Low slip rate??

**16ft superboat** · 04-14-2016, 07:04 AM

What's the lowest slip rate you guys have seen?? I'm getting 4%

32p
1.87
7075rpm
110mph

**Mr. Demeanor** · 04-14-2016, 08:07 AM

Slip is so subjective you really cant compare. Ive seen negative slip numbers. There are so manymore variables than just ptch in how a propeller performs.

**16ft superboat** · 04-14-2016, 08:24 AM

I had many many people message me saying my numbers don't add up bc my slip rate is so low. Wouldn't it just mean I got a good setup? If I put a 260 on my boat with same prop and setup and at 7g I'm at 115 I'll be in the negative or 1%. I just don't get it

**transomstand** · 04-14-2016, 08:55 AM

I've gotten to where I pretty disregard slip numbers. Too many variables, props can vary quite a bit in true pitch and tachs can be slightly off. While slip can be valuable as a tool for diagnosing setup, it's only one element and not something I would worry about much. We've seen boats run their best top speeds with double digit slip numbers.

My boat has always run stupid low slip numbers with several different engines, props and tachs. The important number is top speed so I decided years ago that a fast top end number means slip is "good" and a low speed means slip is "bad". It's a much easier system for me to understand

As far as people "proving" over the internet that your boat is fast or slow based on a slip calculation, well...my response to them can't be published here

**Baja170** · 04-14-2016, 09:33 AM

Fastest number on my Cougar at 5600RPM SCREAMING 500EFI IMCO SC outdrive -3 SC lower aired out in light chop with a labbed and worked prop, 485 worth of prop work + shipping back to me, not including new prop and shipping to them, (would prefer to keep it around 5400) was 89.6 calculating to 12% slip. I agree with Transomstand. The calculator can be correct with some setups, with others, it sure looks WAY off.

How did you do yesterday man, you did not update your thread. Glad to see you posting today.

**Onetime** · 04-14-2016, 10:11 AM

I agree to many variables but when comparing on the same boat and power it can be helpful.

A prop guy I have the utmost respect for explained it real well to me once. Basically when everything is set up and running best your riding on the blade tips and the cup not the blade pitch.
Found the lowest slip numbers on chopper style props with the most pronounced cups. Doesn't seem to do it as easily on cleaver blades were the cup is ground in.

**Davidlake** · 04-14-2016, 12:11 PM

I posted this on another site. This is part of what I posted. Some have stated that they have achieved very low slip numbers with their boats, as low as zero slip. So I tried to do some on-line research. Below is an article that explains some of the physics of propellers and why slip is critical for a boat to have thrust. I welcome some conversation regarding this issue, not to cast doubt on anyone, but to try to flush out real world experiences and gain a better understanding. Thanks!

https://www.vicprop.com/propeller101.htm

**Tom Foley** · 04-14-2016, 12:16 PM

Originally Posted by Mr. Demeanor

Slip is so subjective you really cant compare. Ive seen negative slip numbers. There are so manymore variables than just ptch in how a propeller performs.

We all know it can't be negative so the pitch or the RPM is awry .

**Mr. Demeanor** · 04-14-2016, 12:38 PM

Originally Posted by Tom Foley

We all know it can't be negative so the pitch or the RPM is awry .

Or lots of cup making it act bigger. The only time I look at slip is when I am comparing the same prop before and after having work done to it.

**Markus** · 04-15-2016, 11:50 AM

Measuring slip between different propellers is meaningless.

A 32 inch propeller is not 32.0000 inches. It is roughly 32 inches.

**texasvector** · 04-15-2016, 12:24 PM

recently i was running a cut 28 et.......ran 98+ @ 8k....sent prop to shop to reduce the slip and maybe grab a few mph.....well......prop dont slip any more.....lost 500 rpm and few mph.....SMH

**transomstand** · 04-15-2016, 12:28 PM

Originally Posted by texasvector

recently i was running a cut 28 et.......ran 98+ @ 8k...

Hope that wasn't with my housing...that thing better run at least 104

**Jimboat** · 04-15-2016, 12:45 PM

Measuring slip is a good method for comparing 2 setups on same rig. While it can help identify a 'big-picture' issue, it's not particularly helpful as a 'stand-alone' measure of performance or efficiency. Slip is a necessity for a propeller to work. if there is zero slip, then the propeller can't turn at all, generates no force and thus no MPH. So while "less slip" is generally more efficient than "more slip" when measuring 'power efficiency', it does not indicate that a boat will go faster just because of "less slip". "Negative Slip" is a mathematical impossibility. Similarly, a calculation that shows "30% slip" is also likely suspect. More likely, very low or very high calculated slip is more likely to be a faulty RPM reading, faulty MPH measure (GPS are notoriously variant), or an improper representation of the propeller pitch dimension. The rest is just math. [ed: check out my article on "Propeller Slip"]