The shaft power of a ship is 3000 KW, the ship’s speed V is 13.2 knot. Propeller rps is 1.27. Propeller pitch is 5.5m and the speed of advance is 11 Knots. Find: i. Real Slip ii. Wake fraction iii. Propeller thrust, when its efficiency, η = 70%
If you are noticing some error in problems kindly comment below.Thanks
Given
Sp = 3000 KW
V = 13.2 Knots
Rps = 1.27
P = 5.5 m
Va = 11 Knots
To find
1. Real slip, s
2. Wake fraction, w
3. Propeller thrust, T when its efficiency, η = 70%
Solution
RPM , N = Rps x 60
= 1.27 x 60
= 76.2
Theoretical speed Vt = P x N x 60/1852
= 5.5 x 76.2 x 60/1852
= 13.58 Knots
1. Real slip = [(Vt - Va) / Vt] x 100
= [(13.58 - 11) / 13.58] x 100
s = 18.99 %
2. Wake fraction = (V - Va) / V
= (13.2 - 11) / 13.2
w = 0.167
3. It is given that efficiency = 70 %
Therefore Thrust power = Shaft power x Efficiency
= 3000 x 0.7
= 2100 KW
Alternatively Thrust power = Thrust x Speed of advance
= T x Va
2100 = T x 11 x (1852 / 3600 )
Thrust T = 2100 x 3600 / (11 x 1852)
= 371.09 KN
If you are noticing some error in problems kindly comment below.Thanks
Given
Sp = 3000 KW
V = 13.2 Knots
Rps = 1.27
P = 5.5 m
Va = 11 Knots
To find
1. Real slip, s
2. Wake fraction, w
3. Propeller thrust, T when its efficiency, η = 70%
Solution
RPM , N = Rps x 60
= 1.27 x 60
= 76.2
Theoretical speed Vt = P x N x 60/1852
= 5.5 x 76.2 x 60/1852
= 13.58 Knots
1. Real slip = [(Vt - Va) / Vt] x 100
= [(13.58 - 11) / 13.58] x 100
s = 18.99 %
2. Wake fraction = (V - Va) / V
= (13.2 - 11) / 13.2
w = 0.167
3. It is given that efficiency = 70 %
Therefore Thrust power = Shaft power x Efficiency
= 3000 x 0.7
= 2100 KW
Alternatively Thrust power = Thrust x Speed of advance
= T x Va
2100 = T x 11 x (1852 / 3600 )
Thrust T = 2100 x 3600 / (11 x 1852)
= 371.09 KN
By Reeds book, Thrust power= delivered power × propeller efficiency
ReplyDeleteDelivered power = shaft power × transmission efficiency
Shaft power = indicated power × mechanical efficiency
But you mentioned thrust power = shaft power × propeller efficiency.
So kindly solve my doubt. Thanks
Thanks for the message. In question paper they have not mentioned anything about Transmission efficiency. So it assumed as negligible so shaft power will be equal to delivered power. Hope this cleared your doubt.
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