Only 5% slip with SS prop? Is that possible?

[StangLX302]

I plug in my numbers here http://www.go-fast.com/Prop_Slip_Calculator.htm and it says I'm only getting 5% prop slip. Is that possible on a light boat with an SS prop? In case you want to double check, My numbers are 2.0 Gear ratio, 21 pitch, 4800 RPM, 45.6 GPS verified MPH.

 

[Dhadley]

Re: Only 5% slip with SS prop? Is that possible?

We see %'s like that, usually on a performance boat. If you're sure the GPS is accurate then verify the tach and gear ratio. Once that's verified, then you're all set. Don't change a thing!

 

[Silvertip]

Re: Only 5% slip with SS prop? Is that possible?

If the prop is cupped, many prop calculators have you add one inch of pitch to the actual pitch of the prop. If you didn't do that, the numbers would be slightly different.

 

[MikDee]

Re: Only 5% slip with SS prop? Is that possible?

I plug in my numbers here http://www.go-fast.com/Prop_Slip_Calculator.htm and it says I'm only getting 5% prop slip. Is that possible on a light boat with an SS prop? In case you want to double check, My numbers are 2.0 Gear ratio, 21 pitch, 4800 RPM, 45.6 GPS verified MPH.

This is a formula I read about yrs ago in an outboard owners handbook, and I've been using this for years to do in my head! Apparently the prop calculator is based on this:

First take the prop pitch -1 = 20

Then RPM divided by the gear ratio = 4800rpm divided by 2.0 = 2400rpm X 20 or (prop pitch -1) = 48.000, or 48mph divided by 5% slip = 45.6 mph

 

[Tail_Gunner]

Re: Only 5% slip with SS prop? Is that possible?

We see %'s like that, usually on a performance boat. If you're sure the GPS is accurate then verify the tach and gear ratio. Once that's verified, then you're all set. Don't change a thing!

I'd take a hint here.......

 

[QC]

Re: Only 5% slip with SS prop? Is that possible?

I'd take a hint here.......

Me too . . .

 

[StangLX302]

Re: Only 5% slip with SS prop? Is that possible?

I'd take a hint here.......

Meaning, I should have my tach checked or I picked out a really good prop?

 

[Dhadley]

Re: Only 5% slip with SS prop? Is that possible?

If the tach and gear ratio are accurate, you nailed it! It's not often we see that much efficiency -- congrats!

 

[Texasmark]

Re: Only 5% slip with SS prop? Is that possible?

Yeah but I made that mistake too, the first time I calculated my slip using the "BAM" calculator on www, I forgot to take into account the cupping addition and once I added it to the pitch, the slip was much more in line with what you guys would expect.

Mark

 

[Tail_Gunner]

Re: Only 5% slip with SS prop? Is that possible?

Yeah but I made that mistake too, the first time I calculated my slip using the "BAM" calculator on www, I forgot to take into account the cupping addition and once I added it to the pitch, the slip was much more in line with what you guys would expect.

Mark

Same here ran a 4bl Stilletto and it yeilded about a 4% slip factor, WH pointed out the cupping made it effectivly a 21p yeilding about a 8-9% slip, cant ask for more..

 

[StangLX302]

Re: Only 5% slip with SS prop? Is that possible?

I just entered 22 pitch instead of 21 pitch and got 9%. That's still pretty good, right?

 

[Dhadley]

Re: Only 5% slip with SS prop? Is that possible?

That's still very good.

Food for thought -- is your GPS reading killometers or mph? I'm sure it's mph but I noticed mine was reading km when I got the boat.

 

[StangLX302]

Re: Only 5% slip with SS prop? Is that possible?

MPH....I'm positive.

 

[rondi]

Re: Only 5% slip with SS prop? Is that possible?

Very Good Stang!

This was done simply by replacing the stock Black Max with the SS Vengeance prop at the same pitch? . . . . BTW, is the Vengeance cupped? I didn't think it was.

WH stated that the Vengeance was a very basic "entry level" prop . . . great that you were able to get those results from it.

 

[StangLX302]

Re: Only 5% slip with SS prop? Is that possible?

Very Good Stang!

This was done simply by replacing the stock Black Max with the SS Vengeance prop at the same pitch? . . . . BTW, is the Vengeance cupped? I didn't think it was.

WH stated that the Vengeance was a very basic "entry level" prop . . . great that you were able to get those results from it.

Yeap. It's a 13.75" x 21 pitch Vengeance. I'm very happy with it. I didn't think it was cupped either. Check on the BOC. I did a little review on it. I'm taking everyone tubing this weekend, so I'm really going to put it to the test.

 

[walleyehed]

Re: Only 5% slip with SS prop? Is that possible?

Yes, I did say it is an entry level SS prop, and yes, it is cupped, but not to the extent you would find on say...a Turbo TXP, or even a Turbo1 for that matter.
Cupping is a very loosely used term..where it is, is as important as how much it's cupped.
If the numbers you list are correct, I'm impressed and I'm sure Merc would be too....that high of efficiency is not common for a Vengeance...once again...I'm impressed!
If possible, could you verify the final drive ratio? Or, give the year and model of engine/out-drive....I'm not getting the same numbers as the rest of ya..

 

[StangLX302]

Re: Only 5% slip with SS prop? Is that possible?

Yes, I did say it is an entry level SS prop, and yes, it is cupped, but not to the extent you would find on say...a Turbo TXP, or even a Turbo1 for that matter.
Cupping is a very loosely used term..where it is, is as important as how much it's cupped.
If the numbers you list are correct, I'm impressed and I'm sure Merc would be too....that high of efficiency is not common for a Vengeance...once again...I'm impressed!
If possible, could you verify the final drive ratio? Or, give the year and model of engine/out-drive....I'm not getting the same numbers as the rest of ya..

It's a 2006 Bayliner 175 with a 3.0 Merc and an Alpha 1 Gen II Drive with a 2.0 ratio. There is a sticker on the drive that verifies the ratio.

 

[walleyehed]

Re: Only 5% slip with SS prop? Is that possible?

You're correct...with those numbers, I came up with 8.8% slip....still quite impressive to me for that prop.
I have the Vengeance in 6 different pitches that I ran in several of the prop tests that I've done and the best I could acheive with any of them was 10.7% on a wellcraft with a 305. This boat ran an Enertia at 8.7% slip, and a Turbo1 at 9.1%.
I guess as long as you're happy, that's all that matters but I feel the tach is "slightly" off....
I know, I know...I'm too critical about the numbers...

 

[Texasmark]

Re: Only 5% slip with SS prop? Is that possible?

Hey Kenny, since you mentioned the Enertia, when are we going to get your test data and comments on that prop you promised us?....................or have you published that and I missed it.

Mark

 

[walleyehed]

Re: Only 5% slip with SS prop? Is that possible?

When I finished the testing, the numbers between the 18 and 19 were not coming out where they wanted...from me AND others...
They ask for the 18 and 19 back and said I would receive "new" production props...well, they never came....
When I've called and talked with them, they say they made the changes they needed and are getting the numbers expected, so I'm guessing they don't need me for anymore testing..??
The only obvious item I can tell you (beings the 18-19 numbers were biased by design) is that all the Enertias I ran would pull about 100RPM more than any prop in the same class, some about 150 more. Most were all slightly faster as well...some maybe only .5mph, but the 21 was slower than 1 prop in that run and likely not the same prop in this class, yet still showed better numbers and that was (of course) a Turbo TXP.