Prop calculator ( slip % number )

[Christopher Willis]

Using the prop calculator , what's the best all round slip % number to use ? I know each prop is different . Just wondering what average ball park would be !!! ( USING THE ONE ON BYUBOYZ )

Thanks Again

[pyro]

Prop pitch is subjective, because it's only a physical measurement.

There is no "normal" or "baseline" slip percentage.

[rev.ronnie]

I usually throw in 5-7% for sake of argument. I have a couple of props that actually calculate out at less than zero slip though, when rpm is read against GPS readings, so that's where Chad's point comes into play.

[Christopher Willis]

Thanks , just looking for a ball park % number to plug in . I was using 4%

[FrenchPhil]

Cats around 5, vee's 10

[pyro]

By the numbers, mine is around 12-15%, but that's not what matters. The quickest or fastest prop doesn't always have a low slip number in paper.

[Fish]

i usually start with 10% as a WAG and then adjust from there.

[RIVERRUMMER 70]

by the numbers, mine is around 12-15%, but that's not what matters. The quickest or fastest prop "you have tried so far" doesn't always have a low slip number on paper.

i believe the "best" prop IS the one that pushes your boat the fastest AND has a low slip #. You just havent found it yet!
YOU FOUND A PROP THAT WILL PUSH YOU TO A SPEED YOU FEEL IS "GOOD ENOUGH" @ 12-15% ON PAPER.
DO YOU BELIEVE A PROP THAT WILL PERFORM BETTER EXISTS? OR COULD BE BUILT?
I DO! WILL THAT PROP HAVE A LOWER SLIP # I THINK SO!
SO IS IT A COMPROMISE TO ACCEPT A SLIP # OF 12-15% AS YOUR BOAT IS FAST ENOUGH FOR YOU?
OR DID.... TIME , MONEY, PATIENCE, PLAY A ROLE IN YOUR PROP CHOICE?
YES......? JUST SAYIN. YOUR COMMENT MAY APPLY TO YOUR SITUATION BUT CERTAINLY NOT EVERYONE.:cheers:

[wired247]

I dont think slip numbers matter all that much. Say I run a 28 pitch prop that slips 15% at 7000 RPM and I go 84 MPH. Then I try a 25 pitch prop that slips 5% and goes 84 MPH at 7000 RPM but is a dog out of the hole because it doesnt spool up fast enough I havent really gained anything by slipping less. Ive used props that on paper were negative slip props because their maker produced bogus pitch numbers. Unless you compare apples to apples and oranges to oranges and measure pitch yourself you cant trust slip numbers much when comparing props.

[pyro]

Pitch numbers aren't necessarily "bogus", but they're based on physical measurements of the prop blades, and the resulting "pitch" measurement may not reflect how the prop runs in the real world.

Slip should only be used as a baseline constant in calculations when you want to try out another prop of the same model in a different pitch, so you can get an idea of what RPM or speed the new prop would run.

[cptunnel]

so it is possible to run 1-2% ? cause what im seeing thats what its calculating..

[native2]

I usually seem to run in the 10-15 percent range according to the numbers... The guys that run the 5% numbers probably have lots of prop work done. Most times prop work includes tip cup, if cup is added you have increased the pitch potentially lower your slip numbers... After I add cup to a prop i usually add one inch in picth when running the numbers. Pitch is calculated on average across the blade. a 28 picth prop may have a leading edge pitch of 25 inches and have a trailing edge pitch of 30+... It all depends on prop ad whats been done to it. JMO.

[cptunnel]

gotcha. well guess my mazco is done up a lil more than i thought :cheers:

[Motv18]

so it is possible to run 1-2% ? cause what im seeing thats what its calculating..

Yep you can turn 86 on a theory of 85. More or less showing effective thrust cup opposed to grip cornering cup. Also could indicate severe tach error.

[LaveyT]

efficiency and prop slip are two different things.

[dwilfong]

A prop will not go any faster than the lead in pitch. the first 20deg of a prop will tell you how fast it will go max. RPM X LE pitch /1057 will give you max speed with no slip.
All props have progression built in to them how much will determine the bite of the prop.
More cup will help with slip but will load the eng. it is a balancing game as to how much power you have.
LE pitch is less then average pitch .
A 28 pitch prop is not 28 on the lead in and not all 28 have the same lead in.
LE pitch is what you need to know to compare one prop to the next not average pitch.

[brockshydro]

I was seeing 3% with my yamaha with Titus coned lower went to a merc motor with a bobs coned merc lower same prop same ratio slip numbers went to 10%

[Jimboat]

By the numbers, mine is around 12-15%, but that's not what matters. The quickest or fastest prop doesn't always have a low slip number in paper.
Yup! Pryo is right.

Propeller slip is useful for comparing different setups. The % number itself doesn't really mean alot, except to compare to other results. For example, a lower % slip might seem to be more 'efficient' and thus 'better'...but not necessarily true. It's kind of a confusing theory. Slip is a requirement for a propeller to work - less slip means more energy conversion, but if slip were, for example, zero, then the propeller could not turn at all! So LESS % slip is not necessarily BETTER.

There is no 'rule of thumb' for 'best slip %', and it's not all related to just the propeller (eg: engine trim, height, etc.)

All that said, most performance hulls/prop setups are usually in the 10% range. When you're measuring more or less than this range, it gives good indications of what you might be able to do with prop or setup changes to improve performance of your setup.

[dwilfong]

293276Here is some good reading. helps explain what is what with prop pitch. I is in refernce to R/C boat props but a prop is a prop and 100MPH is 100MPH in any size boat.

[Motv18]

I don't think many take it this far, but if you have an ajustabale set up you can benifit from lowering and resetting height. I have also seen people go for full trim ( as for out/up as it goes every time) missing a props sweet spot.

A good example is my boat. My black max at my current setup with the sender set to 20 if I pined it in the last hole out. Will hold to about 14 then vent fully no gradual bite loss. My spitfire holds to 16 and will lose bite slowly to 19. My solas holds to 20 and beyond rostering and loosening some bite slowly. The slip beyond the grip but still not over max rpm is excessive, but also beyond the performance envolope of my set up. If I measure it at the max edge of bite I get around 7-12 or 20% on the black max. Motors Just to to high for it.

If you watch your gps and tach you should find a spot in the trim were you gain leg out and rpm but drop speed you hold hear if it doesn't pick the speed back up your over trimmed on that prop bump the trim back down. That's were she runs at that x dimension. I also calibrate something like comand compas app so I can use my phone to measure bow degrees and if I list at speed.

Im anal though and and will plot total performance graphs measur Gph readings. Run full half and empty max load me only. A lot of useless to most people stuff.