Can you briefly describe, how you calculated thrust force?
There are several ways that I've found how to do it… and I am not happy with any of them
- I'm searching since weeks for this stuff but haven't found anything better so far.
The most primitive is just a rule of thumb used by normal boat users: For a good propeller the rule of thumb is:
HP * 20 = Thrust in LBS
would be:
1400 * 20 = 28000 lbs
well… I guess it's clear that this is nonsense
Next thing is the "pullard boll" (boat/propeller is fixed in the water and does not move)thrust = 11.87 * (SHP * DiameterOfThePropellerInInches)^0.67 (power of 0.67)
would be:
11.87 * (1400 * 63.779527559124)^0.67 = 24631 lbs
Next estimation is (SI units):(BrakePower * 0.5) / BoatSpeed*0.95 (0.5 is estimation of Propulsive Efficiency which is a bit low as it can be usually 0.5-0.7)
would be:
(1400*745.6998 * 0.5) / (17.7 * 0.51444) = 57326 N or 12887 lbs
This is also nonsense because it uses the speed of the boat which is not correct, the correct calculation would use the speed of advance of the propeller
What I currently use is:LBP (Lenght between perpendiculars at the water line) = 62.27 meters
B (Beam - I ignore the saddle tanks) = 4.7 meters
T (draugth) = 4.74 meters
Displacement = 769
Density (of Water) = 1025
StandardTon = 1016
RPM = 470
HP = 1400
VS = 17.7 kn (speed of the boat)
Volume = Displacement * (StandardTon/1000)*(1000/Density)
Blockcoefficient = Volume / (LBP*B*T)
PropulsiveEfficiency = 0.836 - (0.000165 * RPM * Volume^1/6) (An estimation by Henschke, 1965)
WaveFraction = (BlockCoefficient / 2) - 0.05 (Taylor)
VA = VS - (VS * WaveFraction) (speed of advance of the propeller)
Watt = HP*745.69987158227
VA = VA * 0.5144444 (convert to meter per second)
Thrust Force = (Watt*PropulsiveEfficiency) / VA = 88970.76 N
= 20001.42 lbsusually you would also add the Coefficient of hull efficiency (close to 1) to the calculation…
HullEfficiency = 0.98
Thrust Force = (Watt*PropulsiveEfficiency) / HullEfficiency*VA = 90786.48 N = 20409.61 lbs