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drive spacers/cleaner water/slip

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Old 06-18-2002, 08:30 PM
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Default drive spacers/cleaner water/slip

As you all already know my set up is a 37 AT, with KE 675 motors.

This is where we are, we are dialing it in right now and getting ready to add spacers in the drives to try and get them a bit deeper in the water, into cleaner water to reduce the slip on the props, and ultimately increase the speed. My best so far was about 97 mph, at 5450 rpms but 14 percent slip with hering 5 blades. Hering told me the average slip factor for his props is somewhere around 9 or 10.

So far we have had high slip numbers, around 14 percent. Now this is the formula as I understand it.

RPMs divided by gear ratio X prop size divided by 1056= 100% efficiency.

Figure the slip from there. High slip, high drives. Low slip, low drives.

So we have some high slip and going to sink the drives a bit with spacers. There is the update so what do you all think?

Last edited by thunderdan; 06-18-2002 at 08:49 PM.
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Old 06-18-2002, 09:29 PM
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Did the spacers help, or not, and are you still on the 1:35 or 1:50 with the herrings.
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Old 06-18-2002, 09:37 PM
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We are still with the 1:5 gears and the herings. We were slightly delayed due to the difficulty procuring the drive spacers.

Tomorrow we will continue our testing Jassman..
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Old 06-18-2002, 10:00 PM
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Dan, help me out! So, theoretically if you get the slip down to 9 to 10% and calculate everything out where do you think you will end up speed wise??
 
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Old 06-18-2002, 11:13 PM
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roughstuff,

Not real sure as to where the speeds will be but theoretically if I lower the slip, then my speed should increase unless I am dragging too much. So from what I understand, if I lower the drives and my slip goes down then I am going in the right direction, if i lower the drives and my slip goes up then I need to raise my x dimesion....I am pretty sure that is correct...

Testing is the only answer.....luckily for me Pat is spending the time to dial it in for me.
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Old 06-19-2002, 07:17 PM
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Thunderdon Have hering rework props to lower slip .

If you lower drives they will slow you down.

Revers props that may help.

RPM xPITCh DIVID GEAR RATIO = 100%

figre the slip from there.



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Old 06-19-2002, 07:22 PM
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rpm X pitch DIVID by GEAR RATIO DIVID 1056 =100%

FIGURE the slip from there .
 
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Old 06-19-2002, 07:27 PM
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sam,

but what if i add the spacers-lowering my drives -that could possibly lower my slip, increasing my speed, no?

In the reverse if I lower the drives and my slip increases than I need to raise my drives, No?
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Old 06-19-2002, 07:54 PM
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Remember the 92-95mph "wall" I mentioned in the previous
thread ? You've found it. How many pins of trim can you run
before it starts to blow out when your running with the highest
X ?

JD
 
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Old 06-19-2002, 07:57 PM
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"Not real sure as to where the speeds will be but theoretically if I lower the slip, then my speed should increase unless I am dragging too much."

I'm sure you are doing fine, but this statement gives me the impresion there may be some confusion. If you are using the same prop, if you lower the slip, by definition you are going faster. No "unless." The problem with "reduced" formulae is it is easy to forget the factors.

Engine RPM / drive gear ratio = prop RPM

Theoretical speed = prop RPM x (pitch/12) x 60 / 5280

pitch in inches, 60 minutes per hour, 5280 feet per mile

so ts = 102.27 if you use a 30" pitch prop.

Prop eff = (102.27 - GPS speed) / 102.27 (times 100 if you like)

Asyour speed (GPS speed) is one of the factors, you can't lower slip without going faster.

Make changes that give you less slip...it will not be limited to just up - down.

Ted
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