Unrealistic low prop slip
 

Friend of mine has a 29 ft rib with twin 250 verado's

Spinning (brand new) 23 P Rev 4 props @ 6010 rpm and seeing 70 mph on 2 different GPS :D

After prop slip calculation theoretical topspeed = 71 mph meaning this rig only has 1 % propslip which is unrealistic :mad:

Merc's website stated for Verado 250 only 1 gear ratio 1.85

Where is the error or are these props so perfect ??? :rolleyes: :rolleyes:

GPS's can be off, Tach's are always slightly off.

Example........
True speed...69 mph
True rpm........6250
True slip.........6.22%

Ribs can be real efficiant.

Check that the GPS is not in KPH.

That will only make things worse... 70kph~80mph

No, I was thinking in kilometers but after thinking about it that would yield unrealistic high slippage numbers. My GPS can be set to Knots kts , MPH, or Kilometers per hour kph.

Yes, speed was GPS measured (by two different GPS 1 handheld / 1 fixe in the boat) in kph but converted to mph when putting info on this board.

Changed props last week => almost same story

Rev4 21P turning at rev limiter @ 6400 rpm GPS speed is 106 kph = 66,25 mph
Calculating slip = < 4%

Mirage 3 BL 23P hitting rev limiter 6400 RPM
Top speed was 113 kph = 71 mph = < 5% prop slip

Again very unrealistic low prop slip numbers IMO

Now lets try some Bravo 1 4 blades (or even better Lab finished ones) :D :D

Prop is really higher pitch, if it behaves as a 22" then you are up to 9% slip from 4%, still low but better. Gear ratio could be different of course.

With these numbers, Labs will make you fly!

Ah, sorry - my mistake :rolleyes: