Twin ob cats Whats your prop slip?

[fastcat]

Mine seems to be really high 17 %.

28' cat twin 99 ros 280s.

14.5x32s
1.87 sportmasters
7800 rpms
105 mph gps

Motors are 1.5" above the pads.

[WILDMAN]

Mine is 4% with my 15x30 cleavers. I run 122.5 at 8400 with the props running 5.5" above the bottom and in the tunnels. My labbed 32 cleavers have 5.5% slip at 124.4 mph.

[Hottrucks]

10%
92 mph @ 6700 on my 24 Skater with 220 lazer XRI
spinning 30 mercs ( I think my Mazcos slip less)

[LakeTrash]

I have always wondered how prop manufacturers determine prop pitch. We have one of the major prop builders here. They have the latest digital machines as well as the old pointer system. Placed my unworked Mazco RE4 prop in the machine, started the read at the hub and let it ride up the blade. The pitch varied from 22 at the hub to 29 at the tip and it was stamped a 26.

I asked the owner how they decided which area of the prop to use as the "pitch" number and he said it was an arbitrary guess dependent on the use of the prop.

A lightweight tunnel with a surfacing prop will run further out on the blade actually running at the 28 (my example) spot so that when you calculate slip using the 26 number you get low slip. The heavy boats work the other direction.

Just an observation.

LT

[LubeJobs42]

How do you determine your slip %? I just purchased 3 sets of props from someone. They are all 16.25 Diameter. One is a set of Hering 16.25 x 38P 5 blades. I am on the rev limiter fairly quick. I haven't seen 150 Mph. I was told I should be able to see at least 156 at 6200 RPM. I know other MTI's are using 16.5 ot 16.75 daimeter. How do I determine if my diameter is too small?

[fastcat]

This will help you figure your slip.

http://www.mercuryracing.com/product...s/propcalc.php

[Hottrucks]

people confuse RAKE and Pitch

Rake is the angle at the hub

Pitch is the angle at the center of the blade

example if you mesured the tip you would be messuring CUP

I could go into long winded explination but to lazy to type it when I get back home I will get you a link that can explain in much further detail. I will also post the link ( or you can do a seach) for prop slip calculators...

basicly its rpm, gear ratio, acutual speed , vs theoretical speed this will give you your slip ratio

my boat spins 30 pitch merc labs at 6700 rpm the theoretical speed is 102 mph ( this would be with 0 slip ) how ever my boat only does 92 mph ( real speed) the diffence is 10% = slip ratio

Hope this helps
Jeff

[Liquid Force]

Lubejobs,

What gear ratio are you running?, you will need to input that factor into the calc aswell.

[dreamboater]

28 Skater 300 promax's 1.62 gears with 15x34 @ 6300 - 115.4.........8%. This is the lowest slip I have ever run. I was about 1 7/8" above the bottom and on the edge with water psi and temp. I can not run this setup in the summer due to air and water temp.

[apache21]

The Mercury calculator is right on the number on my Skater. Best speed I have seen is 101 with 2.4 Bp Efi. Mercury Labbed 14.5 x 31 cleavers.

[half fast]

Pitch is not angle ,it is the theoretical distance a prop travels in one revolution. hf...

[LubeJobs42]

Lubejobs,

What gear ratio are you running?, you will need to input that factor into the calc aswell.

Hi, 1:35 ratio. What is an acceptable percentage of slip?

[Liquid Force]

How do you determine your slip %? I just purchased 3 sets of props from someone. They are all 16.25 Diameter. One is a set of Hering 16.25 x 38P 5 blades. I am on the rev limiter fairly quick. I haven't seen 150 Mph. I was told I should be able to see at least 156 at 6200 RPM. I know other MTI's are using 16.5 ot 16.75 daimeter. How do I determine if my diameter is too small?

Lubejobs,

Put those numbers you provided into the calc and if you could achieve 156mph at 6200rpm you would be around 6.5% slip which is pretty damn impressive, you say you can't see 150, and assuming your limiters are at 6200you currently have around 10-11% slip that puts your top speed around 147-148mph. I am far from an expert but would say try a larger diamter prop and see if your slip comes down, you may be running to high an X dimension for that diamater prop (16.25), have you spoken with throttle up or BBlades, they should point you in the right direction, Juile at Throttle Up has built some props for me and have done a good job.

Good Luck and let us know how you get on!!

Cheers

James

[Hottrucks]

Pitch is not angle ,it is the theoretical distance a prop travels in one revolution. hf...

