V-drive formula to calc prop slip

[Knotty Girl]

I liked the spread sheet that was posted a while back. So that you don't have to guess what your prop slip is you can use this formula. SLIP= Speed(MPH) x1056 x Drive Ratio
          -------------------------------------- x 100
                        RPM x Pitch (in.)

There is an app for that. If you have a smart phone look for Hering Propellers.

Whacker boats do not have any slip do they Captin  :shocked:

 

[Captin Hazlewood]

Propeller slip is really just a guesstimate. It is really only useful to compare setup changes with the same propeller. Your propeller is stamped with Diameter and Pitch eg: 14x32. This propeller in theory should travel 32 inches for each revolution it turns. But getting the pitch perfect is not an exact science, the pitch just like bass boat speedometers can be either optimistic or pessimistic. Since we are turning this propeller in a fluid it is going to slip. Since the measurement of pitch is not perfect, this is why I say it is only useful to compare setup changes with the same propeller. That said I'm running about 14-16% using a 4blade 14x32 thru 1.62 gears at 6200-6300 rpm... you do the math...

 

[HellinnFrnt]

OK OK 31.6%  Was this the max rpm for the boat?? j.j.

No 55@4800 was all it would do without clatter ...  it'll spin over 7200 but not with the fuel I'm using .... I think ... it spun faster with no knock with the mag in it. now it starts clattering right at 5k with 93 octane and booster. I know it's got a high lift cam (over .600) may pull it this week and see what all is in it. Man I hate pulling motor's that still run ...

 

[73 Sanger Flat]

go buy 5 gallon of 112-or 114 fuel and then try it , sound like yo have too much compression or you put to much timimg in it .. Keep timing about 34-36* and go back out and try it ..

 

[Carnivalride]

Propeller slip is really just a guesstimate. It is really only useful to compare setup changes with the same propeller. Your propeller is stamped with Diameter and Pitch eg: 14x32. This propeller in theory should travel 32 inches for each revolution it turns. But getting the pitch perfect is not an exact science, the pitch just like bass boat speedometers can be either optimistic or pessimistic. Since we are turning this propeller in a fluid it is going to slip. Since the measurement of pitch is not perfect, this is why I say it is only useful to compare setup changes with the same propeller. That said I'm running about 14-16% using a 4blade 14x32 thru 1.62 gears at 6200-6300 rpm... you do the math...

The problem is your 1.62 is not an overdrive ratio it's an underdrive so

it should be (6200/1.62)/(1056/32)=115.97 x .86 = 99.7mph

so with the info you gave I show you running 97.4-101.3mph

 

[Knotty Girl]

Man you guys are splitting hairs, Put it in the water hammer down then look at GPS  think.gif  :smile16:  jump.gif Just messing with ya'll

 

[HellinnFrnt]

Man you guys are splitting hairs, Put it in the water hammer down then look at GPS  think.gif  :smile16:  jump.gif Just messing with ya'll

thats cause we actually have blades .....

 

[ChryslerJet]

Man you guys are splitting hairs, Put it in the water hammer down then look at GPS  think.gif :smile16: jump.gif Just messing with ya'll

thats cause we actually have blades .....

Jets have blades we just don't like to show them off.  We are more protective of our blades.

 

[spd500]

Jets have blades we just don't like to show them off.  We are more protective of our blades.

Mine dont  think.gif Have you seen the inside of a real jet drive  :smile21: We use an impeller  :smile17:

 

[Captin Hazlewood]

Propeller slip is really just a guesstimate. It is really only useful to compare setup changes with the same propeller. Your propeller is stamped with Diameter and Pitch eg: 14x32. This propeller in theory should travel 32 inches for each revolution it turns. But getting the pitch perfect is not an exact science, the pitch just like bass boat speedometers can be either optimistic or pessimistic. Since we are turning this propeller in a fluid it is going to slip. Since the measurement of pitch is not perfect, this is why I say it is only useful to compare setup changes with the same propeller. That said I'm running about 14-16% using a 4blade 14x32 thru 1.62 gears at 6200-6300 rpm... you do the math...

The problem is your 1.62 is not an overdrive ratio it's an underdrive so

it should be (6200/1.62)/(1056/32)=115.97 x .86 = 99.7mph

so with the info you gave I show you running 97.4-101.3mph

I don't think my motor would work so well with an overdrive, but your math is correct.