right side of a boat leaning to the right, the prop tends to push the hull back over to the left. (spinning Outboard). If, however, the left hand prop is on the right side in a right hand lean , the prop tends to continue to roll the boat over. I submit that this is why there has been such a dramatic increase in barrel rolls (even in straight-aways) in races in recent years. When I flew over races for 16 years, I could always spot the counter rotated boats, because they behaved very differently (and definitely not better)than their properly spun (outboard rotation) competitors.
The reason that many people spin them "backwards" is the fact that on some hulls the boat may gain a mile or two per hour at top speed....or..... the boat has a bottom tune that needs more bow lift. The speed can generally be achieved in other ways without using an unnatural rotation as a "bandaid" (This is particularly problematical on stepped bottom boats that skid first, then catch suddenly, then roll outward......get the picture?)
One can re-tune most bottoms to add rocker to provide bow lift without resorting to ill advised prop rotation changes.
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Old 03-25-2011, 10:55 PM
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Originally Posted by Ran-Dom 32
I was turning out, I tried in but the boat felt weird, & there was no difference in top speed
Did you in fact notice the bow carry higher? I am very conscious of how my boat reacts to different running conditions; ie. weight distribution, fuel load, wind direction, etc. which is why I'm so curious to your results. I spoke with Scott at Mercury racing today about cup and prop rotation and he had little to no insight as to the effects they have on our boats. I guess we are kind of on our own when it comes to propellor results. I'll post results before and after the rework if anybody is interested.
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Old 03-26-2011, 07:24 AM
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I will add this bit of information. When I first met Jim Jones at Awesome, he had spoke of racing a 31 in the Great Lakes Series (don't remember the name). He was working with Hydromotive in Ohio on his prop set-up. That definately was a bravo 1 outdrive and I believe HP500 motors.

I know Randy has spoke of Brett's involvement with his 31 and the results from his handy work.

Simply from experience, appears that there are two prop companies to go to. I do agree that there are some many variables. Weight, weight bias/distribution, and lots more.
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