I was using simple word to make it easier???

website I use with my #'s in it:
http://www.go-fast.com/Prop_Slip_Calculator.htm

<BIG><BIG><BIG>Prop Slip Calculator</BIG></BIG></BIG>
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Use this calculator to figure out just about anything in regard to propeller, ratio, RPM and speed. You can change one parameter and recalculate the rest. Use the CalcT button to figure the theoretical speed from the actual speed and slip. Be sure to take a look at the Prop Slip page for an explanation of how to find your prop slip. revised 8-26-24
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<CENTER><!--mstheme-->

<TABLE borderColorDark=#666666 width=793 borderColorLight=#666666 border=2><TBODY><TR><TD vAlign=center align=middle width=89><!--mstheme-->Gear Ratio<!--mstheme--></TD><TD vAlign=center align=middle width=112><!--mstheme-->Pitch<!--mstheme--></TD><TD vAlign=center align=middle width=118><!--mstheme-->RPM<!--mstheme--></TD><TD vAlign=center align=middle width=89 rowSpan=3><!--mstheme--> <!--mstheme--></TD><TD vAlign=center align=middle width=108><!--mstheme-->Theoretical Speed<!--mstheme--></TD><TD vAlign=center align=middle width=216><!--mstheme-->Use this button to calc Theo speed from Slip & Actual Speed<!--mstheme--></TD><TD vAlign=center align=middle width=100><!--mstheme-->Slip<!--mstheme--></TD><TD vAlign=center align=middle width=103><!--mstheme-->Actual Speed<!--mstheme--></TD></TR><TR><TD vAlign=center align=middle width=89><!--mstheme--><INPUT onclick=calc_ratio(this.form) type=button value=Calculate name=Ratio><!--mstheme--></TD><TD vAlign=center align=middle width=112><!--mstheme--><INPUT onclick=calc_pitch(this.form) type=button value=Calculate name=RPM><!--mstheme--></TD><TD vAlign=center align=middle width=118><!--mstheme--><INPUT onclick=calc_rpm(this.form) type=button value=Calculate name=Pitch><!--mstheme--></TD><TD vAlign=center align=middle width=108><!--mstheme--><INPUT onclick=calc_tspeed(this.form) type=button value=Calculate name=TSpeed><!--mstheme--></TD><TD vAlign=center align=middle width=216><!--mstheme--><INPUT onclick=calc_tspeed2(this.form) type=button value="Calc T" name=TSpeed1><!--mstheme--></TD><TD vAlign=center align=middle width=100><!--mstheme--><INPUT onclick=calc_slip(this.form) type=button value=Calculate name=Slip><!--mstheme--></TD><TD vAlign=center align=middle width=103><!--mstheme--><INPUT onclick=calc_speed(this.form) type=button value=Calculate name=Speed><!--mstheme--></TD></TR><TR><TD vAlign=center align=middle width=89><!--mstheme--><!--webbot bot="Validation" s-display-name="ratio" s-data-type="Number" s-number-separators=",." --><INPUT size=4 value=1.87 name=ratio><!--mstheme--></TD><TD vAlign=center align=middle width=112><!--mstheme--><!--webbot bot="Validation" s-display-name="pitch" s-data-type="Integer" s-number-separators="," --><INPUT size=3 value=30 name=pitch><!--mstheme--></TD><TD vAlign=center align=middle width=118><!--mstheme--><!--webbot bot="Validation" s-display-name="rpm" s-data-type="Integer" s-number-separators="," --><INPUT size=6 value=7200 name=rpm><!--mstheme--></TD><TD vAlign=center align=middle width=108><!--mstheme--><!--webbot bot="Validation" s-data-type="Integer" s-number-separators="," --><INPUT size=5 value=109 name=tspeed><!--mstheme--></TD><TD vAlign=center align=middle width=216><!--mstheme--> <!--mstheme--></TD><TD vAlign=center align=middle width=100><!--mstheme--><!--webbot bot="Validation" s-data-type="Integer" s-number-separators="," --><INPUT size=2 value=10 name=slip> %<!--mstheme--></TD><TD vAlign=center align=middle width=103><!--mstheme--><!--webbot bot="Validation" s-display-name="speed" s-data-type="Integer" s-number-separators="," --><INPUT size=5 value=98 name=speed><!--mstheme--></TD></TR></TBODY></TABLE><!--mstheme--></CENTER>

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<SCRIPT language=JavaScript>function calc_tspeed(form){ tspeed = (form.pitch.value*form.rpm.value)/(form.ratio.value*1056) form.tspeed.value = Math.round(tspeed)}function calc_tspeed2(form){ tspeed = form.speed.value/(1-(form.slip.value/100)) form.tspeed.value = Math.round(tspeed)}function calc_slip(form){ slip = 100*(form.tspeed.value-form.speed.value)/(form.tspeed.value) form.slip.value = Math.round(slip)}function calc_pitch(form){ pitch = (form.tspeed.value*form.ratio.value*1056)/form.rpm.value form.pitch.value = Math.round(pitch)}function calc_rpm(form){ rpm =(form.tspeed.value*form.ratio.value*1056)/form.pitch.value form.rpm.value = Math.round(rpm)} function calc_speed(form){ speed = form.tspeed.value*(1-(form.slip.value/100)) form.speed.value = Math.round(speed)}function calc_ratio(form){ ratio = 100*(form.rpm.value*form.pitch.value)/(form.tspeed.value*1056) form.ratio.value = Math.round(ratio)/100 }</SCRIPT> <!--mstheme--><!--msnavigation--><!--msnavigation--><!--msnavigation--><TABLE cellSpacing=0 cellPadding=0 width="100%" border=0><TBODY><TR><TD><!--mstheme--><!--mstheme--><TABLE id=AutoNumber1 style="BORDER-COLLAPSE: collapse" cellSpacing=1 width="100%" border=0><TBODY><TR><TD width="26%"><!--mstheme-->

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