What is normal prop slip?

[txtaz]

After Woodsy posted the link to the prop calculator, I started playing with it. Pretty cool thing. I get a slip of 13% on a 18 classic w/25p Mirage plus. Is this a good number?
Thanks,
Wes

[ChromeGorilla]

I know when I use the calculator I get just under 8% 7.69 or something like that, can't remember.

[Cuda]

13 ain't bad, 10 and under is very good.

[Lenny]

I have heard the same. 7%-10%.

I am at 19% :eek: but that is changing soon :)

13% is a tad on the higher side I think from "achievable optimum."

[RedDog]

After Woodsy posted the link to the prop calculator, I started playing with it. Pretty cool thing. I get a slip of 13% on a 18 classic w/25p Mirage plus. Is this a good number?
Thanks,
Wes

Is that on a 1.5:1 Bravo drive? If so, sounds like you are running too much pitch unless you have a lot of HP. What RPMs are you spinning with the 25" Mirage?

[txtaz]

Yeah Red it's a 1.5:1 Bravo. I'm only spinning 4600 RPM's 2 people full gas at 63.1 GPS. I'm pretty sure it's a stock 350 sbc Mag about 300hp. I'm also pretty sure it's the same prop that Ted put on it.
I'm going to try a 23P sometime soon I hope, let you know how it runs.
Wes

[EricG]

I have heard the same. 7%-10%.

I am at 19% :eek: but that is changing soon :)

13% is a tad on the higher side I think from "achievable optimum."

Right there with you Lenny, 17-18%. Have you gotten any results on the Solas yet? Even if it isn't an optimal run, I'd love to hear a hint of how it's working...

EG

[Lenny]

Eric, I haven't run the Solas yet. I wanted the boat running first. I am seeing 5200-5300 with the 24" Ultra on there as of NOW. That is two people, totally full tank. So, figure about an extra 550 pounds of fuel and people, not to mention the 50 pound tool box I take with me 'cuz I am a pessimist ;)

So running light, low fuel, me alone I will probably see 5400 rpms which is a tad high to be sure for a stock-ish motor and no HD components. ( oh-well :D )

I am going to run the Solas and the Ultra and a COMPLETE, list of numbers and revs. The tach was checked against the scope and it is all but bang-on all the way up to 3500 within 0-50 rpms. That was checked too. I am waiting for some spare time and a NICE warm day as I will have to stand in the water to make prop changes and change rotation. I will refill the tank between props to be perfectly fair. 2500-3000-3500-4000-4500-5000 and WOT in both holes, and both props. Seeing the SOLAS is a 21 but is 15 5/8" :eek: and has a huge blade area, it will be interesting. The SOLAS is equal to the bottom of the skeg on the drive in height. You really don't want to be hitting the bottom of the drive on anything to be sure.

I will keep you posted. Griz said I should see numbers around 7-10% so as you can see the drop from 24" P to 21" P should be made up for with the better slip numbers. It will also be nice to get rid of this "centrifigal clutch I have created" eith the Ultra in the 3rd hole ;) The slingshot effect is neat tho.

[Cuda]

I was very surprised today when I ran the numbers for the first time on the Minx. I'm spinning a 21 cleaver and getting a 7% prop slip. I was amazed because I've heard so much about cleavers being old technology, that I was expecting somewhere around 20%.

[Lenny]

Wide open Joe ? or at what revs. ? I am using WOT for slip calc's.

[gcarter]

Yeah Red it's a 1.5:1 Bravo. I'm only spinning 4600 RPM's 2 people full gas at 63.1 GPS. I'm pretty sure it's a stock 350 sbc Mag about 300hp. I'm also pretty sure it's the same prop that Ted put on it.
I'm going to try a 23P sometime soon I hope, let you know how it runs.
Wes
Hey Wes, I was running a labbed 25" cleaver on the Minx, 1.5/1 Alpha, two people, 3/4 fuel, 4550 RPM, and 64 MPH. Of course the Minx weighs several hundred pounds more than the 18.
Now I'm looking in the 23"- 24" range. Bid on a few Turbos on eBay, nothing yet. :smash:

[Cuda]

Wide open Joe ? or at what revs. ? I am using WOT for slip calc's.
No, not wot. I checked it at 3100 rpm, and at 4200, both times came up with 7%. Will it drop at wot?

[RedDog]

No, not wot. I checked it at 3100 rpm, and at 4200, both times came up with 7%. Will it drop at wot?
I don't know about a cleaver, but my slip goes down the faster I go (Mirage Plus or Turbo I)

[Cuda]

I have a 24 Turbo I'm going to try out too. The cleaver felt a little dicey above 50 mph, it may just be the nature of the beast (the Minx), but I'm thinking a round ear may handle better at speed. Next hooky day, I'll find out. :)

[txtaz]

Thanks for the info guys. What is labbing and how does it affect slip?
Wes

[gcarter]

Thanks for the info guys. What is labbing and how does it affect slip?
Wes
Labbing thins the blades (a lot) and trues them. Mainly reduces parasite drag so you can get an additional 100 to 300 RPM, hence higher spped.
I read on one of the prop sites labbing significantly reduces strength. Emphasis on significant!!!!!

[txtaz]

I read on one of the prop sites labbing significantly reduces strength. Emphasis on significant!!!!!
:shocking: :shocking: :shocking:
Sounds like I need another way to get the revs with the things I've hit in the past.
Thanks George,
Wes

[Cuda]

Labbing thins the blades (a lot) and trues them. Mainly reduces parasite drag so you can get an additional 100 to 300 RPM, hence higher spped.
I read on one of the prop sites labbing significantly reduces strength. Emphasis on significant!!!!!
Yes, the thinning of the steel makes them more prone to damage.

[blackhawk]

Cuda, you need to figure out slip at WFO and trimmed for max speed. Mid range slip numbers don't mean much because there are a lot of ways to get a certain rpm(trim vs throttle).

txtaz, labbing does thin the blades but if done right it does not reduce strength too much. But you should try not to hit things! ;) I just bought a 25 Mirage Plus and I am going to send it out to get labbed. 13% is not bad, lower would be better but it's not bad. In fact, Turbo told me their Turbo 1 prop is designed for 12% slip. I'm shooting for 10%.

Another note for prop slip. CHECK YOUR TACH! Every boat I have owned had a tach that was off.