Originally Posted by Actionboat.dk
Achieve 68.2kn with 25* revelution props
both rig up for charter.
Could you please help me out here, because there is something I do not understand.
That speed is normally not possible with that pitch on the propell. If you should get that speed 68.2 knots), you would need a slip-percentage of 5.8% at 6500rpm!!!
Normal slippercentage is 12-15% for a 29 feet rib with twin engines fitted for chartering 12 people.
25" (pitch)x2.54 (inch) =63.5cm pr rev.
Rev pr hour is 6500 (min) x 60 (minutes) 390.000
63.5x390.000= 24.765.000 (are number of cm pr hour.)
The gearratio is 1.85
24.765.000:1.85= 13.386.486 cm pr hour
13.386.486cm pr hour is 134 km/t
134:1.85 (knots) = 72.4 knots pr hour.
This is if there is no slip.
A slippercentage of 12, which is the best you nomally can get, will give you a speed of 72.4x.88=63.7 knots.
You claim to have a slip of only 4.2 knots that is (4.2:72.4)=5.8% slip!
We both know that normally it is not possible.
How do you get that speed? Are your engines doing more than 6500 rpm, are you going with the current, wich has a speed of 4.5 knots or is there any other solution to this that I do not understand?
Sorry to ask, but interested in learning.