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Question regarding Pitch vs Slip

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Old 04-14-2005, 09:19 PM
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Default Question regarding Pitch vs Slip

I have a Baja 36 Outlaw, twin 500 EFI's.

Was running 26 Pitch Bravo One 4-blades labbed by Throttle up.

Just rebuilt the engines and they ended up on the dyno about 50 to 60 HP better than stock with the accessories on.

Using the prop slip calulators I was getting 15% slip before the rebuild.

I'm very sure I can turn at least 28"s now.

My question is regarding slip. When you go up a pitch does it remain the same as before, or does slip increase?

Trying to calulate possible top speed.

Thanks in advance.

Doc
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Old 04-15-2005, 08:23 AM
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Default Re: Question regarding Pitch vs Slip

Use horsepower to calculate speed increase. In your case you should see about a 4-5 mph increase in your top end. This is equal to about 1 1/2" of pitch or 350 rpm. If you were turning 5000 rpm at WOT before the motors were worked you will be at the rev limiter of you motor. If you were already at the rev limiter then increasing the pitch an inch should help but may not be quite enough.

As far as slip staying the same with a power increase sometimes it does and sometimes not. There are so many factors involved with the power increase that your slip could increase or decrease with the additional power. An increase in pitch increases the stern lift of the prop which typically increases the slip, but not always.

Remember to use 25 as the pitch number when calculating your slip with your props. It will yield a more accurate slip number as that is closer to the true pitch of the your props.

Matt
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Old 04-15-2005, 09:22 AM
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Default Re: Question regarding Pitch vs Slip

Thanks Matt, very much appreciated.

I'll be back in touch with you.
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Old 04-15-2005, 12:45 PM
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Smile Re: Question regarding Pitch vs Slip

My experience has been as you increase pitch the slip goes down with the same power. As you increase power and speed goes up, boat attitude will change and slip may change too. Use your current slip factor though to figure your possible speed increas with new power and pitch.

Brett Anderson / BBLADES Professional Propellers
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Old 04-18-2005, 07:00 AM
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Default Re: Question regarding Pitch vs Slip

Quote:
Originally Posted by throttleup
Use horsepower to calculate speed increase. In your case you should see about a 4-5 mph increase in your top end. This is equal to about 1 1/2" of pitch or 350 rpm. If you were turning 5000 rpm at WOT before the motors were worked you will be at the rev limiter of you motor. If you were already at the rev limiter then increasing the pitch an inch should help but may not be quite enough.

As far as slip staying the same with a power increase sometimes it does and sometimes not. There are so many factors involved with the power increase that your slip could increase or decrease with the additional power. An increase in pitch increases the stern lift of the prop which typically increases the slip, but not always.

Remember to use 25 as the pitch number when calculating your slip with your props. It will yield a more accurate slip number as that is closer to the true pitch of the your props.

Matt
With Bravo 1 four blades you cut off 1 pitch to get the correct slip factor? It it the same for Merc labbed Bravo 1's?
Thanks
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Old 04-18-2005, 11:13 AM
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Smile Re: Question regarding Pitch vs Slip

Yes, it still the same. When Mercury Labs a propeller to a standard specification, no actual pitch changing is done.

Brett Anderson
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