You must average 16.25 knots to reach port at a designated time. Your propeller has a pitch of 21' 08", and you estimate 4% negative slip. How many RPM's must you average to arrive on time?
Given:
S.O.A = 16.25 kts
Pitch = 21' 08" (8inch x 1 foot = 8 ft = 0.66 ft)
= 21.66 ft 12inch 12
Slip = - 4%
What is asked?
Average revolution per minute (RPM)
Solution:
1. We have to get first the value of efficiency.
efficiency = 100 - (-4)
100
= 100 + 4
100
= 104
100
Eff = 1.04
2. To solve for RPM, we have to use the formula for S.O.A. and then cross multiply to derive the formula for the revolution per minute.
S.O.A = RPM x P x 60 x Eff
6080 (We have to cross multiply)
RPM x P x 60 x Eff = S.O.A x 6080
RPM x P x 60 x Eff = S.O.A x 6080
P x 60 x Eff P x 60 x Eff
RPM xP x 60 x Eff = S.O.A x 6080
P x 60 x Eff P x 60 x Eff (Do some cancellation)
RPM = S.O.A x 6080
P x 60 x Eff
= 16.25 x 6080
21.66 x 60 x 1.04
= 98800
1351.58
RPM = 73
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Given:
S.O.A = 16.25 kts
Pitch = 21' 08" (8
= 21.66 ft 12
Slip = - 4%
What is asked?
Average revolution per minute (RPM)
Solution:
1. We have to get first the value of efficiency.
efficiency = 100 - (-4)
100
= 100 + 4
100
= 104
100
Eff = 1.04
2. To solve for RPM, we have to use the formula for S.O.A. and then cross multiply to derive the formula for the revolution per minute.
S.O.A = RPM x P x 60 x Eff
6080 (We have to cross multiply)
RPM x P x 60 x Eff = S.O.A x 6080
RPM x P x 60 x Eff = S.O.A x 6080
P x 60 x Eff P x 60 x Eff
RPM x
RPM = S.O.A x 6080
P x 60 x Eff
= 16.25 x 6080
21.66 x 60 x 1.04
= 98800
1351.58
RPM = 73
If you find this blog helpful, please click the share button below to share this post to your friends. Sharing is caring...
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